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12.1: N and S assimilation from inorganic form - Biology

12.1: N and S assimilation from inorganic form - Biology


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NITROGEN REDUCTION AND ASSIMILATION

Ammonia Synthesis in Plants, fungi, and some microorganisms:

Nitrate Reductase

[mathrm{NO_{3}^{-}+NADH+H^{+} Rightarrow NO_{2}^{-}+NAD^{+} + H_{2}O}]

Nitrite Reductase

[mathrm{NO_{2}^{-}+6Fd_{red}+8H^{+} Rightarrow NH_{4}^{+}+2H_{2}O+6Fd_{ox}}]

Biological Nitrogen Fixation by microorganisms:

Nitrogenase

[mathrm{N_{2}+6e^{-}+6H^{+}+~16ATP+16H_{2}O Rightarrow 2NH_{3}+16ADP+16Pi+16H^{+}}]

Major pathway for ammonia assimilation(=net assimilation in plants, fungi and microorganisms):

Glutamine synthetase (GS)

[mathrm{NH_{3}+Glu+ATP Rightarrow Gln+ADP+Pi}]

Glutamate synthase (= GOGAT)

(not found in animals)

[mathrm{Gln+alpha KG+NAD(P)H+H^{+} Rightarrow 2Glu+ NAD(P)^{+}}]

GS is present in animals as well. GS is also the enzyme responsible for the synthesis of the Gln incorporated into protein in all organisms. In some plants and in humans, Gln is used for intercellular transport of N in a non-toxic form. Ala is also used in mammals for the transport of N from the muscle to the liver.


Haney Test

The Haney Test or Soil Health Test is an integrated approach to soil testing using chemical and
biological soil test data. It is designed to mimic nature’s approach to soil nutrient availability as
best we can in the lab. The Haney Test is designed to work with any soil under any
management scenario because the program asks simple, universally applicable questions.

  1. What is your soil’s condition?
  2. Is your soil in balance?
  3. What can you do to help your soil?
Procedure Outline:

Each soil sample received in the lab is dried at 50o C, ground to pass a 2 mm sieve and weighed into two 50 ml Erlenmeyer flasks (4 g each) and one 50 ml plastic beaker (40 g) that is perforated to allow water infiltration. The 40 g soil sample is analyzed with a 24 hour incubation test at 24oC. This sample is wetted through capillary action by adding 20 ml of DI water to an 8 oz. glass jar and then capped. At the end of 24 hour incubation, the gas inside the jar is analyzed using an infrared gas analyzer (IRGA) Li-Cor 840A (LI-COR Biosciences, Lincoln NE) for CO2-C. The two 4 g samples are extracted with 40 ml of DI water and 40 ml of H3A, respectively. The samples are shaken for 10 minutes, centrifuged for 5 minutes, and filtered through Whatman 2V filter paper. The water and H3A extracts are analyzed on a Lachat 8000 flow injection analyzer (Hach Company, Loveland CO) for NO3-N, NH4-N, and PO4-P. The water extract is also analyzed on a Teledyne-Tekmar Torch C:N analyzer for water-extractable organic C and total N. The H3A extract is also analyzed on a Thermo Scientific ICP-OES instrument for P, K, Mg, Ca, Na, Zn, Fe, Mn, Cu, S and Al.

The methods use nature’s biology and chemistry, in that, the soil analysis is performed using a soil microbial biomass indicator, a soil water extract (nature’s solvent), and H3A extractant, which mimics organic acids produced by living plant roots to temporarily change the soil pH thereby increasing nutrient availability. These organic acids are then broken down by soil microbes since they are an excellent carbon source, which returns the soil pH to its natural, ambient level. The Haney Test doesn’t measure just one thing to arrive at the plant available NPK, we use an integrated approach. For example, if the soil respiration number is 80 ppm CO2 and the organic C: organic N ratio from the soil water extract is above 20:1 we credit no N or P mineralization, as the C:N ratio decreases we credit more release from the organic N and P pools based on CO2 and the lower C:N ratio. For soil with high CO2, low C:N and a high soil health score, we add an additional calculation from the organic N pool, however, we do not credit more N release than we can measure from the organic N and organic P pools.

Nitrogen:

Total N: This number is the total N from the water extract from your soil (in ppm). It contains both inorganic N and organic N sources from your soil.

Inorganic N: This is the combined amount of plant available forms of inorganic N (NO3-N plus NH4-N). NO3-N is the form of N that is easily lost from soil through surface runoff, subsurface leaching, erosion, and in water logged conditions it can revert back to a gas. NH4-H is usually quickly converted to NO3-N by soil microbes but is less susceptible to leaching. The majority of inorganic soil N is in the NO3-N form. If the NO3-N levels are high (above 50 lb/ac), then we would use grasses to convert this easily lost form of N back to the organic form.

Organic N: Organic N is the total water extractable N minus the total water extractable inorganic N in ppm. This form of N should be easily broken down by soil microbes and released to the growing plant providing minimal chance of loss since the N is bound in large organic molecules. This pool represents the amount of potentially mineralizable N in your soil.

Phosphate:

This lists the same type of results as nitrogen but for inorganic P and organic P.

Soil Health:

Soil Respiration 1-day CO2-C: This result is one of the most important numbers in this soil test procedure. This number in ppm is the amount of CO2-C released in 24 hours from soil microbes after your soil has been dried and rewetted (as occurs naturally in the field). This is a measure of the microbial biomass in the soil and is related to soil fertility and the potential for microbial activity. In most cases, the higher the number, the more fertile the soil.

Microbes exist in soil in great abundance. They are highly adaptable to their environment and their composition, adaptability, and structure are a result of the environment they inhabit. They have adapted to the temperature, moisture levels, soil structure, crop and management inputs, as well as soil nutrient content. In short, they are a product of their environment. If this were not true they most likely would have died out long ago, but they didn’t. Since soil microbes are highly adaptive and are driven by their need to reproduce and by their need for acquiring C, N, and P in a ratio of 100: 10: 1 (C:N: P), it is safe to assume that soil microbes are a dependable indicator of soil health. It is clear that carbon is the driver of the soil nutrientmicrobial recycling system. This consistent need sets the stage for a standardized, universal measurement of soil microbial biomass through their respiration activity. Since most soil microbes take in oxygen and release CO2, we can couple this mechanism to their activity. It follows that soil microbial activity is a response to the level of soil quality/fertility in which they find themselves.

Water extractable organic C (WEOC): This number (in ppm) is the amount of organic C extracted from your soil with water. This C pool is roughly 80 times smaller than the total soil organic C pool (% Organic Matter) and reflects the energy source feeding soil microbes. A soil with 3% soil organic matter when measured with the same method (combustion) at a 0-3 inch sampling depth produces a 20,000 ppm C concentration. When we analyze the water extract from the same soil, that number typically ranges from 100-300 ppm C. The water extractable organic C reflects the quality of the C in your soil and is highly related to the microbial activity. On the other hand, % SOM is about the quantity of organic C. In other words, soil organic matter is the house that microbes live in, but what we are measuring is the food they eat (WEOC and WEON).

Water extractable organic N (WEON): This number is the amount of the total water extractable N minus the inorganic N (NH4-N + NO3-N). This N pool is highly related to the water extractable organic C pool and will be easily broken down by soil microbes and released to the soil in inorganic N forms that are readily plant available.

Organic C: Organic N: This number is the ratio of organic C from the water extract to the amount of organic N in the water extract. This C:N ratio is a critical component of the nutrient cycle. Soil organic C and soil organic N are highly related to each other as well as the water extractable organic C and organic N pools. Therefore, we use the organic C:N ratio of the water extract since this is the ratio the soil microbes have readily available to them and is a more sensitive indicator than the soil C:N ratio. A soil C:N ratio above 20:1 generally indicates that no net N and P mineralization will occur, meaning the N and P are “tied up” within the microbial cell until the ratio drops below 20:1. As the ratio decreases, more N and P are released to the soil solution which can be taken up by growing plants. We apply this same mechanism to the water extract, as the C:N falls we credit more N and P mineralization on a sliding scale. We like to see this number between 8:1 and 15:1.

Soil Health Calculation: This number is calculated as 1-day CO2-C/10 plus WEOC/50 plus WEON/10 to include a weighted contribution of water extractable organic C and organic N. It represents the overall health of your soil system. It combines 5 independent measurements of your soil’s biological properties. The calculation looks at the balance of soil C and N and their relationship to microbial activity. This soil health calculation number can vary from 0 to more than 50. We like to see this number above 7 and increase over time. This number indicates your current soil health and what it needs to reach its highest sustainable state. Keeping track of this soil health number will allow you to gauge the effects of your management practices over the years.

Cover Crop Mix: This is a suggested cover crop planting mix based on your soil test data. This is a recommendation of what you can do to increase your soil health number, but it is not what you have to do. It is designed to provide your soil with a multi-species cover crop to help you improve soil health and thus improve the fertility of your soil.

Available N-P-K:

These numbers represent the amount of N, P2O5, and K2O present in your soil in lb/ac. The numbers include the inorganic NH4-N, NO3-N, and PO4-P from the H3A extractant, as well as the amount of N and P that the soil microbes will provide based on soil microbial respiration, the organic C: organic N ratio, and the N and P from the organic pools.

Nutrient value per acre: Current fertilizer prices are multiplied by the nutrients present in your soil. This is the value in dollars of nutrients currently in your soil.

NO3-N Only (traditional evaluation) lbs per acre: This value represents the amount of N in your soil when testing for only nitrate, similar to common soil tests.

Haney Test N Evaluation lbs per acre: This is the amount of available nitrogen measured using the Haney Test and is the same as the available N value on the report.

Nitrogen Difference lbs per acre: This number represents the difference in the amount of nitrogen we found using the Haney Test compared to the NO3-N only approach.

Nitrogen savings per acre: This value represents the amount of nitrogen saved in dollars per acre when using the Haney Test compared to traditional testing measuring only NO3-N.

Fertilizer Recommendations: This table provides recommended values for various plant essential nutrients in lbs per acre that your soil needs to produce your stated yield goal for a specific crop. You must provide a crop and yield goal for each sample in order to get recs.

Additional information is available on the website at www.wardlab.com and new information may be added as it becomes available. Any questions regarding soil health testing may be directed to [email protected]

Sampling Information (H3A)

Listed here are general guidelines to sample for the Haney Test or Soil Health Test:

If combining Haney analysis with PLFA, please refer to the PLFA sample submittal instructions and follow those guidelines for submitting one sample for both tests.


Plants absorb nitrogen from the soil in the form of nitrate (NO3 − ) and ammonium (NH4 + ). In aerobic soils where nitrification can occur, nitrate is usually the predominant form of available nitrogen that is absorbed. [1] [2] However this is not always the case as ammonia can predominate in grasslands [3] and in flooded, anaerobic soils like rice paddies. [4] Plant roots themselves can affect the abundance of various forms of nitrogen by changing the pH and secreting organic compounds or oxygen. [5] This influences microbial activities like the inter-conversion of various nitrogen species, the release of ammonia from organic matter in the soil and the fixation of nitrogen by non-nodule-forming bacteria.

Ammonium ions are absorbed by the plant via ammonia transporters. Nitrate is taken up by several nitrate transporters that use a proton gradient to power the transport. [6] [7] Nitrogen is transported from the root to the shoot via the xylem in the form of nitrate, dissolved ammonia and amino acids. Usually [8] (but not always [9] ) most of the nitrate reduction is carried out in the shoots while the roots reduce only a small fraction of the absorbed nitrate to ammonia. Ammonia (both absorbed and synthesized) is incorporated into amino acids via the glutamine synthetase-glutamate synthase (GS-GOGAT) pathway. [10] While nearly all [11] the ammonia in the root is usually incorporated into amino acids at the root itself, plants may transport significant amounts of ammonium ions in the xylem to be fixed in the shoots. [12] This may help avoid the transport of organic compounds down to the roots just to carry the nitrogen back as amino acids.

Nitrate reduction is carried out in two steps. Nitrate is first reduced to nitrite (NO2 − ) in the cytosol by nitrate reductase using NADH or NADPH. [7] Nitrite is then reduced to ammonia in the chloroplasts (plastids in roots) by a ferredoxin dependent nitrite reductase. In photosynthesizing tissues, it uses an isoform of ferredoxin (Fd1) that is reduced by PSI while in the root it uses a form of ferredoxin (Fd3) that has a less negative midpoint potential and can be reduced easily by NADPH. [13] In non photosynthesizing tissues, NADPH is generated by glycolysis and the pentose phosphate pathway.

In the chloroplasts, [14] glutamine synthetase incorporates this ammonia as the amide group of glutamine using glutamate as a substrate. Glutamate synthase (Fd-GOGAT and NADH-GOGAT) transfer the amide group onto a 2-oxoglutarate molecule producing two glutamates. Further transaminations are carried out make other amino acids (most commonly asparagine) from glutamine. While the enzyme glutamate dehydrogenase (GDH) does not play a direct role in the assimilation, it protects the mitochondrial functions during periods of high nitrogen metabolism and takes part in nitrogen remobilization. [15]

PH and Ionic balance during nitrogen assimilation Edit

Every nitrate ion reduced to ammonia produces one OH − ion. To maintain a pH balance, the plant must either excrete it into the surrounding medium or neutralize it with organic acids. This results in the medium around the plants roots becoming alkaline when they take up nitrate.

To maintain ionic balance, every NO3 − taken into the root must be accompanied by either the uptake of a cation or the excretion of an anion. Plants like tomatoes take up metal ions like K + , Na + , Ca 2+ and Mg 2+ to exactly match every nitrate taken up and store these as the salts of organic acids like malate and oxalate. [16] Other plants like the soybean balance most of their NO3 − intake with the excretion of OH − or HCO3 − . [17]

Plants that reduce nitrates in the shoots and excrete alkali from their roots need to transport the alkali in an inert form from the shoots to the roots. To achieve this they synthesize malic acid in the leaves from neutral precursors like carbohydrates. The potassium ions brought to the leaves along with the nitrate in the xylem are then sent along with the malate to the roots via the phloem. In the roots, the malate is consumed. When malate is converted back to malic acid prior to use, an OH − is released and excreted. (RCOO − + H2O -> RCOOH +OH − ) The potassium ions are then recirculated up the xylem with fresh nitrate. Thus the plants avoid having to absorb and store excess salts and also transport the OH − . [18]

Plants like castor reduce a lot of nitrate in the root itself, and excrete the resulting base. Some of the base produced in the shoots is transported to the roots as salts of organic acids while a small amount of the carboxylates are just stored in the shoot itself. [19]

Nitrogen use efficiency (NUE) is the proportion of nitrogen present that a plant absorbs and uses. Improving nitrogen use efficiency and thus fertilizer efficiency is important to make agriculture more sustainable, [20] by reducing pollution and production cost and increasing yield. Worldwide, crops generally have less than 50% NUE. [21] Better fertilizers, improved crop management, [21] and genetic engineering [20] can increase NUE. Nitrogen use efficiency can be measured at the ecosystem level or at the level of photosynthesis in leaves, when it is termed photosynthetic nitrogen use efficiency (PNUE). [22] [23]


MATERIALS AND METHODS

Uptake of nitrate, ammonium and glycine by Lolium perenne from single and mixed source solutions

Within a laminar airflow cabinet, seeds of Lolium perenne L. (Emorsgate Seeds, King's Lynn, UK) were surface-sterilized using 1% (v/v) peracetic acid but otherwise as described in Thornton (2004 ). Following the final water rinse the moist seeds were placed aseptically within glass Petri dishes sealed with Parafilm ‘M’ (American National Can, Chicago, IL, USA) and kept at 20 °C in the dark. After 5 d, when the seeds had germinated, they were transferred aseptically onto discs of Tygan mesh at a density of approximately 20 seeds per disc individual discs were then placed over 1.0 L of deionized water in sterile culture vessels ( Thornton 2001 ). Sixty culture vessels were placed, totally randomized, within a controlled environment room (Conviron, Winnipeg, Canada) at 20 °C in the dark. The following day a 16-h photoperiod of 290 ± 30 µmol m −2 s −1 photosynthetically active radiation at plant height was introduced. At the same time the water in the vessels was replaced by a complete nutrient solution, as described by Thornton & Bausenwein (2000 ) except that N was supplied as 1 mol m −3 NH4NO3 (2 mol m −3 N), sterilized by passing it through a 0.2-µm cellulose nitrate filter (Whatman, Maidstone, UK). The temperature of the controlled environment room was adjusted to maintain a constant 21 °C within the culture vessels.

Five days after germination, half the vessels were transferred to a second controlled environment room in which all conditions were identical to the first with the exception that the temperature of the room was adjusted to maintain a constant temperature of 11 °C within the culture vessels. The nutrient solution in all vessels was renewed aseptically within the laminar airflow 8 and 14 d after germination. Because N uptake varies diurnally ( Ourry et al. 1996 Macduff et al. 1997 ), continuous light was introduced to all vessels 19 d after germination to minimize any effect of the timing of harvest (which took 5 h) on the uptake. Some roots, but especially in vessels at the lower temperature, developed a reddish purple colour. This observed pigmentation was most probably due to anthocyanin production consistent with its putative role in ameliorating cold-temperature stress ( Chalker-Scott 1999 ). The vessels within each controlled environment room were subsequently arranged in five replicate blocks. Vessels containing plants with the whitest roots were designated to the first block and vessels containing roots of increasing redness allocated to subsequent blocks.

Twenty days after germination, the nutrient solutions used for growth of the plants were replaced by ‘uptake’ solutions the growth and uptake solutions were identical to each other in all aspects except N. In three uptake solutions, N was supplied as a single source either: (1) 0.33 mol m −3 (NH4)2SO4 with a 15 N abundance of 5.06 atom % (2) 0.66 mol m −3 KNO3 with a 15 N abundance of 5.19 atom % or (3) 0.66 mol m −3 glycine with a 15 N abundance of 5.08 atom %. In a further three uptake solutions, N was supplied as a mixture containing 0.33 mol m −3 (NH4)2SO4 (i.e. 0.66 mol m −3 NH4 + ) and 0.66 mol m −3 KNO3 and 0.66 mol m −3 glycine (2 mol m −3 N) in which only one form of the N was labelled with 15 N, either: (1) NH4 + at 30.26 atom % (2) NO3 – at 30.44 atom % or (3) glycine at 30.02 atom %. Plants remained at the temperature of their growth in the uptake solution for 24 h, after which they were harvested.

At harvest, the roots of the intact plants were dipped in fresh 1 mol m −3 CaSO4 solution at 5 °C for 1 min and blotted dry. Plants were then separated into root and shoot material, the original seed being discarded. Samples were weighed fresh and then frozen and stored at −80 °C. The frozen samples were freeze-dried (Supermodulyo Edwards High Vacuum International, Crawley, UK), reweighed then ball milled (Retsch MM2000 Haan, Germany). The total N and 15 N concentrations of weighed aliquots of the ball-milled plant material were determined using a TracerMAT continuous flow mass spectrometer (Finnigan MAT, Hemel Hempstead, UK). The uptake of the 15 N labelled compounds was determined using the equations of Millard & Nielsen (1989 ). From the observed rates of uptake (see Results) it was estimated that depletion of any individual form of N from the uptake solution ranged from 7% (nitrate in the mixed nutrient solution at 11 °C) to 25% (ammonium in the single source solution at 21 °C).

Further 15 mg aliquots of the milled plant material were extracted with 3 cm 3 of 80% (v/v) ethanol for 1 h with occasional shaking. The solution was then centrifuged at 3500 g for 15 min. The supernatant was retained and the pellet re-suspended in 1.5 cm 3 of 80% ethanol for a further 1 h, then centrifuged at 3500 g for 15 min. The supernatants were combined, blow-dried in a stream of N2 gas, then re-suspended once more in 1 cm 3 of 0.1 kmol m −3 HCl. Following a 10-min centrifugation at 10 000 g, the supernatant was poured onto cation exchange columns of 2 cm 3 bed volume of Dowex 50WX8-200 in the H + form (Sigma-Aldrich, St Louis, MO, USA). The columns were washed with 20 cm 3 of deionized water and the amino acids eluted with 20 cm 3 of 4 kmol m −3 NH4OH. The eluate was blown overnight with a stream of N2 gas to remove NH3, then freeze-dried. Amino acids in the resultant extracts were converted to their t-butyldimethylsilyl derivatives and the concentration and 15 N abundance of the individual amino acids determined by gas chromatography mass spectrometry (GC-MS) as described by Millard et al. (1998 ).

The proportions of N taken up as different N-forms over the 24 h 15 N labelling period were calculated by assuming that plants in the various N source treatments were identical. This assumption is reasonable since all plants were raised on the same N source, NH4NO3, before the labelling period. Data from the three single source treatments were combined. For example, if 9.8, 23 and 4.5 mg N g −1 DW were taken up as nitrate, ammonium and glycine, respectively, when these were supplied to different plants as single N-sources, the corresponding proportional uptakes would be 0.26, 0.62 and 0.12. Similarly, data were combined across the three 15 N labelling schemes to calculate proportional uptake from the mixed N sources.

Differences between treatments were assessed by analysis of variance using G enstat 7th edition, Release 7.1 © Lawes Agricultural Trust (IACR-Rothamsted, Harpenden, UK). Results of the proportion of total uptake by a particular form of N were subject to angular arc-sine transformation before analysis. Since transformation did not alter the interpretation of results, untransformed data are presented for clarity.


Steps Involved in Nitrogen Cycle | Ecology

The following points highlight the six main steps involved in nitrogen cycle. The steps are: 1. Nitrogen Fixation 2. Nitrogen Assimilation 3. Ammonification 4. Nitrification 5. Denitriflcation 6. Sedimentation.

Nitrogen Cycle: Step # 1. Nitrogen Fixation:

Conversion of free nitrogen of atmosphere into the biologically acceptable form or nitrogenous compounds is referred to as nitrogen flxation.

This process is of two types:

(i) Physicochemical or non-biological nitrogen fixation, and

(ii) Biological nitrogen fixation.

In physico-chemical process, the atmospheric nitrogen combines with oxygen (as ozone) during lightning or electrical discharges in the clouds and produces different nitrogen oxides.

The equations are as follows:

These nitrogen oxides get dissolved in rain water, and on reaching earth surface they react with mineral compounds to form nitrates and other nitrogenous compounds:

During combustion of various types, some nitrogenous compounds are formed, which are washed down along with rain water.

Biological nitrogen fixation is carried out by certain prokaryotes. The cyanobacteria (blue- green algae) fix significant amounts of nitrogen in the oceans, lakes and soils.

Symbiotic bacteria (Rhizobium) inhabiting the root rodules of legumes and symbiotic cyanobacteria, such as Nostoc, Anabaena, etc., found in free state, or in thalli of Anthoceros (bryophyte), Azolla (water fern), coralloid roots of Cycas (gymnosperm) fix atmospheric nitrogen.

Certain free living nitrogen fixing bacteria, such as Azotobacter, Clostridium, Beijerinckia, etc., also fix free nitrogen of atmosphere in the soil. Frankia, an actinomycetous fungus found in the roots of higher plants, such as Alnus and Casuarina, also fix nitrogen.

Nitrogen fixing organisms combine the gaseous nitrogen of atmosphere with hydrogen obtained from respiratory pathway to form ammonia, which then reacts with organic acids to form amino acids.

Biological nitrogen fixation is the major source of fixed nitrogen up-to 140 – 700 mg/m 2 year as against 35 mg/m 2 /year by electrical discharge and photochemical fixation.

Nitrogen Cycle: Step # 2. Nitrogen Assimilation:

Inorganic nitrogen in the form of nitrates, nitrites and ammonia is absorbed by the green plants and converted into nitrogenous organic compounds. Nitrates are first converted into ammonia which combines to organic acids to form amino acids. Aminoacids are used in the synthesis of proteins, enzymes, chlorophylls, nucleic acids, etc.

Animals derive their nitrogen requirement from the plant proteins. Plant proteins are not directly utilised by the animals. They are first broken down into amino-acids during digestion and then the amino-acids are absorbed and manipulated into animal proteins, nucleic acids, etc.

Nitrogen Cycle: Step # 3. Ammonification:

The dead organic remains of plants and animals and excreta of animals are acted upon by a number of microorganisms, especially actinomycetes and bacilli, such as Bacillus ramosus, B. vulgaris, etc. These organisms utilise organic compounds in their metabolism and release ammonia. This process is called ammonification. After meeting their own metabolic requirement, these microbes release the excess ammonia in the soil.

Nitrogen Cycle: Step # 4. Nitrification:

In next step of ammonia formation, ammonia is converted into nitrate by a group of chemo- autotrophic bacteria through a two-step process called nitrification.

Certain bacteria such as Nitrosomonas, Nitrococcus and Nitrospira in oceans and soils convert ammonia into nitrites and then nitrites into nitrates. These bacteria primarily use the energy of dead organic matter in their metabolism.

The equation is as follows:

Conversion of nitrites to nitrates is brought about by several microbes, such as Penicillium (a fungus), Nitrobacter, etc.

Some nitrates are also made available through weathering of nitrate containing rocks.

Nitrogen Cycle: Step # 5. Denitriflcation:

Ammonia and nitrates are converted into free nitrogen by certain microbes. This process is referred to as denitriflcation. Pseudomonas, the most common denitrifying bacterium, thrives best under poorly aerated and detritus-rich conditions. Denitrifying bacteria transform nitrate nitrogen to nitrous and nitric oxides, and ultimately to gaseous nitrogen, which goes to atmosphere. ‘

Denitrification by denitrifying bacteria.

Nitrogen Cycle: Step # 6. Sedimentation:

Nitrates of the soil are washed away to the sea or leached deep into the earth along with percolating water. Nitrates thus lost from the soil surface are locked up in the rocks. This process is called sedimentation of nitrogen. Nitrogen of rock is released only when the rocks are exposed and weathered.

Thus a large part of nitrogen is fixed up and stored up in plants, animals and microbes. Most higher plants absorb nitrate from the soil the absorbed nitrate is ultimately converted to organic nitrogen. A fraction of nitrogen incorporated in plant tissues is used by consumers, and ultimately all dead remains convert into detritus and used by decomposers. Thus, complex nitrogen cycle completes.


Current understanding of sulfur assimilation metabolism to biosynthesize l -cysteine and recent progress of its fermentative overproduction in microorganisms

To all organisms, sulfur is an essential and important element. The assimilation of inorganic sulfur molecules such as sulfate and thiosulfate into organic sulfur compounds such as l -cysteine and l -methionine (essential amino acid for human) is largely contributed by microorganisms. Of these, special attention is given to thiosulfate (S2O3 2− ) assimilation, because thiosulfate relative to often utilized sulfate (SO4 2− ) as a sulfur source is proposed to be more advantageous in microbial growth and biotechnological applications like l -cysteine fermentative overproduction toward industrial manufacturing. In Escherichia coli as well as other many bacteria, the thiosulfate assimilation pathway is known to depend on O-acetyl- l -serine sulfhydrylase B. Recently, another yet-unidentified CysM-independent thiosulfate pathway was found in E. coli. This pathway is expected to consist of the initial part of the thiosulfate to sulfite (SO3 2− ) conversion, and the latter part might be shared with the final part of the known sulfate assimilation pathway [sulfite → sulfide (S 2− ) → l -cysteine]. The catalysis of thiosulfate to sulfite is at least partly mediated by thiosulfate sulfurtransferase (GlpE). In this mini-review, we introduce updated comprehensive information about sulfur assimilation in microorganisms, including this topic. Also, we introduce recent advances of the application study about l -cysteine overproduction, including the GlpE overexpression.

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Abbreviations

Abdallah, M., Etienne, P., Ourry, A., Meuriot, F.: Do initial S reserves and mineral S availability alter leaf S-N mobilization and leaf senescence in oilseed rape? — Plant Sci. 180: 511–520, 2011.

Avila-Ospina, L., Marmagne, A., Talbotec, J., Krupinska, K., Masclaux-Daubresse, C.: The identification of new cytosolic glutamine synthetase and asparagine synthetase genes in barley (Hordeum vulgare L.) and their expression during leaf senescence. — J. exp. Bot. 66: 213–226, 2015.

Bazargani, M.M., Hajirezaei, M.-R., Salekdeh, G.H., Bushehri, A-A.S., Falahati-Anbaran, M., Moradi, F., Naghavi, M.-R., Ehdaie, B.: A view on the role of metabolites in enhanced stem reserves remobilization in wheat under drought during grain filling. — Aust. J. Crop Sci. 6: 1613–1623, 2012.

Bernard, S.M., Habash D.Z.: The importance of cytosolic glutamine synthetase in nitrogen assimilation and recycling. — New Phytol. 182: 608–620, 2009.

Bradford, M.M.: A rapid and sensitive method for the quantification of microgram quantities of protein utilizing the principle of protein dye-binding. — Anal. Biochem. 72: 248–254, 1976.

Brugière, N., Dubois, F., Limami, A.M., Lelandais, M., Roux, Y., Sangwan, R.S., Hirel, B.: Glutamine synthetase in the phloem plays a major role in controlling proline production. — Plant Cell 11: 1995–2011, 1999.

Buchanan-Wollaston, V., Earl, S., Harrison, E., Mathas, E., Navabpour, S., Page, T., Pink, D.: The molecular analysis of leaf senescence — a genomics approach. — Plant Biotech. J. 1: 3–22, 2003.

Caputo, C., Barneix, A.J.: Export of amino acids to the phloem in relation to N supply in wheat. — Physiol. Plant. 101: 853–860, 1997.

Caputo, C., Fatta, N., Barneix, A.J.: The amino acid export to the phloem is altered in wheat plants lacking the short arm of chromosome 7B. — J. exp. Bot. 52: 1761–1768, 2001.

Caputo, C., Criado, M.V., Roberts, I.N., Gelso, M.A., Barneix, A.J.: Regulation of glutamine synthetase 1 and amino acids transport in the phloem of young wheat plants. — Plant Physiol. Biochem. 47: 335–342, 2009.

Cataldo, D.A., Haroon, M., Schrader, L.E., Youngs, V.L.: Rapid colorimetric determination of nitrate in plant tissue by nitration of salicylic acid. — Commun. Soil Sci. Plant Anal. 6: 71–80, 1975.

Chen, P., Wang, L.: Effects of sulfur deficiency on photosynthesis and chlorophyll fluorescence of Citrus sinensis Osbeck leaves. — Chin. J. Ecol. 05, 2006.

Cren, M., Hirel, B.: Glutamine synthetase in higher plants: regulation of gene and protein expression from the organ to the cell. — Plant Cell Physiol. 40: 1187–1193, 1999.

Dalling, M.J.: The physiological basis of nitrogen redistribution during grain filling in cereals — In: Harper, J.D, Schrader, L.E., Howell, R.W. (ed.): Exploitation of Physiological and Genetic Variability to Enhance Crop Productivity. Pp. 55–69. Waverly Press, Baltimore 1985.

De Bona, F.D., Fedoseyenko, D., Von Wirén, N., Monteiro, F.A.: Nitrogen utilization by sulfur-deficient barley plants depends on the nitrogen form. — Environ. exp. Bot. 74: 237–244, 2011.

Dubousset, L., Abdallah, M., Desfeux, A.S., Etienne, P., Meuriot, F., Hawkesford, M.J., Gombert, J., Ségura, R., Bataillé, M-P., Rezé, S., Bonnefoy, J., Ameline, A.F., Ourry, A., Le Dily, F., Avice, J.C.: Remobilization of leaf S compounds and senescence in response to restricted sulphate supply during the vegetative stage of oilseed rape are affected by mineral N availability. — J. exp. Bot. 60: 3239–3253, 2009.

Edwards, J.W., Coruzzi, G.W.: Photorespiration and light act in concert to regulate the expression of the nuclear gene for chloroplast glutamine synthetase. — Plant Cell 1: 241–248, 1989.

Goodall, A.J., Kumar, K., Tobin, A.K.: Identification and expression analyses of cytosolic glutamine synthetase genes in barley (Hordeum vulgare L.). — Plant Cell Physiol. 54: 492–505, 2013.

Hesse, H., Nikiforova, V., Gakière, B., Hoefgen, R.: Molecular analysis and control of cysteine biosynthesis: integration of nitrogen and sulphur metabolism. — J. exp. Bot. 55: 1283–1292, 2004.

Kohl, S., Hollmann, J., Blattner, F.R., Radchuk, V., Andersch, F., Steuernagel, B., Schmutzer, T., Scholz, U., Krupinska, K., Weber, H., Weschke, W.: A putative role for amino acid permeases in sink-source communication of barley tissues uncovered by RNA-seq. — BMC Plant Biol. 12: 154. doi: 10.1186/1471-2229-12-154, 2012.

Larher, F., Aziz, A., Deleu, C., Lemesle, P., Ghaffar, A., Bouchard, F., Plasman, M.: Suppression of the osmoinduced proline response of rapeseed leaf discs by polyamines. — Physiol. Plant. 102: 139–147, 1998.

Lewandowska, M., Sirko, A.: Recent advances in understanding plant response to sulfur-deficiency stress. — Acta biochim. polon. 55: 457–471, 2008.

Lunde, C., Zygadlo, A., Simonsen, H.T., Nielsen, P.L., Blennow, A., Haldrup, A.: Sulfur starvation in rice: the effect on photosynthesis, carbohydrate metabolism, and oxidative stress protective pathways. — Physiol. Plant. 134: 508–521, 2008.

Martin, A., Lee, J., Kichey, T., Gerentes, D., Zivy, M., Tatout, C., Dubois, F., Balliau, T., Valot, B., Davanture, M., Tercé-Laforgue, T., Quilleré, I., Coque, M., Gallais, A., Gonzales-Moro, M-B., Bethencourt, L., Habash, D.Z., Lea, P.J., Charcosset, A., Perez, P., Murigneux, A., Sakakibara, H., Edwards, K.J., Hirel, B.: Two cytosolic glutamine synthetase isoforms of maize are specifically involved in the control of grain production. — Plant Cell. 18: 3252–3274, 2006.

Miflin, B.J., Habash, D.Z.: The role of glutamine synthetase and glutamate dehydrogenase in nitrogen assimilation and possibilities for improvement in the nitrogen utilization of crops. — J. exp. Bot. 53 (Inorganic Nitrogen Assimilation Special Issue): 979–987, 2002.

Nikiforova, V.J., Gakiére, B., Kempa, S., Adamik, M., Willmitzer, L., Hesse, H., Hoefgen, R.: Towards dissecting nutrient metabolism in plants: a systems biology case study on sulphur metabolism. — J. exp. Bot. 55 (Sulphur Metabolism in Plants Special Issue): 1861–1870, 2004.

Nikiforova, V.J., Kopka, J., Tolstikov, V., Fiehn, O., Hopkins, L., Hawkesford, M.J., Hesse, H., Hoefgen, R.: Systems rebalacing of metabolism in response to sulfur deprivation, as revealed by metabolome analysis of Arabidospsis plants. — Plant Physiol. 138: 304–318, 2005.

Pratelli, R., Pilot, G.: Regulation of amino acid metabolic enzymes and transporters in plants. — J. exp. Bot. 65: 5535–5556, 2014.

Scherer, H.W.: Sulphur in crop production. — Eur. J. Agron. 14: 81–111, 2001.

Sorin, E., Etienne, P., Maillard, A., Zamarreño, A-M., Garcia-Mina, J-M., Arkoun, M., Jamois, F., Cruz, F., Yvin, J-C., Ourry, A.: Effect of sulphur deprivation on osmotic potential components and nitrogen metabolism in oilseed rape leaves: identification of a new early indicator. — J. exp. Bot. 66: 6175–6189, 2015.

Tabuchi, M., Sugiyama, K., Ishiyama, K., Inoue, E., Sato, T., Takahashi, H., Yamaya, T.: Severe reduction in growth rate and grain filling of rice mutants lacking OsGS1 1, a cytosolic glutamine synthetase1 1. — Plant J. 42: 641–651, 2005.

Tegeder, M., Rentsch, D.: Uptake and partitioning of amino acids and peptide. — Mol. Plant. 3: 997–1011, 2010.

Tegeder, M.: Transporters for amino acids in plant cells: some functions and many unknowns. — Curr. Opin. Plant Biol. 15: 315–321, 2012.

Veliz, C.G., Criado, M.V., Roberts, I.N., Echeverria, M., Prystupa, P., Prieto, P., Gutierrez Boem, F.H., Caputo, C.: Phloem sugars and amino acids as potential regulators of hordein expression in field grown malting barley (Hordeum vulgare L.). — J. Cereal Sci. 60: 433–439, 2014.

Wallsgrove, R.M., Turner, J.C., Hal, N.P., Kendall, A.C., Bright, S.W.: Barley mutants lacking chloroplast glutamine synthetase — biochemical and genetic analysis. — Plant Physiol. 83: 155–158, 1987.

Weibull, J., Ronquist, F., Brishammar, S.: Free amino acid composition of leaf exudates and phloem sap: a comparative study in oats and barley. — Plant Physiol. 92: 222–226, 1990.

Winter, H., Lohaus, G., Heldt, H.W.: Phloem transport of amino acids in relation to their cytosolic levels in barley leaves. — Plant Physiol. 99: 996–1004, 1992.

Yamaya, T., Kusano, M.: Evidence supporting distinct functions of three cytosolic glutamine synthetases and two NADH-glutamate synthases in rice. — J. exp. Bot. 65: 5519–5525, 2014.


Relationship of Nitrogen Use Efficiency with the Activities of Enzymes Involved in Nitrogen Uptake and Assimilation of Finger Millet Genotypes Grown under Different Nitrogen Inputs

Nitrogen responsiveness of three-finger millet genotypes (differing in their seed coat colour) PRM-1 (brown), PRM-701 (golden), and PRM-801 (white) grown under different nitrogen doses was determined by analyzing the growth, yield parameters and activities of nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase GOGAT, and glutamate dehydrogenase (GDH) at different developmental stages. High nitrogen use efficiency and nitrogen utilization efficiency were observed in PRM-1 genotype, whereas high nitrogen uptake efficiency was observed in PRM-801 genotype. At grain filling nitrogen uptake efficiency in PRM-1 negatively correlated with NR, GS, GOGAT activities whereas it was positively correlated in PRM-701 and PRM-801, however, GDH showed a negative correlation. Growth and yield parameters indicated that PRM-1 responds well at high nitrogen conditions while PRM-701 and PRM-801 respond well at normal and low nitrogen conditions respectively. The study indicates that PRM-1 is high nitrogen responsive and has high nitrogen use efficiency, whereas golden PRM-701 and white PRM-801 are low nitrogen responsive genotypes and have low nitrogen use efficiency. However, the crude grain protein content was higher in PRM-801 genotype followed by PRM-701 and PRM-1, indicating negative correlation of nitrogen use efficiency with source to sink relationship in terms of seed protein content.

1. Introduction

Cereal grains are considered to be one of the most important sources of dietary proteins, carbohydrates, vitamins, minerals, and fiber for people all over the world. Finger millet commonly referred as ragi or mandua ranks fourth in importance among millets in the world after sorghum (Sorghum bicolor), pearl millet (Pennisetum glaucum), and foxtail millet (Setaria italica). Finger millet, Eleusine coracana (L.) Gaertn subsp. coracana, belongs to family Poaceae, subfamily Chloridoideae, and is considered to be a native crop of Central Africa [1]. Finger millet is grown mainly by subsistence farmers and serves as a food security crop [2] because of its high nutritional value and excellent storage qualities. Since finger millet capitalizes on low nitrogen inputs, it could be considered as high nitrogen efficient crop. Thus, it is quite pertinent and promising to study the biochemical mechanism(s) associated with nitrogen use efficiency using this crop as model system.

Nitrogen use efficiency (NUE) at the plant level is its ability to utilize the available nitrogen (N) resources to optimize its productivity. This includes nitrogen uptake and assimilatory processes, redistribution within the cell and balance between storage and current use at the cellular and whole plant level [3, 4]. Nitrogen use efficiency (NUE) for crop plants is of great concerns throughout the world. Burgeoning population of world needs crop genotypes responding to higher nitrogen and showing direct relationship to yield with use of nitrogen inputs, that is, high nitrogen responsive genotypes. However, for fulfilling the high global demand of organic produce, it requires the low nitrogen responsive genotypes with greater NUE and grain yields. Nitrogen use efficiency in plants is a complex quantitative trait that involves many genes and depends on a number of internal and external factors in addition to soil nitrogen availability, such as photosynthetic carbon fixation to provide precursors required for amino acid biosynthesis or respiration to provide energy. The assimilation of inorganic nitrogen into organic form has marked effect on plant productivity, biomass, and crop yield [5, 6]. In all higher plants, inorganic nitrogen is first reduced to ammonia prior to incorporation into organic form [7]. Reduction of nitrate occurs in two distinct reactions catalyzed by different enzymes. The first reaction occurs in cytosol catalyzed by nitrate reductase, which reduces nitrate to nitrite [8]. Nitrite arising in cytosol from nitrate reductase action is transported into chloroplasts in leaves where nitrite is further reduced by the action of nitrite reductase to ammonium ions [7]. Ammonia is assimilated into organic form as glutamine and glutamate, which serves as the nitrogen donors in the biosynthesis of essentially all amino acids, nucleic acids, and other nitrogen containing compounds such as chlorophyll. The individual isoenzymes of glutamine synthetase (GS, E.C.6.3.1.2), glutamate synthase (NADH-GOGAT-E.C.1.4.1.14, FD-GOGAT-E.C.1.4.7.1), and glutamate dehydrogenase (NADH-GDH: EC.1.4.1.2 NADPH-GDH: E.C.1.4.1.4) have been proposed to play important role in three major ammonium assimilation processes: primary nitrogen assimilation, reassimilation of photorespiratory ammonia, and reassimilation of “recycled” nitrogen [7]. Glutamine and glutamate can then be used to form aspartate and asparagines, and these four amino acids are used to translocate organic nitrogen from sources to sinks [9, 10]. The enzymes involved in the primary assimilation of ammonium into these four N-transport amino acids Glu/Gln and Asp/Asn are glutamine synthetase (GS), glutamate synthase (GOGAT), aspartate amino transferase (AAT), and asparagines synthetase (AS). The importance of glutamate dehydrogenase (GDH) in higher plant N metabolism is still controversial, as it has never been clearly demonstrated that the enzyme plays a significant role either in ammonia assimilation or carbon recycling in plants [11, 12]. Moreover, the role of GDH in N management and recycling has recently been reviewed in a number of whole-plant physiological studies performed on tobacco [12] and maize [13].

Since, from both economical and ecological point of view, agricultural practices are going towards extensive systems using lower N fertilizers, a better knowledge of physiological basis of nitrogen use efficiency (NUE) in economically important crop such as finger millet is required. Although finger millet is highly nitrogen use efficient crop yet, there is a wide variation across the genotypic level. Thus, the development of finger millet that can make the best use of N in low-nitrogen soils is essential for the sustainability of agriculture [14]. This highly complex objective requires a deep understanding of the physiological and biochemical responses of finger millet genotypes to different nitrogen levels. In the present investigation, attempts were made to understand the mechanisms associated with NUE and the nitrogen uptake and assimilatory enzymes in finger millet grown under different nitrogen conditions.

2. Material and Methods

2.1. Plant Material and Nitrogen Treatments

Three finger millet (Eleusine coracana) genotypes (differing in their seed coat colour) PRM-1 (brown), PRM-701 (golden), and PRM-801 (white) were grown in pot conditions. For each finger millet variety, four nitrogen treatments were given, namely, high nitrogen dose (60 kg/ha), normal nitrogen dose (40 kg/ha), low nitrogen treatments (20 kg/ha) and farmyard, FYM (7.5 tonnes/hectare) along with control (no nitrogen added). Thus, five soil conditions were used. Nitrogen was applied through urea at three intervals, namely, 50% at the time of sowing, 25% at five leaf stage (30 days after sowing), 25% at the time of flowering/post anthesis. All the pots and control received a basal dose of 20 kg/ha of each muriate of potash and single superphosphates.

2.2. Growth Parameters

The plant height and leaf area (LICOR-3000 leaf area meter) were measured at the vegetative stage (40 days after sowing) and the flowering stage. SPAD value was noted by chlorophyll meter SPAD-502 at vegetative stage (40 days after sowing), the flowering stage, and grain filling stages. The dry matter and grain yield were noted at the time of harvest. Heading date was determined by counting the number of days from sowing to 50% of spikes fully emerged from the boot.

2.3. Extraction and Assay of Nitrogen Uptake and Ammonium Assimilation Enzymes

The four enzymes, namely, NR, GS, GOGAT, and GDH, were assayed in freshly harvested flag leaf at three different developmental stages of finger millet genotypes. The protein was determined from all of the enzyme extracts [15]. All the assays were done with three replications. Specific activity of an enzyme has been defined as μmol of product formed per mg protein.

2.3.1. Nitrate Reductase (NR)

The nitrate reductase (NR) activity was estimated by using the method described by Hageman and Hucklesby, 1971 [16]. 500 mg of freshly harvested flag leaf tissue were cut into small pieces and were transferred into test tubes containing 3 mL of each 0.2 M potassium phosphate buffer (pH 7.5), and 0.4 M potassium nitratewhich were then incubated in dark at 33°C for 30 min. Add 0.2 mL of above extract after incubation in separate test tube containing 1 mL distilled water. Add 1.2 mL (1 : 1 v/v) mixture of NED (0.1% w/v) and sulphanilamide (1% (w/v) in 3 N HCl) and keep in darkness for 15 min for pink colour development. The absorbance was measured at 540 nm with the help of spectrophotometer using distilled water as blank, and the amount of nitrite present was found out by comparing with the standard curve.

2.3.2. Glutamine Synthetase (GS)

The extraction buffer included, 10 mM-Tris HCl (pH 7.6), 1 mM-MgCl2, 1 mM-EDTA, and 1 mM-2 mercaptoethanol. Leaves (2 g) were grinded using liquid N2 in the presence of cover slips followed by centrifugation at 12,000 xg for 30 min at 4°C [17]. Supernatant was collected and stored at −20°C. The assays were carried out by continuous spectrophotometric rate determination method.

2.3.3. Glutamate Synthase (GOGAT)

Activity of GOGAT was determined in enzyme preparation described for GS. Standard assay mixture contained 40 mM potassium phosphate buffer (pH 7.5), 10 mM L-glutamine, 10 mM 2-oxoglutarate, 0.14 mM NADH, and crude enzyme (final volume 3 m1). Increase in absorbance at 340 nm for 3-4 min at room temperature (25°C) was recorded. Absorbance (340 nm/min) was calculated from initial linear portion of the curve.

2.3.4. Glutamate Dehydrogenase (GDH)

Extraction buffer (pH 7.9) consisted of 0.05 M imidazole, 5 mM DTT. Leaves (1 g) were grinded using liquid N2 in the presence of cover slips in chilled mortar and pestle and were centrifuged at 12,000 xg for 40 min at 4°C. Supernatant was collected and stored at −20°C. The assays were carried out by continuous spectrophotometric rate determination method.

2.4. Crude Grain Protein Content and Nitrogen Use Efficiency Components

Nitrogen content in grains and straw was determined by micro-Kjeldhal method [18]. The nitrogen content of grain was then multiplied by the factor 6.25 to obtain crude grain protein content and expressed in g per 100 g of grain on a moisture free basis. The following nitrogen efficiency parameters were calculated for each treatment: nitrogen use efficiency, NUE (g g −1 ) as the ratio of grain yield to nitrogen supply, where N supply is the sum of soil NO3 − -N at planting, mineralized N and N fertilizer nitrogen utilization efficiency, NUtE (g g −1 ) as the ratio of grain yield to total plant nitrogen uptake nitrogen uptake efficiency, NUpE (g g −1 ) as the ratio of total plant N uptake to nitrogen supply.

2.5. Grain Weight per Plant

Random sample of the grains from individual genotypes was obtained. These grain samples were dried at room temperature (30°C) to minimize intrinsic moisture content uniformity. Then, these dried grain samples were weighed by electronic weighing balance to detect grain weight per plant.

2.6. Statistical Analysis

A complete factorial arrangement of treatments was used (soil condition × genotype) as a complete randomized design with three replications. Mean ± standard error mean (SEM) and critical difference at 5% (CD at 5%) values were calculated for statistical analysis. Correlation coefficients were also measured for various physiological and biochemical parameters.

3. Results and Discussion

There was variation in the heading dates within these finger millet genotypes, that is, the heading date for brown (PRM-1) genotype ranged from 77 to 85 days, whereas for golden (PRM-701) and white (PRM-801) genotypes ranged from 119 to 130 days. This indicates that brown (PRM-1) genotype is early flowering and golden (PRM-701) and white (PRM-801) are late flowering genotypes. Nitrogen fertilization significantly increased plant height and leaf area (Table 1), although there were found differences among the genotypes under different soil conditions. It was observed that, in brown genotype (Figure 1(a)), the SPAD value was higher in vegetative stage when the nitrogen was efficiently taken from the soil and then decreased in flowering and then after third dose of nitrogen there was increment in it. This means that brown genotype might be high nitrogen responsive, whereas, in golden (Figure 1(b)) and white genotypes, (Figure 1(c)), SPAD value was lower in vegetative stage and then increase in flowering, and, then, after third dose of nitrogen, there was decline in it. This means that golden and white genotypes are not able to take nitrogen immediately after addition of nitrogen, that is, they are low nitrogen responsive genotypes. The SPAD readings are calibrated to obtain the chlorophyll content of the leaves or correlated directly with plant performance [19–21], providing a practical method of assessing N status and N requirements. Successful use of chlorophyll meters varies with crop type and has been affected by many factors including varietal differences [22, 23], growth stages [24], nutrient deficiencies other than N [25], environmental conditions [19], and measurement positions on leaves [26]. 1000 grain weight was significantly highest (3.63 g) in white genotype (PRM-801) under low nitrogen condition, and lowest 1000 grain weight (2.09 g) was found in golden genotype under control condition. In the present study, increasing nitrogen rate improved yield attributes and grain yield. The positive effect of the, application of inorganic fertilizers on crop yields, and yield improvements have been reported earlier [27].


Assimilation of Food in Human Beings

In this article we will discuss about the Assimilation of Food in Human Beings.

Meaning of Assimilation of Food:

The absorbed food materials are transported by blood and lymph. Lymph is finally transferred to the blood circulation. The blood transports absorbed food materials to different body cells where food materials become integral component of the living protoplasm and are used for energy, growth and repair. This is called assimilation of food.

Assimilation of Proteins, Carbohydrates and Fats:

Amino acids are not stored but are taken up by the cells in connection with the synthesis of proteins. Proteins are used for growth, repair, etc.

Excess amino acids can be converted into glucose and then to fat and are thus stored. This is an irreversible reaction. Amino acids can also be converted to glucose and used as fuel for the cell. During their conversion to glucose the amino acids are deaminated (removal of amino groups NH2).

The liver is chief site for deamination, i.e., a process by which the amino group is removed from the amino acids resulting in the production of ammonia. The ammonia is soon converted into urea, which is filtered from the blood in the kidney.

The excess of the monosaccharide’s the glucose, fructose and galactose are usually stored in the liver and muscle cells in the form of glycogen (glycogenesis). Whenever, there is a deficiency of glucose in the blood the glycogen is converted into glucose (glycogenolysis).

Muscle glycogen is utilized during muscle contraction. Glucose is utilized in the production of energy for various body activities. A considerable amount of glucose is converted into fat and stored as such.

The fat is stored in the fat deposits of the body, such as subcutaneous layers, mesenteries, etc. The fat stored is a readily available source of fuel for the cells. Fat has important insulating properties in connection with the conservation of heat and maintenance of body temperature.

Fat also plays a protective role as filling or around packing material and between organs. In the liver phospholipids are formed which are returned to the blood to be used by all the cells. In the liver cells the fats are converted into amino acids and carbohy­drates. Vitamins, salts and water are also useful for various metabolic processes.

Egestion (= Defecation):

The elimination of faeces from the alimentary canal is called egestion or defecation. The faeces is waste matter discharged from the alimentary canal.

Mechanism of Egestion:

Peristalsis gradually pushes the indigestible materials of the small intestine into the large intestine or colon. Normally 1500 ml of chyme passes into the large intestine per day. The colon absorbs most of the water. It also absorbs electrolytes, including sodium and chloride from the chyme.

The epithelial cells of the colon also excrete certain salts such as iron and calcium from the blood. Escherichia coli (bacterium) lives in the colon which feeds on undigested matter. This bacterium, in turn, produces vitamin B12 (cobalamin), vitamin K, vitamin В1 (thiamine) and vitamin B2 (riboflavin) which are absorbed by the wall of colon. Consequently, the chyme converts into semisolid faeces.

As the pellets of faeces enter the rectum, distension of rectal wall induces the feeling of defecation due to a “defecation reflex”. This reflex initiates peristalsis in the last part of the colon (sigmoid colon) and the rectum, forcing the faeces towards anus. As the faeces reaches anus, involuntary relaxation of the internal anal sphincter and voluntary relaxation of external anal sphincter cause defecation.

Voluntary contractions of the diaphragm and abdominal muscles forces the sphincters open, and the faeces is expelled through the anus (contraction of the abdominal muscles and lowering of the diaphragm increases the intra-abdominal pressure which aids in the process of defecation). In infants, the defecation occurs by reflex action without the voluntary control of the external anal sphincter.

Constituents of Faeces:

The faeces consists of about three-fourth water and one- fourth solid matter. Of the solid matter is about 3 per cent bacteria, 10 to 20 per cent fat, 2 to 3 per cent protein, about 15 per cent inorganic matter and 30 per cent undigested roughage and dry constituents of digested juices.

Dead mucosal cells, mucus and cholesterol also occur in the faeces. Its brown colour is due to brown pigments, stercobilinogen and stercobilin, which are derivatives of bilirubin.

Balanced Diet:

A diet is said to be balanced when various nutritional materials i.e., proteins, carbohy­drates, fats, minerals, vitamins, roughage and water are present in sufficient amount and proper proportion.

Various constituents of the balanced diet provide energy, growth, repair, replacement of cells, and physiological regulation. Our food should contain the various nutrients in such proportions as can satisfy all the needs of m body.

It has been discovered that of our energy requirement, we obtain about 50% from carbohydrates, 35% from fats and 15% from proteins. Thus, we daily require about 400 to 500 grams of carbohydrates, 60 to 70 grams of fats and 65 to 75 grams of proteins. Balanced diet of each individual can be determined according to his or her needs.

Nutritional Requirements of Humans:

(i) Energy yielding nutrients:

Carbohydrates and lipids (fats) are chief energy giving nutrients. Proteins can also give energy.

(ii) Body building nutrients:

Proteins are chief body building nutrients.

(iii) Metabolic regulators:

E.g., vitamins, water and mineral salts.

(iv) Hereditary substances:

E.g., Nucleic acids (DNA and RNA).

Besides carbohydrates, proteins, fats, vitamins, minerals and water, roughage is also essential in diet.

Calorific Value of Carbohydrate, Protein and Fat:

Carbohydrates, proteins and fats serve as the chief sources of energy in humans. These are oxidized and transformed into ATP, the chemical energy form used by cells for their various activities.

Because heat is the ultimate form of all energy, the energy value of food (or any fuel) is expressed in terms of a measure of heat energy it produces on combustion. The heat energy released by combustion of one gram of food is usually known as its gross calorific value.

It is defined as the amount of heat produced in calories (cal) or in joules (J) from complete combustion of 1 gram food in a bomb calorimeter (a closed metal chamber filled with O2). The calorific value is usually expressed in terms of kcal per gram or kilojoules per gram.

(1kcal = 4.184kJ) One kilocalorie is the amount of heat energy needed to raise the temperature of one kilogram of water through 1°C (1.8°F). It is referred to kcal as the Calorie or to kJ as Joules (always capitalized). The calorific values of carbohydrates, proteins and fats are 4.1 kcal/g, 5.65 kcal/g and 9.45 kcal/g, respectively.

Physiologic Value of Carbohydrate, Protein and Fat:

The actual amount of energy liberated in the human body due to combustion of 1g of food is the physiologic value of food. It is always less than gross calorific value calculated by bomb calorimeter. The physiologic values of carbohydrates, proteins and fats are 4.0 kcal/g, 4.0 kcal/g and 9.0 kcal/g respectively.

The Physiologic Value:

The actual amount of energy liberated in the human body due to combustion of 1 g of food is the physiologic value of food. It is always less than gross calorific value calculated by bomb calorimeter. The physiologic values of carbohydrates, proteins and fats are 4.0 Kcal/g, 4.0 Kcal/g and 9.0 Kcal/g respectively.

Calorific Value and Physiologic Value of Carbohydrate, Protein and Fat:

1 Kilocalorie (Kcal) = 1000 calories

Vitamins:

N.I. Lunin (1881) discovered vitamins. Hopkins and Funk (1912) pro-founded a ‘Vi­tamin Theory’. Vitamin was chemically an amine and was vital to life. Hence Funk (1911) named it Vitamine (L. vita – life + amine = vital amine). The term ‘vitamin’ is retained now omitting the terminal ‘e’ in its spelling. The book entitled ‘The vitamins’ was written by Funk and published in 1922.

Vitamins are regarded as organic compounds required in the diet in small amounts to perform specific biological normal maintenance of optimum growth and health of the organisms.

Vitamin С is the most sensitive of all vitamins to heat. Antineuritic vitamins are B1, B6 and B12. Antioxidant vitamins are A, E and C.

Vitamins are divided into two main groups.

Fat soluble vitamins, e.g., vitamins A, D, E and К

Water soluble vitamins, e.g., vitamins В-complex, С and P.

Minerals:

Minerals are classified as major and trace. This classification is based on how much of the mineral is needed to the body. Major minerals (macro minerals) are important nutrients in our diet. It is suggested that we consume 0.1 gm of each of these minerals per day. Trace minerals (micro minerals), as their name indicates, are needed in only small amounts. It is suggested that we consume 0.01 gm of each trace mineral per day.


It is a great pleasure for me to invite you to submit a manuscript to the Special Issue "Organic&ndashInorganic Hybrid Nanomaterials", which will be published in the journal Nanomaterials.

This Special Issue targets interdisciplinary state-of-the-art research articles, communications, and reviews. Two rapidly developing vectors are currently emerging in hybrid systems studies: stable and transient hybrid systems. Combining individual contributions from these areas will allow us to produce a most impactful journal issue:

Hybrid nanomaterials that contain organic components (organic groups or molecules, ligands, biomolecules, pharmaceutical substances, polymers, etc.) and inorganic components (metal ions, metal clusters or particles, salts, oxides, sulfides, non-metallic elements and their derivatives, etc.) play a paramount role in contemporary research. Advanced molecular architectures based on hybrid nanomaterials admittedly provide an outstanding driving force for the active progress in several research areas, including the development of new platforms for drug delivery, smart and stimuli-responsive materials, sensors, as well as nanomedicine, industrial technologies, material sciences, and energy applications.

2) Transient hybrid systems

Linking organic molecules to metal nanoparticles may create highly reactive hybrid organic&ndashinorganic systems. Despite the short lifetime of such nanostructures, they ensure facile chemical activation of organic molecules. Their key applications arise in the fields of catalysis and organic synthesis, where nanomaterials are currently promoting a new wave of highly active and selective catalyst development. Top-notch scientific reports on nanoparticle catalysis, dynamic catalysis or &ldquoсocktail-type&rdquo catalysis are highly welcomed and definitely fall within the scope of this Special Issue.

Thus, submissions regarding Stable hybrid systems or Transient hybrid systems are cordially invited.

Please note that Nanomaterials is an open access journal, and the whole Special Issue will be freely available for all readers across the world. Information about open access options and conditions is provided at the journal website.

Prof. Dr. Valentine P. Ananikov
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Nanomaterials is an international peer-reviewed open access monthly journal published by MDPI.

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