Y. P. Abrol

Photosynthesis and Nitrogen-Use Efficiency

In C3 crop plants about 60–80% of leaf nitrogen (N) is invested in the photosynthetic apparatus, and N nutrition plays a crucial role in determining photosynthetic capacity. The proportion of leaf N invested in photosynthetic components is fairly constant. By contrast, both N per unit leaf area and the allocation of N between the component photosynthetic processes depend on environmental factors such as N availability, irradiance and CO2 concentration. Light-harvesting and electron transport components often show a co-ordinated and equivalent response to N nutrition. In contrast, most studies have shown disproportionately large changes in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in response to N supply, demonstrating the importance of this protein in leaf N economy. At low light, for a given N availability, more protein is allocated towards light harvesting components in order to maximize light capture and, expressed per unit Chl, electron transport and carboxylation capacities are relatively small. High irradiance tends to alter the partitioning of N away from thylakoid protein to soluble proteins, particularly Rubisco. Growth at elevated CO2 often leads to decreases in the amounts of Rubisco and other photosynthetic components on a leaf area basis. This is explicable in terms of greater N sinks elsewhere in the plant as a result of increased carbohydrate availability and acclimatory changes. Models predict that in order to arrive at optimal N use efficiency (NUE) at likely future ambient CO2 concentrations, leaves will need to achieve a redistribution of N so that the ratio between the capacities for regeneration of ribulose-1,5-bisphosphate and carboxylation increases by 30–40%. Human intervention to improve the NUE of crops would have economic and environmental benefits, reducing pollution of water supply by nitrates. The NUE of photosynthesis could be increased either through manipulation of Rubisco amounts or properties, or by decreasing photorespiration. While decreasing Rubisco content could enhance NUE by only about 5%, eliminating photorespiration could produce a change of more than 50%.

Effect of split application of sulphur and nitrogen on growth and yield attributes of Brassica genotypes differing in time of flowering

According to prevalent agronomic practices for cultivation of Brassica genotypes, N is applied in split doses, while S is applied as a basal dose. This may create imbalance in the supply of these nutrients during the growth and development of the crop because metabolism of N and that of S are closely linked and play a central role in protein synthesis. The requirement of one depends on the supply of the other, and the imbalance in their supply causes a reduction in the yield because of reduced uptake and assimilation of the two nutrients. In the present investigation, therefore, S was applied in split doses, along with N, to study its effect on growth and yield attributes of Brassica juncea (L.) Czern. and Coss. (V1) and Brassica campestris L. (V2). In the experiment, conducted in the field, 40 kg S ha−1 as CaSO4 (gypsum) was applied either in a single basal application (S1) or in two (S2) or three (S3) split applications; and 100 kg N ha−1 as urea was applied either in two (N2) or three (N3) splits. Biom...

Nitrate reductase activity in developing wheat ears

Die Fruchtstände der Weizenpflanzen reduzieren während ihrer Entwicklung beachtliche Mengen von Nitratstickstoff.

Potential for nitrate reduction in wheat (triticum aestivum L.)

Abstract Following the prevalent agronomic practice of applying N fertilizer in two splits at optimum levels recommended for maximum yield viz. 120 kg N ha, to two wheat (Triticum aestlvum L.) cultivars, which differ in in vivo nitrate reductase (NR) activity, it was observed that the activity is high in the first formed leaf blades and declines in the successively formed ones. Enhancement in the activity subsequent to incubation of excised leaf blades in NO3 ‐ suggests that the substrate (NO‐ 3) is limiting and that the leaf blades, particularly the upper ones, have the potential to reduce additional amounts of NO3 ‐. High NR cultivar has greater potential than the low NR cultivar. The studies suggest that it may be possible to increase the NO3 ‐ moles reduced and thus enhance the reduced N content in case the nitrogen is available at later stages of growth.

Nutritional potential ofVigna minima (Roxb.) Ohwi and Ohashi

The seed protein content and amino acid composition of 14 natural populations and their three-generation progenies (grown in different locations) belonging toVigna minima (Roxb.) Ohwi & Ohashi and ofV. umbellata cv IC 1568 have been investigated. The populations ofV. minima were sampled from different ecozones of Western Ghats of Kerala and Tamil Nadu (India). The range of variation in protein levels is narrow, but the protein content of the coastal population is higher than the rice bean suggesting its breeding potential for high protein and salt tolerant lines of rice bean. Although the seed protein content shows genotype × environment interaction, there is a substantial genetic variability among the populations. The tenuous relationship between protein content and yield conponents suggest the presence of correlation breakers which can be utilized in breeding programmes of rice bean. There is a broad genetic base in the levels of essential amino acids, and the range of variation observed is higher than that recorded for different species ofVigna andPhaseolus. The wild relative is nutritionally as good as or superior to the cultigen.

Effect of photorespiratory metabolites, inhibitors and methionine sulphoximine on the accumulation of ammonia in the leaves of mung bean and Amaranthus

Abstract The free ammonia (NH3) level, and its accumulation in the presence of methionine sulphoximine (MSO) were investigated in the leaves of a C3 (Vigna radiata) and a C4 (Amaranthus edulis) plant, both in the presence and absence of photorespiratory inhibitors, isonicotinyl hydrazide (INH) or α-hydroxypyridine methane sulphonate (α-HPMS) as well as when fed with photorespiratory intermediates, glycolate or glycine. The endogenous level of free NH3 was slightly greater in the C4 than in the C3 plant in control treatments but when NH3 assimilation was blocked with MSO, the difference was reversed. The inhibition of MSO-induced accumulation of NH3 by INH and α-HPMS was four times more effective in Vigna (C3) than in Amaranthus (C4). Glycine feeding enhanced the NH3 accumulation with MSO and the enhancement was similar in both C3 and C4 plants. However, NH3 accumulation with MSO and glycolate feeding was more in the C3 than in the C4 plant. The increase in MSO-induced NH3 accumulation on glycine or glycolate feeding were inhibited ny INH or α-HPMS, respectively.

Photosynthetic Characteristics in Two Wheat Genotypes as Affected by Nitrogen Nutrition

Chlorophyll (Chl) a and b content, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) content and activity, and electron transport rate were measured in flag leaves of wheat genotypes Uniculm and Kalyansona, grown at suboptimal and optimal supply of nitrogen. The Chl content, RuBPCO activity, and electron transport rate were decreased due to suboptimal nitrogen supply only in Kalyansona. There was no change in the ratio of RuBPCO and photosystem 2 (PS2) activity at various stages which suggests that there was no alteration in distribution of N due to additional N supply.

Carbon dioxide assimilation in urea-treated wheat leaves

Abstract Application of 10 mM urea to the flag leaf of wheat plants enhanced in vivo urease activity several fold. Photosynthetic rate was also increased considerably. There were significant differences in the leaf internal carbon dioxide (CO2) concentrations between the urea‐treated and untreated leaves. The finding that carbon (14C) was detected in the ethanol extract of the leaves fed with 14C‐urea suggests that CO2 released from urea is re‐fixed by the leaves.

Nutritional potential of Vigna minima (Roxb.) Ohwi and Ohashi : II. Seed protein fractions and their amino acid composition

Quantitative variation in different fractions of seed proteins and their amino acid levels in populations ofVigna minima (Roxb.) Ohwi and Ohashi and inV. umbellata cv. IC 1568 — the rice bean — were investigated. Globulin I fraction, together with globulin II, constitutes 38 to 54 per cent of the total seed protein. The alkali soluble (glutelin) fraction is the second largest fraction. Both these fractions show broad range of variation, suggesting a broad genetic base. The profiles are population specific; the coastal population, which contains higher seed protein also possesses maximum levels of globulin I and glutelin fraction suggesting its potentiality for breeding lines with high protein content, high nutritive value, and salt tolerance. Protein content is positively correlated with globulin I and glutelin fractions, which are in turn positively correlated with each other. The amino acid profiles are specific not only to the fractions but also to the populations. The range of variation in the levels of all amino acids in different fractions is broad suggesting substantial genetic diversity. The average levels of lysine and sulphur amino acids are high in globulin I and glutelin fractions.Comparaison des variations quantitatives et qualitatives des differentes fractions obtenues a partir des graines de Vigna minima et V. umbellata

Effect of exogenous supply of amino acids, amide, urea and ureide on free NH4+ level in mung beans

The results of experiments on the possible source(s) of ammonia for the mung bean are reported. Different nitrogenous metabolites were fed to primary leaves of mung bean seedlings with and without methionine sulphoximine (MSO), an inhibitor of glutamine synthetase (GS). Their role in foliar ammonia loss is discussed.