Ishrat Khan

Modulation of antioxidant defence system for arsenic detoxification in Indian mustard.

This study investigates the modulation of antioxidant defence system of Indian mustard (cv. Pusa Jai Kisan) against the arsenic (As)-induced toxicity in 20-day-old plants, exposed to 5 and 25 microM As for 96 h in hydroponic culture. Reduction in plant growth, measured in terms of root and shoot dry weights, was insignificant with 5 microM, but highly significant with 25 microM As treatment. Shoots accumulated more As than roots. The extent of oxidative stress in the leaves was measured as the rate of lipid peroxidation. The As treatments significantly increased the activities of antioxidative enzymes (superoxide dismutase, ascorbate peroxidase and glutathione reductase) and the contents of antioxidants metabolites (glutathione and ascorbate), the increase being dependent on exposure time. Increase in the activity of catalase was not significant, however. In conclusion, Indian mustard was able to detoxify the low As level through induction of antioxidant defence mechanism.

Identification and Comparative Analysis of MicroRNAs Associated with Low-N Tolerance in Rice Genotypes

Background Nitrogen [N] is a critical limiting nutrient for plants and has to be exogenously supplied to many crops, to achieve high yield with significant economic and environmental costs, specifically for rice. Development of low-input nitrogen sustainable crop is necessary for sustainable agriculture. Identification of regulatory elements associated with low-N tolerance is imperative for formulating innovative approaches for developing low-N tolerant crop plants, using gene manipulation. MicroRNAs (miRNAs) are known to play crucial roles in the modulation of gene expression in plants under various environmental conditions. Methodology/Principal Findings MiRNAs associated with low-N tolerance have not been identified so far. In this study, we investigated microarray-based miRNA expression in low-N tolerant and low-N sensitive rice genotypes under low N condition. Expressions of 32 miRNAs differed significantly in the two genotypes. Of these 32 miRNAs, expressions of nine miRNAs were further validated experimentally in leaves as well as in roots. Of these differentially expressed miRNAs, six miRNAs (miR156, miR164, miR528, miR820, miR821 and miR1318) were reported in leaves and four (miR164, miR167, miR168 and miR528) in roots. Target genes of all the 32 miRNAs were predicted, which encode transcription factors, and proteins associated with metabolic processes or stress responses. Expression levels of some of the corresponding miRNA targets were analysed and found to be significantly higher in low N-tolerant genotype than low-N sensitive genotype. These findings suggested that miRNAs played an important role in low-N tolerance in rice. Conclusions/Significance Genome-wide differences in expression of miRNA in low N-tolerant and low N-sensitive rice genotypes were reported. This provides a platform for selection as well as manipulation of genotypes for better N utilization efficiency.

Effect of Timing of Sulfur Fertilizer Application on Growth and Yield of Rapeseed

Abstract There is usually a positive yield response when sulfur (S) is applied to rapeseed (Brassica rapa L.) plants grown on S-deficient soils. Recommendations include application of some of or the entire amount of S at planting, but the plant requirement as well as availability of S to rapeseed during its various phenological stages is not well documented. In a field trial, 40 kg S ha−1 was applied as gypsum (CaSO4·2H2O) at planting (T1), during vegetative (T2, 30 days after sowing), flowering (T3, 50 days after sowing), and pod-filling (T4, 65 days after sowing) stages, and in split doses (T5). Biomass accumulation, leaf-area index, and leaf photosynthetic rate were studied at various growth stages. Seed S (sulfate and organic S) and yield parameters were studied at harvest. Sulfur (40 kg S ha− 1) applied in three split doses during different growth stages caused maximum increase in these parameters, followed by T2 and T1. However, no significant discernable difference was observed for the application at planting (T1) and during vegetative stage (T2). No significant response was seen following the application of T3 and T4 when compared with the control (T0). On the basis of these results, we concluded that application of S fertilizer in split doses during growth stages is better than application of the entire amount of S at any stage for obtaining optimum yield of rapeseed.

Sulphur Interaction with Other Nutrients

Sulphur is known to interact with almost all essential macronutrients, secondary nutrients and micronutrients. These interactions can either enhance or reduce growth and yield of crops by influencing the nutrient uptake and utilization. Better understanding of these relationships can lead to more efficient crop production, higher yields, improved crop quality and harvestibility. Future improvements in crop varieties, water utilization, and general improvements of cultural techniques will require a better understanding of nutrient interaction. This chapter focuses the interaction of sulphur with other nutrients.

Effect of sulfur fertilisation on oil accumulation, acetyl-CoA concentration, and acetyl-CoA carboxylase activity in the developing seeds of rapeseed (Brassica campestris L.)

The effect of sulfur (S) fertilisation on oil accumulation, acetyl-CoA concentration, and activity of acetyl- CoA carboxylase (EC 6.4.1.2) was determined in the developing seeds of rapeseed (Brassica campestris L. cv. Pusa Gold) grown in the field with and without S. The period between 14 and 35 days after flowering (DAF) was identi- fied as the active period of oil accumulation in the developing seeds of rapeseed. The accumulation of oil was pre- ceded by a marked rise in acetyl-CoA carboxylase activity and acetyl-CoA concentration, which declined rapidly when oil accumulation reached a plateau. Starch and soluble sugar content decreased, while protein content increased during the period of active oil accumulation in the developing seeds (i.e. 14-35 DAF). Sulfur fertilisation signifi- cantly (P < 0.05) enhanced the oil accumulation in the developing seeds at all the growth stages except at 7 DAF. The increase in the oil content was 13.0-52.0% with S fertilisation over the control treatment. Sulfur fertilisation also increased acetyl-CoA concentration, acetyl-CoA carboxylase activity, and soluble protein, sugar, and starch content in the developing seeds. It is suggested that the increase in the oil content with S fertilisation may be associated with increases in acetyl-CoA carboxylase activity through the enhancement of acetyl-CoA concentration. Further, the increased sugar content due to S fertilisation provided enough carbon sources for oil biosynthesis.

Differential response of wheat genotypes to applied nitrogen: biochemical and molecular analysis

Nitrogen-efficient and nitrogen-inefficient wheat genotypes were identified on the basis of the differential response of 16 wheat genotypes with low (1 mM) and high (25 mM) nitrogen (N) supply. Growth performance, measured in terms of fresh weight, dry weight and length of root and shoot, was higher in N-efficient than N-inefficient wheat genotypes at low N levels. Interestingly, although the growth of N-efficient genotypes did not show any change with increasing level of N supply, there was a marked increase in the growth of N-inefficient genotypes with the increase in N level. To work out the basis of this differential response of wheat genotypes to low N levels, we investigated the nitrate uptake rate of root and activities of nitrate assimilatory enzymes in the leaves of N-efficient and N-inefficient wheat genotypes. Nitrate uptake kinetics of these genotypes revealed that the uptake of nitrate in N-efficient genotypes was mediated by high-affinity nitrate transporter systems, whereas those of N-inefficient genotypes was mediated by low-affinity nitrate transporter systems. Study of the activities and expression levels of nitrate assimilatory enzymes in N-efficient and N-inefficient wheat genotypes showed that nitrate reductase (NR) and glutamine synthetase (GS) play important roles in N assimilation under low-nitrogen conditions.

Effect of S and N nutrition on N-accumulation and N-harvest in rapeseed-niustard (Brassica juncea L. and Brassica campestris L.)

The effect of S and N application on N-accumulation and N-harvest in rapeseed mustard (Brassica juncea L., V1; and Brassica campestris L., V2) was studied under field conditions with a randomized block design. Three treatments viz. 0S+100N (T1), 40S+100N (T2) and 60S+150N (T3) were applied. The results showed that application of S along with N increased N-accumulation in both genotypes at all growth stages compared with N applied alone. This increase in N-accumulation was due to an increase in nitrate assimilation from reduced nitrogen forms as evidenced by the higher nitrate reductase (NR) activity in the leaves of plants grown with both S and N. This showed that application of S along with N considerably reduced the nitrate content in the leaves due to higher NR activity. The decline in nitrate assimilation was followed by an overall increase in N-accumulation in plants. Consequently, N content in the plant was increased from 22.1- to 146.2% and from 25.5 to −249.5% in V1 and V2 respectively, with the application of S along with N, compared with the application of N alone. N-harvest index was also higher in plants grown with both S and N compared with N alone. It is concluded that application of S along with N increases the accumulation of N. The treatment, T2 resulted in maximum improvement in these parameters.

Chromium Toxicity and Tolerance in Crop Plants

Heavy metals (HM) constitute a group of pollutants that exert a major influence on the integrity of soil, water and air. Chromium (Cr) is one of these pollutants and its amount has shown a multifold increase in the present era. The role of Cr in plants stands undefined. A non-essential element as it is, chromium exerts phytotoxicity by impairing growth and development, nutrient cycling and various metabolic processes. Plants exert a wide array of defense against the accumulated chromium. The present chapter describes the mechanism of phytotoxicity and phytotolerance under chromium stress.

Relationship between soil nitrate content and activities of NADH: and NAD(P)H :nitrate reductases in Indian mustard

The pattern of NADH- and NAD(P)H-specific nitrate reductase (NRs) activities in Indian mustard (Brassica juncea L. Czern. and Coss.) was monitored throughout growth stages. NAD(P)H:NR (EC 1.6.6.2) activity was maximum at early stages of growth (30 days after sowing, DAS), then declined gradually reaching to almost zero at 90 DAS. Contrary to this, NADH:NR (EC 1.6.6.1) activity was low at 30 DAS, then gradually increased till 90 DAS and thereafter, it became constant. The decrease in NAD(P)H:NR activity and increase in the NADH:NR activity were associated with the seasonal decrease in nitrate content in the soil.

Lipid biosynthesis in rapeseed as influenced by sulphur nutrition

The aim of this research was to study the effect of sulphur (S) nutrition on lipid biosynthesis and its related variables at various stages of seed development, and to find possible explanations for increased lipid content in the seeds of rapeseed due to S nutrition. Acetyl CoA carboxylase activity and contents of lipid, acetyl CoA, soluble sugar and starch were determined in the developing seeds of rapeseed (Brassica campestris L. cv. Pusa Gold) grown in the field with sulphur (+S) and without sulphur (−S). The period between 14–35 days after flowering (DAF) was identified as the active period of lipid accumulation in the developing seeds of rapeseed. The accumulation of lipid was preceded by a marked rise in acetyl-CoA carboxylase activity and acetyl-CoA content, which declined rapidly when lipid accumulation reached a plateau. Starch and soluble sugar content decreased during the period of active lipid accumulation in the developing seeds (i.e. between 14–35 DAF). Sulphur nutrition significantly (p<0.05) enhanced the lipid accumulation in the developing seeds in all the growth stages except at 7 DAF. Acetyl-CoA carboxylase activity and contents of acetyl CoA, sugar and starch were significantly (p<0.05) higher in the developing seeds of +S treated plants compared to −S treated plants. It is suggested that the increase in the lipid content with sulphur nutrition may be associated with the increases in acetyl-CoA carboxylase activity through the enhancement in the acetyl-CoA content. Furthermore, the increased sugar content due to S nutrition provided sufficient carbon sources.