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The development of drought tolerant genotypes for peanuts has now become a priority due to the growing number of drought-prone areas. The effects of drought stress on nitrogen metabolism was studied in leaves of two groundnut cultivars with differential sensitivity to drought stress, K-134 (drought tolerant) and JL-24 (drought sensitive) subjected to different regimes of water stress conditions for a duration of 12 days. The total protein content in leaves of both cultivars declined with progressive accumulation of free amino acid levels. Concurrently, the protease activity in the tissues was also increased. Ammonia content was increased in both cultivars and comparatively higher ammonia levels were recorded for cv. JL-24. A gradual increase in the activities of key enzymes involved in nitrogen metabolism such as glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (NADH-GDH and NADPH-GDH), aspartate aminotransferase (AAT) and alanine aminotransferase (ALAT) was observed in both cultivars subjected to water stress. The increase in enzyme activities was more pronounced in the drought tolerant than in the drought sensitive cultivar. Contrarily, the activities of nitrate reductase (NR) and nitrite reductase (NiR) were decreased in the stressed plants. The extent of decrease was more in cv. K134 than cv. JL-24. The results indicate that drought tolerance of cultivar K-134 may be attributed at least in part to the ability to shift the metabolic rate leading to a greater accumulation of amino acids coupled with lower levels of ammonia and largely by reassimilation as evidenced by relatively greater activities of GS and GOGAT in the tissue. The physiological importance of enzyme alterations under water stress was investigated in relation to plant metabolism.

The present study was carried out to study the variation of antioxidative potentials in terms of activities of antioxidative enzymes along with the accumulation of osmolytes and plant growth in the leaves of two groundnut (Arachis hypogaea L.) cultivars namely K-134 and JL-24 under three levels of water supply conditions. Growth retardation in terms of root and shoot length, and in relation to the severity of drought stress was more pronounced in susceptible cv. JL-24 than in in tolerant cv. K-134.The leaves of cv. JL-24 showed greater reduction in dry weight and relative water content (RWC) when compared to cv. K-134 with increasing stress intensity. The activities of antioxidative enzymes which include superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), glutathione reductase (GR) and osmolytes such as proline and glycinebetaine were significantly high in the water-stressed leaves of both cultivars and the magnitude of increase was dependent on the severity of stress. These results highlight the ability of groundnut cultivars to up-regulate the enzymatic antioxidant system and osmolytes to withstand oxidative during water deficit conditions. However, the extent of up-regulation varied between the cultivars K-134 and JL-24, leading to the higher amounts of antioxidants and osmolytes in cv.K-134, supporting its drought tolerance. Furthermore, the drought tolerant nature of cultivar K-134 was well supported by lower rates of membrane lipid peroxidation, electrolytic leakage and chlorophyll breakdown.

Drought tolerance represents a growing threat to crop productivity. Safflower is one of the major oilseed crop enriched with various nourishing elements. In order to unravel the drought responses and recovery, a changes in cell components and specific isoforms of antioxidative enzymes in safflower (Carthamus tinctorius L. cultivar A1). Water stress (0.0%, 75%, 50% and 25% of soil moisture levels) was induced to safflower plants after 21 days of vegetative growth. After 8 days of stress imposition, plants were harvested and analysed for various parameters. A drastic decrease in the relative water content was observed during the stress and resumed the normal level after recovery. The extent of membrane damage was high under higher stress levels. These plants also showed increased levels of lipid peroxidation as evidenced from the increased malondialdehyde content, coupled with the increase in activities of antioxidant enzymes and their isoforms whereas the values in stress-recovered plants observed to be near to their respective controls. On activity gels, 12 distinct isoforms of SOD were detected; among these 10, 11 and 12 isoforms were specific under moderate and severe water stresses. Three isoforms of CAT were identified of which 2 were specific under severe water stress. In the case of POD, isoforms 2, 4, 6 and 7 were common for moderate and severe stresses whereas, POD 3 and 5 were observed only under severe stress and POD1 remained as unchanged. On recovery, the cell components and specific isoforms of antioxidative enzyme levels appeared to be that of the normal controls could be considered and used as selection criteria for improving safflower drought tolerance.