Comparative study on nitrogen metabolism in a drought tolerant and a sensitive cultivar of groundnut (Arachis hypogaea L.) under drought stress

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.