Metabolic and Physiological Changes Induced by Nitric Oxide and Its Impact on Drought Tolerance in Soybean.

Nitric oxide (NO) is an important signaling molecule that plays a pivotal role in stress tolerance. To study the role of NO in drought tolerance and elucidate the underlying mechanisms, NO (0 and 100 μM) was applied to drought-treated soybean plants. Drought stress was imposed by PEG (5% (W/V) of PEG 6000. Nitric oxide improved growth of soybean plants under drought as evidenced by enhanced dry weight (30%). Nitric oxide caused a remarkable increase in activities of catalase and superoxide dismutase (SOD) and SOD expression (14.8-fold), which led to a significant decline in malondealdehyde content under drought conditions. Nitric oxide induced proline biosynthesis due to enhancing pyrroline-5- carboxylate synthetase (P5CS) expression (43.66-fold). The growth-promoting effect of NO application in soybean plants was concomitant with change in metabolic profile (phenolic acid and flavonoid compounds). Nitric oxide up-regulated of phenylalanine ammonia-lyase (PAL) expression in drought-treated plants and may influence on the phenylpropanoid production. Nitric oxide increased salicylic acid (SA) content in soybean plants under stress. So, NO and SA are jointly responsible for boosted tolerance to drought stress in soybean plants. The decrease in unsaturated fatty acid through NO application might reflect a reduction in oxidative damage. These results propose a multifaceted contribution of NO through regulation of physiological and metabolic processes in response to drought stress. [ABSTRACT FROM AUTHOR]