Regulation of growth and some key physiological and biochemical attributes in salt stressed plants of rice (Oryza sativa L.) by exogenous application of nitric oxide

Abstract

Keeping in view the newly discovered role of nitric oxide in plant growth, development and salt tolerance, an initial experiment was carried out for optimization of nitric oxide concentrations, which were most effective in improving the seed germination rate and early seedlings growth in rice under saline stress. Pre-sowing seed treatment with varying levels (0.05, 0.1, 0.2, 0.3, 0.4, 0.5 mM) of nitric oxide was applied to seeds of four rice cultivars (Shaheen Basmati, Basmati PB-95, KS-282 and IRRI-6), which were subjected to two levels (0 and 80 mM) of salt stress. Salt stress markedly inhibited the seed germination attributes and early seedlings growth in all four rice cultivars. Of all nitric oxide levels 0.5 mM was slightly effective, however, 0.1 and 0.2 mM were most effective in improving seed germination attributes and early seedlings growth of salt stressed rice plants. The both levels (0.1 and 0.2 mM), which were found relatively more effective in first experiment, were used in the yield experiment to study the regulatory role of nitric oxide on various growth, physiological and biochemical attributes of salt stressed rice plants. In this experiment both pre-sowing seed treatment and foliar spray modes were adopted for exogenous addition of nitric oxide to salt stressed rice plants. Salt stress caused a marked suppression growth, chlorophyll content, gas exchange attributes, chlorophyll fluorescence, uptake of essential nutrients, total phenolics and yield content while increased tissue Na+ and Cl- , proline, ascorbic acid, MDA, H2O2 and the activity of antioxidant enzymes including CAT, POD and SOD in all four rice cultivars. Of both nitric oxide levels, 0.1 mM was relatively more effective in improving growth and physiological attributes of salt stressed rice plants as compared to 0.2 mM. Of all four rice cultivars, Shaheen Basmati and IRRI-6 performed better for chlorophyll content, gas exchange attributes and activity of enzymatic antioxidants (SOD, POD and CAT), while KS-282 and IRRI-6 performed better for, total phenolics and yield content. Overall, exogenous nitric oxide treatment was effective in improving fresh and dry biomasses (in both shoots and roots), chlorophyll content, photosynthetic rate, water relation attributes, K+/Na+ ratio, Ca2+ content, activity of enzymatic and non-enzymatic antioxidants and proline content, while in decreasing Na+ and Cl- ions, MDA and H2O2 content.