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.
