Chemo-priming with Mannose, Mannitol and H2O2 Mitigate Drought Stress in Wheat

Drought is a worldwide problem, getting more serious with global climate change. Among various strategies, seed priming is the simplest approach for improving drought tolerance in crop plants. Seed priming treatments were applied by soaking seeds in aerated solution of 1% mannose (56 mM) and 10 mM mannitol for 8 h while 100 mu M H2O2 for 5 h. Seeds soaked in aerated water (hydropriming) and non-primed seed were used as controls. Drought stress significantly reduced the seedling fresh weight and leaf relative water content. Pre-sowing seed treatment with mannitol significantly increased the seedling, root and shoot fresh as well as dry weights under non-stress condition. Moreover, H2O2 increased the root length; seedling and root dry weights while mannose increased the shoot dry weight under drought stress. Leaf relative water content (RWC) improved after mannitol and H2O2 priming under drought and non-stressed conditions. Hydropriming increased the root and shoot fresh weights, shoot dry weight and RWC under non-stress condition while seedling, root, shoot fresh weights and shoot dry weight along with raised TSP, MDA, reducing sugars under drought stress. Drought stress raised the total soluble protein (TSP), protease, APX and POD activities, MDA and reducing sugars in leaves. Mannitol and H2O2 confiscate the drought-induced increase in TSP while H2O2 significantly increase it under non-stress condition. Drought stress reduced the catalase activity in leaves while H2O2 and mannitol priming brought it back to control level. Drought stress elevated the MDA in leaves and H2O2 treatment prevented this increase. Only mannose priming rose the reducing sugars in leaves under non-stress condition. Under drought, mannose and mannitol priming raised the reducing sugars in the leaves as a tactic for osmotic adjustment. In conclusion, seed priming treatments ameliorated the drought tolerance in wheat by elevating the level of antioxidants, reducing oxidative damage of biomolecules and accumulating more reducing sugars for osmotic adjustments.