BIOCHEMICAL ASPECTS OF DROUGHT TOLERANCE INDUCED BY SEED PRIMING IN WHEAT

Abstract

Water stress is the major abiotic factor that limits crop productivity. Among various strategies, seed priming is low cost, easy low risk approach to improve the abiotic stress tolerance in crop plants. The effects of seed priming with varying concentrations of chitosan (0.1, 0.25 and 0.50 %), sodium nitroprusside (SNP) (75, 100 and 125μM) and sodium silicate (20, 40 and 60mM) on physiological and biochemical attributes in seeds, seedlings and wheat plants under non-stress, osmotic stress by poly ethylene glycol (PEG) and drought were appraised in this study. Seed priming with chitosan, SNP and sodium silicate promoted the activities of proteases, soluble proteins, hydrolases, α- amylase, α- naphthyl acetate esterase activities in the seeds. Moreover, tested seed priming treatments induced enhancement in antioxidant enzymes. Hydropriming induced modulations in seed biochemical processes were generally different and less prominent as observed by other tested priming treatments. In general, tested seed priming treatments brings out the production or activation of enzymes in the seeds that are required for the degradation and mobilization of seeds reserves and defense response. In seed germination experiments, osmotic stress induced by 15 % PEG-6000 adversely affected the seed germination attributes while chitosan SNP and sodium silicate seed priming improved the germination (FGM, GE, VI, GR, MGT and GI) and promoted the early seedling growth under non-stress and osmotic stress conditions. In seedling experiments, chitosan, SNP and sodium silicate priming generally resulted in promotion of early seedling establishment and synchronized growth along with better biochemical and physiological attributes. Osmotic stress increased the peroxidase, protease, α-amylase activities, total soluble proteins, malondialdehyde (MDA) contents, reducing and total sugars while dropped the relative water content in the leaves. Chitosan seed priming improved the osmotic stress tolerance of seedlings evident from adjusted antioxidants activities (POD, CAT, SOD) soluble sugars, improved CMS and leaf RWC and reduced lipid peroxidation. Similarly, SNP priming significantly improved the CMS, RWC, TPC, proteins and reducing sugars while reduced the hydrolases (protease, α- amylase) activities and lipid peroxidation in seedlings providing evidence for lesser osmotic stress induced injury and improvement in stress tolerance. Moreover, sodium silicate (60mM) priming enhanced the POD, TPC, CMS, RWC and reducing sugars while decreased the CAT, protease, α-amylase and SOD activities and MDA content in leaves under osmotic stress indicating improvement in stress tolerance. In pot experiments, drought stress adversely affected the biochemical, physiological processes, and yield in wheat plants grown from non-primed seeds. In wheat plants grown from seeds primed with chitosan, SNP or sodium silicate antioxidants (CAT, POD, SOD and TPC), osmoprotectants (GB, proline and sugars), CMS, leaf water relations (WP, OP, TP and RWC) and pigments generally improved while hydrolyzing enzymes and lipid peroxidation decreased under drought stress. Chitosan SNP and sodium silicate priming improved the grain yield, 100 grain weight and plant biomass grown under drought stress. In conclusion, tested seed priming treatments successfully improved the seed germination and performance and alleviated the adverse effects of osmotic and drought stress in wheat seedling and plants respectively.