Induction of heat stress tolerance in barley seedlings by pre-sowing seed treatment with glycinebetaine

Heat stress adversely affects plant growth and development, while glycinebetaine ( GB) plays a protective role under stressful conditions. The objective of this study was to assess the optimum level of GB for use as a presowing seed treatment and the subsequent effect on the heat tolerance of barley ( Hordeum vulgare L. cv. Haider-93) seedlings. Among a range of GB levels, the 20 mM concentration emerged as the most effective in enhancing seed germination, shoot fresh and dry weight and shoot water content under heat stress, and this level was selected for further studies. Time course changes revealed that the seedlings developing from 20 mM GB treated seeds had greater shoot dry weight, net photosynthetic rate (P-N), leaf water potential (psi(w)) and reduced relative membrane permeability (RMP), compared to no-GB treated plants under heat stress. Correlations between dry weight and high P-N (r = 0.881), low psi(w) (r = - 0.938) and RMP ( r = - 0.860) of shoots suggested the involvement of GB in heat stress tolerance. Leakage of Ca2+ and NO3- was the greatest followed by K+ and PO43- under no-GB seed treatment, and GB application under heat stress appreciably reduced the leakage of all these ions, particularly Ca2+, K+ and NO3-. In conclusion GB absorbed by seeds, after translocation to the seedlings, enhanced their capacity to maintain greater water content, and higher seedling vigor by virtue of increased P-N, reduced RMP and leakage of important ions under heat stress. These results have implications for final field stand under the conditions where the ambient temperature is supra-optimal for barley growth.