Effect of polyamines on thermotolerance and membrane stability of soybean seedling

The role of polyamines in the heat-shock protection of soybean seedling by application of exogenous polyamines (putrescine, spermidine and spermine) and their biosynthetic inhibitors involving CHA (cyclohexylamine) and DFMO (D, L α-diflouromethylornithine) was investigated. Application of polyamines, as a pre-treatment at 28°C for 2 h prior to heat-shock (45°C for 2 h), enhanced the recovery growth of both roots and hypocotyls. Treatment with polyamine biosynthetic inhibitors, that is, CHA and DFMO resulted in thermo sensitization, making seedlings vulnerable to heat-shock. Treatment of polyamines plus inhibitors reduced inhibitory effects and enhanced the growth recovery of seedling. Application of polyamines decreased electrolyte leakage and malondialdehyde from different tissue sections, suggesting protection of membrane integrity. Our results show that in comparisons with the heat-shock control, CaCl2 application in similar to PAs decreased electrolyte leakage and lipid peroxidation from root and hypocotyl tissue sections, and in contrast, in the presence of EGTA (a chelator of calcium), the stress injury intensified and growth were severely inhibited, and electrolyte leakage and MDA content of roots were significantly increased. We suggest that under stress conditions, polyamines may replace calcium in maintaining membrane integrity by binding to phospholipids of the membrane.