Nitric oxide mediates abscisic acid induced thermotolerance in the calluses from two ecotypes of reed under heat stress

Calluses from two ecotypes of reed (Phragmites communis Trin.) plant (dune reed) [DR] and swamp reed [SR]), which show different sensitivity to heat stress, were used to study plant acclimations to heat stress involved with ABA and NO. High temperature induced ion leakage and accumulation of MDA in two calluses, which were significantly alleviated by exogenous ABA and NO application. Pretreatment with fluridone, L-NNA or cPTIO obviously aggravated ion leakage and the accumulation of MDA in DR callus under heat stress whereas had no effect on SR callus. Moreover, endogenous NO and ABA contents and NOS activity increased markedly under heat stress in DR callus while remained stable in SR callus. Further research on two calluses indicated that inhibition of NO accumulation by cPTIO and L-NNA blocked the protective effect of exogenous ABA whereas inhibition of ABA synthesis by fluridone had no influence on the protective effect of exogenous NO. In DR callus, exogenous ABA treatment resulted in further increase of NOS activity and NO release in comparison with that of heat stress alone while fluridone treatment inhibited the increase of NOS activity and NO release under heat treatment. In contrast, both exogenous NO treatment and inhibition of endogenous NO accumulation by cPTIO and L-NNA had no influence on ABA content. In conclusion, NO might act as an intermediate molecular mediating abscisic acid induced thermotolerance under heat stress.