Study Of The Promotion Of Cold-resistance Of Maize Seedings By Spermidine And Relationship With NO

In this dissertation, the effects of spermidine on the chilling tolerance in maizespecies (Nongda108) were investigated. In addition, the involvement of nitric oxide(NO) in spermidine-induced improvement of chilling tolerance was also elucidated.The main experimental results and conclusions were as follows:1. Eogenous application of0.4mmol/L spermidine relieved the inhibition effect of lowtemperature on the growth in maize seedings. Spermidine induced a significantlyincreased activity of antioxidant enzymes (SOD, POD, CAT) under chilling stresscondition and also markedly decreased the accumulation of hydrogen peroxide andsuperoxide anion. Thus, the membrane lipid peroxide levels were significantlydecreased. In addition, spermidine treatment blocked the chilling stress-induceddecrease of chlorophyll content and enhanced the content of proline, souble sugar.Furthermore, spermidine-treated seedlings exhibited an obviously increased mRNAand protein expression of heat shock proteins (HSP70and HSP90) under chilling stresscondition.These results obviously show that exogenous spermidine can improve thechilling tolerance in maize seedlings.2. his dissertation further investigated the role of NO in the process ofspermidine-induced improvement of chilling tolerance in maize seedlings. Spermidinesignificantly enhanced the production of NO in maize leaf cells. However, treatment ofsodium tungstate, which is an inhibitor of nitrate reductase, markedly inhibited theproduction of NO, and reversed the alleviation effects of spermidine under chillingstress. Sodium tungstate decreased the activity of antioxidant enzymes (SOD, POD,CAT), the membrane lipid peroxide level was significantly increased and the proline,souble sugar and chlorophyll content were decreased in maize seedlings. In addition,sodium tungstate also decreased the mRNA and protein expression of (HSP70andHSP90) under chilling stress. Furthermore, exogenous application of sodiumnitroprusside, which is a NO donor, significantly enhanced the NO level in bothcontrol and chilling-stressed maize leaf cells. At the same time, sodium nitroprusside treatment also enhanced the activity of antioxidant enzymes and the mRNA andprotein expression of (HSP70and HSP90) in chilling-stressed maize seedlings.Taken together, our results revealed that spermidine-induced improvement ofchilling tolerance in maize seedlings is mediated by nitrate reductase-dependent NOsignaling pathway, which contributed to the spermidine-induced enhancement ofantioxidant enzymes activity and the mRNA and protein expression of HSP70andHSP90.