The Role And Mechanism Of Calcium Signal In Methyl Jasmonate-Enhanced Watermelon Tolerance To Cold Stress

Watermelon（Citrullus lanatus（Thunb.）Matsum.et Nakai.）is an important horticultural crop in China,which takes the first place in the production of melon and fruit vegetables in China.However,watermelon originated in tropical Africa,which likes temperature and heat resistance,and is sensitive to low temperature.When cultivated in protected cultivation during early spring,it is vulnerable to continuous cold in late spring,which greatly impacts the growth and development of watermelon seedlings and directly causes the reduction of yield and quality.Methyl jasmonic and calcium signaling play an essential role in plant resistance to low temperature stress,but the relationship between them is still unclear.Watermelon cultivar’nongkeda No.5’was used to study the effects of Exogenous methyl jasmonate（MeJA）on low temperature resistance,ClCBF gene expression,cytoplasmic Ca²⁺accumulation and calcium signal related gene expression of watermelon seedlings.On this basis,we further studied the effect of exogenous CaCl₂ on low temperature resistance of watermelon seedlings and the effect of calcium channel inhibitor LaCl₃ on MeJA mediated low temperature resistance,and preliminarily analyzed the role and mechanism of Ca²⁺in MeJA regulation of low temperature resistance of watermelon.The main results are as follows:1.Exogenous MeJA(200μmol·L^-1)could improve the chilling resistance of Watermelon Seedlings by improving antioxidant capacity,alleviating oxidative stress and improving photosynthetic capacity under low temperature stress.2.MeJA activated cytoplasmic Ca²⁺signal under low temperature stress.Therefore,the low temperature resistance induced by MeJA may be related to Ca²⁺signal.3.The low temperature resistance induced by Ca²⁺is related to the regulation of ClCBFs gene expression,and Ca²⁺signal mediates the induction of MeJA to ClCBF1 expression.