Melatonin was involved in low temperature resistance of wild watermel-on rootstock in regulating scion

GUO Kai; LIU Jiahe; LAN Zhixiang; LIU Haiheng; LI Hao

doi:10.16861/j.cnki.zggc.2024.0674

Abstract：To elucidate the mechanism of TC rootstock enhances low-temperature tolerance in grafted watermelon,this study investigated the cold stress responses of wild watermelon germplasm TC and cultivated variety Nongkeda No.5(N5).The results demonstrated that TC plants exhibited significantly less stress-induced damage than N5 following low-temperature treatment.Grafting with TC rootstock markedly reduced malondialdehyde(MDA)accumulation and elec-trolyte leakage in N5 scions under cold stress,while concurrently enhancing melatonin levels in the scions.Exogenous melatonin application increased antioxidant enzyme activity in both self-grafted(N5/N5)and heterografted(N5/TC)plants under low-temperature conditions.Although melatonin treatment showed no significant effects on CBF1 expression com-pared to deionized water control,it remarkably up-regulated CBF2 and CBF3 expression levels to 7.68-fold and 25.71-fold in N5/N5 plants,respectively,significantly activating these key cold-adaptation genes.Notably,TC rootstock intrinsically induced CBF1-3 expression but paradoxically suppressed melatonin biosynthesis in N5/TC grafts.This dual regulation resulted in decreased photosynthetic rates and elevated MDA content in N5/TC plants under cold stress.Our findings reveal that TC rootstock enhances cold tolerance through melatonin-mediated up-regulation of CBF gene expres-sion,establishing melatonin's pivotal role in TC-induced cold resistance.This research provides valuable insights for se-lecting optimal rootstock to mitigate chilling injury in early spring watermelon cultivation.