南瓜砧木嫁接对低温下西瓜幼苗耐冷性、光合作用及抗逆基因表达的影响
Effects of pumpkin rootstock grafting on cold tolerance, photosynthesis and expression of stress tolerance genes of watermelon seedlings under chilling stress

为阐明南瓜砧木嫁接诱导西瓜幼苗产生低温抗性的适应机制，研究了南瓜砧木‘青研1号’嫁接对低温10℃/5℃（昼/夜）胁迫下西瓜自交系‘97103’幼苗生长、叶绿素荧光、光合气体交换、卡尔文循环和抗逆相关基因表达的影响。结果表明：低温胁迫下西瓜自嫁苗PSⅡ最大量子产量（Fv/Fm）等叶绿素荧光参数与常温对照相比显著下降。低温处理5 d后，西瓜自嫁苗和南瓜砧木嫁接苗PSⅡ有效量子产量（ΦPSⅡ）与常温对照相比分别下降92.9%和59.2%。南瓜砧木嫁接有效延缓了低温引起的PSⅡ损伤，同时促进卡尔文循环关键基因核酮糖1,5-二磷酸羧化/加氧酶（Rubisco）大亚基基因（rbcL）、3 磷酸甘油酸激酶基因（PGK）、磷酸核酮糖激酶基因（PRK）、果糖1,6 二磷酸激酶基因（FBPase）转录水平显著增加，保持低温下较高水平的CO2同化速率（Asat）。此外，南瓜砧木嫁接促使低温下西瓜叶片蒸腾速率下降，减缓叶片萎蔫、皱缩，同时诱导谷胱甘肽过氧化物酶（GPX）、抗坏血酸过氧化物酶（tAPX）、谷胱甘肽还原酶（GR）和脱水蛋白（ERD10）等9个抗逆相关酶基因上调表达，增强了植株抗氧化能力。低温处理5 d后，西瓜自嫁苗和南瓜砧木嫁接苗冷害指数分别为61.1%和22.2%，全株干质量与对照相比分别下降61.0%和 33.2%。南瓜砧木嫁接通过调节蒸腾作用，减少水分散失，促进卡尔文循环关键基因和抗逆相关基因表达，减缓PSⅡ光抑制，减轻膜脂过氧化损伤，增强西瓜对低温的适应能力。
The effects of pumpkin rootstock (‘Qingyan No.1’) grafting on growth,chlorophyll fluorescence,photosynthetic gas exchange,expression of Calvin cycle and stress tolerance genes of watermelon (‘97103’) seedlings under chilling stress (10℃/5℃) were studied to clarify the mechanism of photosynthetic adaptation involved in chilling tolerance in pumpkin rootstock grafted watermelon seedlings.The results showed that the chlorophyll fluorescence parameter such as maximum quantum yield of PSⅡ (Fv/Fm) in self grafted watermelon decreased significantly under chilling stress in comparison with control.After 5 days of chilling stress,the effective quantum yield of PSⅡ (ΦPSII) in self grafted watermelon seedlings and pumpkin rootstock grafted seedlings decreased by 92.9% and 59.2% compared with the control.Pumpkin rootstock grafting effectively delayed the damage of PSⅡ induced by chilling and promoted the expression of key genes including Rubisco large subunit (rbcL),glycerate 3 phosphate kinase (PGK),phosphoribulose kinase (PRK), and Fructose 1,6 bisphosphatase (FBPase) involved in Calvin cycle.A higher CO2 assimilation rate (Asat) in pumpkin rootstock grafted seedlings under chilling stress was observed.which was attributed to the enhanced expression of 9 stress tolerance genes including GPX, tAPX, GR, and ERD10.After 5 days of chilling treatment,the chilling injury index of self grafted watermelon seedlings and pumpkin rootstock grafted seedlings were 61.1% and 22.2%,respectively.The whole plant dry weight was decreased by 61.0% and 33.2%,respectively compared with the control.It is indicated that pumpkin rootstock grafting reduces the water loss by regulating transpiration,up regulates the expression of key genes involved in Calvin cycle and stress tolerance,thus alleviates photoinhibition of PSⅡand reduces the damage of membrane lipid peroxidation to enhance the adaptability of watermelon under chilling stress