外源Spd对低温胁迫下甜瓜幼苗光合与抗氧化特性及其相关基因表达的影响

摘要

为探讨外源亚精胺(Spd)诱导甜瓜耐低温胁迫的生理与分子机制,该研究以甜瓜耐低温品种‘世纪蜜’和低温敏感品种‘GL-1’为试验材料,在人工气候箱内采用基质栽培法,对其叶面喷施外源Spd,对低温胁迫及恢复后甜瓜幼苗生长、光合作用、抗氧化酶活性等生理指标进行测定,并利用定量PCR技术分析4种抗氧化酶基因在低温胁迫条件下的表达特性,分析外源Spd缓解低温胁迫的效应.结果表明:(1)低温胁迫显著抑制甜瓜幼苗的生长及其光合作用,降低幼苗叶绿素含量,显著增强抗氧化酶活性及相关基因表达水平,且对品种‘GL-1’影响大于‘世纪蜜’.(2)外源Spd处理可以有效促进甜瓜幼苗的生长,提高叶片叶绿素含量、净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、气孔限制值(Ls)、水分利用效率(WUE),以及最大光化学效率(Fv/Fm)、光系统Ⅱ光能捕获效率(Fv'/Fm')和表观光合电子传递速率(ETR),降低胞间CO2浓度(Ci)和初始荧光(Fo).(3)外源Spd可诱导低温胁迫下甜瓜抗氧化酶活性和基因表达量发生改变,并提高了低温胁迫下甜瓜幼苗叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)和抗坏血酸过氧化酶(APX)基因的表达,从而增强这些抗氧化酶活性,有效缓解低温胁迫造成的氧化胁迫伤害.(4)与对照相比,外源Spd对低温胁迫下品种‘GL-1’各指标降低或升高的幅度大于品种‘世纪蜜’.研究发现,Spd有利于甜瓜幼苗在低温胁迫下光合作用的维持,提高光合电子传递效率、光能的捕获与转换,并提高抗氧化酶活性和相关基因表达水平,促进甜瓜幼苗的生长,有效缓解低温胁迫对甜瓜幼苗生长的抑制作用,且Spd对低温敏感品种‘GL-1'缓解效果优于耐低温品种‘世纪蜜’.%In order to investigate the effects of exogenous spermidine (Spd) on the physiological and molecular mechanism of melon seedlings under chilling stress,we carried out the experiment using the melon varieties ‘Shijimi’ (chilling-tolerant) and ‘GL-1’ (chilling-sensitive) in climate chambers and substrates to investigate the alleviating effects of Spd on melon seedlings for growth,photosynthesis and reactive oxygen metabolism.The expression patterns of four different antioxidant enzyme genes were analyzed using quantitativePCR under chilling stress and recovery.The results showed that:(1) the growth,photosynthesis and chlorophyll contents of melon seedlings were decreased under chilling stress,the antioxidant enzyme activities and the expression patterns of four different antioxidant enzyme genes were increased,and the influence on ‘GL-1’ was greater than that on ‘Shijimi’;(2) Spd could increase melon-seedling growth,chlorophyll contents,net photosynthetic rate (Pn),stomatal conductance (Gs),transpiration rate (Tr),stomatal limitation (Ls),water use efficiency (WUE),maximum photochemical efficiency (Fv/Fm),light energy capture efficiency of photosystem Ⅱ (Fv'/Fm') and the apparent electron rate(ETR),while reduce intercellular carbon dioxide concentration (C1) and initial fluorescence (Fo) under chilling stress;(3) Spd changed antioxidant enzyme activities and gene expression patterns under chilling stress.The expression of superoxide dismutase (SOD),catalase (CAT),peroxidase (POD) and ascorbate peroxidase (APX) genes increased and antioxidant enzyme activities were improved,and the injury of chilling stress was reduced.(4) Compared with the control,Spd decreased or increased the indexes of ‘GL-1’under low temperature stress more than that of ‘Shijimi’.Obviously,Spd was favorable for the melon seedlings to maintain photosynthesis,improve photochemical electron transport efficiency,capture and converse solar energy,the antioxidant enzyme activities and the expression patterns of antioxidant enzyme genes,and thus melon growth were improved,and inhibition of chilling stress on melon was reduced.These findings suggested that ameliorative effect of Spd on melon seedlings under chilling stress was effective,especially for chillingsensitive genotypes.