低温胁迫下褪黑素对秋茄幼苗光合效率、碳同化以及激素的调控作用

Effects of melatonin on photosynthetic efficiency,carbon assimilation,and hormones of Kandelia obovata seedlings under low-temperature stress

为探明不同低温胁迫时间下褪黑素(MT)对秋茄幼苗光合效率、碳同化以及激素代谢的调控特征,本试验采用昼夜温差(8℃/-3℃)设置,进行为期2、4和6 d的低温胁迫处理,研究叶片喷施0.2 mmol·L^(-1) MT对秋茄幼苗叶片光合作用和内源激素平衡的调控作用。结果表明:随着低温胁迫时间的延长,MT对秋茄光合作用的调控作用表现先增后降,其中低温处理4 d时效果最优;在低温胁迫4 d,叶片喷施MT的秋茄幼苗叶片净光合速率(P_(n))、蒸腾速率(T_(r))、气孔导度(G_(s))、PSⅡ实际光化学效率(F_(v)/F_(m))、PSⅡ最大光化学量子产量(Ф_(PSⅡ))、光化学猝灭系数(qp)分别较低温处理增加13.67、2.40、1.48、2.03、1.42、2.00倍,而幼苗叶片胞间CO_(2)浓度(Ci)、非光化学猝灭系数(NPQ)分别降低76.29%和50.36%;幼苗叶片光呼吸速率(Rp)、CO_(2)饱和点(CSP)、羧化效率(CE)、RuBP最大再生速率(J_(max))分别较低温处理提高1.28、1.09、4.24、12.70倍;此外,秋茄幼苗叶片内源MT、生长素(IAA)、赤霉素(ABA)、脱落酸(GA)分别较低温处理增加1.23、1.24、1.17、1.61倍;叶片喷施MT能够提高低温胁迫下秋茄幼苗叶片光呼吸速率和光合碳同化能力,提高内源激素含量,增强秋茄幼苗的光合能力,减轻低温胁迫对植株的伤害,但其对低温胁迫的缓解效应与低温胁迫时间相关;秋茄幼苗内源MT与P_(n)、T_(r)、F_(v)/F_(m)、Ф_(PSⅡ)、R_(p)、CE、J_(max)、IAA、GA、ABA等均存在极显著正相关,表明内源褪黑素在调控光合效率、碳同化以及激素方面起到重要作用。

We assessed the regulatory role of melatonin(MT)on photosynthetic efficiency,carbon assimilation,and hormone metabolism of Kandelia obovata seedlings under different low periods.To investigate the protective role of MT in photosynthesis and endogenous hormone balance,we sprayed 0.2 mmol·L^(-1)MT on K.obovata seedlings subjected to low-temperature stress(8℃/-3℃)for 2,4,and 6 days.The results showed that,with increasing stress duration,the regulatory role of MT on photosynthesis of K.obovata seedlings first increased and then decreased,reaching a maximum under low-temperature stress for 4 days.After 4 days of low-temperature stress,spraying MT increased net photosynthetic rate(P_(n)),transpiration rate(T_(r)),stomatal conductance(G_(s)),actual photochemical efficiency of PS Ⅱ(F_(v)/F_(m)),maximum photochemical quantum yield of PS Ⅱ(Ф_(PSⅡ)),and photo-chemical quenching coefficient(q_(p))by 13.67,2.40,1.48,2.03,1.42 and 2.00 times,respectively.Spraying MT decreased the intercellular CO_(2) concentration(C_(i))and non-photochemical quenching coefficient(NPQ)of seed-lings by 76.29%and 50.36%,respectively.Furthermore,spraying MT increased leaf photorespiration rate(R_(p)),CO_(2) saturation point(CSP),carboxylation efficiency(CE),and maximum RuBP regeneration rate(J_(max))in seedlings by 1.28,1.09,4.24,and 12.70 times,respectively.In addition,leaf endogenous MT,auxin(IAA),gibberellin(ABA),and abscisic acid(GA)were increased by 1.23,1.24,1.17,and 1.61 times respectively in seedlings sprayed with MT under low-temperature stress for 4 days.In conclusion,foliar spraying MT could improve photorespiration rate and photosynthetic carbon assimilation ability of K.obovata seedlings under low-temperature stress,increase endogenous hormone content,enhance photosynthetic capacity,and reduce the damage of low-temperature stress.However,such mitigation effects were dependent on the duration of low-temperature stress.Endogenous MT was positively correlated with P_(n),T_(r),F_(v)/F_(m),Ф_(PSⅡ),R_(p),CE,J_(max),IAA,GA,and ABA,indicating that endogenous MT plays an important role in regulating photosynthetic efficiency,carbon assimilation,and hormones.