外源褪黑素对干旱胁迫下烤烟幼苗生长的缓解效应与生理机制研究

Alleviation of drought stress and the physiological mechanisms in tobacco seedlings treated with exogenous melatonin

为探究外源褪黑素(MT)在增强烤烟干旱胁迫耐受性中的作用,以耐旱型的‘豫烟6号’和干旱敏感型的‘豫烟10号’为材料,利用15%的聚乙二醇(PEG-6000)模拟中度干旱环境,研究干旱胁迫条件下叶面喷施不同浓度的MT(0,0.1,0.2,0.4mmol·L^-1)对烤烟幼苗的生长、叶绿素含量、光合特性、叶绿素荧光、抗氧化酶活性及活性氧代谢的影响。结果表明:干旱胁迫下外源MT处理可显著增加烤烟幼苗的总根长、总根表面积、根平均直径和根尖数;提高叶绿素含量、净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、水分利用效率(WUE)、PSⅡ最大光化学效率(Fv/Fm)、PSⅡ实际光化学效率(ΦPSⅡ)和光化学猝灭系数(qP),减缓叶片中胞间CO2浓度(Ci)和非光化学猝灭系数(NPQ)的升高,有效减轻干旱胁迫对烤烟幼苗叶片光合作用的气孔限制和非气孔限制;提高叶片中超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性,增强烟苗的抗氧化性能;降低丙二醛(MDA)含量和O2-^·产生速率,有效缓解干旱胁迫对膜的伤害,增强烟苗耐受性;其中干旱敏感型品种‘豫烟10号’变化幅度大于耐旱型品种‘豫烟6号’;随着外源MT浓度的增加,2个烤烟品种幼苗的生长指标均表现出先升高后降低的趋势,以叶面喷施0.2mmol·L^-1的MT对烟苗生长的促进效果最佳。因此,在干旱胁迫下,叶面喷施适宜浓度的MT能提高烟草幼苗对光能的捕获与转换,增强光合作用,促进烟苗的生长;并能够通过增强烟苗的抗氧化能力,缓解氧化伤害,从而增强烟草幼苗对干旱逆境的适应性,且对干旱敏感型品种‘豫烟10号’的效果更为显著。

This experiment explored the role of exogenous melatonin(MT)in enhancing the resistance of tobacco seedlings to drought stress.Moderate drought stress was simulated using 15%polyethylene glycol(PEG-6000),and the drought-tolerant variety‘Yuyan No.6’and drought-sensitive variety‘Yuyan No.10’were tested for their response following foliar-spraying with MT at concentrations of 0,0.1,0.2,and 0.4 mmol·L^-1.Parameters measured included seedling growth,chlorophyll content,photosynthetic characteristics,chlorophyll fluorescence,antioxidant enzyme activities and reactive oxygen metabolism of the tobacco seedlings.It was found that MT application significantly increased total root length,total root surface area,average root diameter and root tip number;enhanced both shoot and root fresh weight of tobacco seedlings under drought stress;increased chlorophyll content,net photosynthetic rate(P n),stomatal conductance(G s),transpiration rate(T r),water use efficiency(WUE),maximal PSⅡquantum yield(F v/F m),PSⅡactual photochemical efficiency(ΦPSⅡ)and photochemical quenching coefficient(q P);and decreased the enhancement of intercellular carbon dioxide concentration(C i)and non-photochemical quenching coefficient(NPQ).Moreover,the stomatal and non-stomatal limitations to photosynthetic ability were effectively reduced by exogenous MT in seedlings under drought stress.The application of MT enhanced the activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT);and reduced malondialdehyde(MDA)content and O 2-^·generation rate.The changes in drought-sensitive‘Yuyan No.10’were greater than those in drought-tolerant‘Yuyan No.6’.Across the range of exogenous MT concentration tested,the seedling growth indexes of the two tobacco varieties showed stimulation at lower rates and inhibition at higher rates.Foliar application with 0.2 mmol·L^-1 MT produced the largest growth promotion effects and drought stress alleviation.In summary,MT application at the appropriate concentration positively stimulated seedlings to capture and convert solar energy,thus promoting seedling photosynthesis and growth.Exogenous MT also enhanced the adaptability of seedlings to drought stress by improving antioxidant capacity and reducing oxidative damage.The positive effect of MT was more obvious for drought-sensitive variety‘Yuyan No.10’.