外源褪黑素对干旱胁迫下玉米幼苗根系发育及生理生化特性的影响

Effects of exogenous melatonin on root development and physiological and biochemical characteristics of maize seedlings under drought stress

为研究喷施外源褪黑素对玉米幼苗抗旱性的效果,探究褪黑素缓解干旱胁迫的作用机理。以玉米品种郑单985作为供试材料,采用水培试验,使用聚乙二醇(PEG-6000)模拟干旱胁迫,探究干旱胁迫下不同浓度(0、10、50、100μmol·L^(-1))褪黑素对玉米幼苗生长、根系构型及分级特征、光合特性、抗氧化能力和渗透调节物质含量等指标的影响,采用隶属函数值法对不同处理下玉米幼苗的抗旱性进行综合评价。结果表明:与不施褪黑素处理相比,喷施50μmol·L^(-1)褪黑素效果最优,玉米幼苗的株高、地上部鲜重和干重、地下部鲜重和干重、茎耐受指数和根耐受指数均显著增加;玉米幼苗的总根长(RL)、根表面积(SA)、根体积(RV)和根尖数(RT)均显著增加,RL的Ⅰ级(RD 0~0.5 mm)、SA的Ⅰ和Ⅱ级(RD 0.5~1.0 mm)、RV的Ⅰ和Ⅱ级均显著提高,其中50μmol·L^(-1)褪黑素处理中的根系Ⅰ级径级区间的RL和SA占该处理根系的总比例最高,达到82.40%和47.32%;地上部丙二醛(MDA)含量显著降低了20.17%;地上部可溶性蛋白含量增加至最大,地下部可溶性蛋白含量显著升高了49.14%;光合速率(Pn)和气孔导度(Gs)分别增加了85.83%和32.81%;地上部和地下部超氧化物歧化酶(SOD)活性、地上部过氧化物酶(POD)活性、地上部过氧化氢酶(CAT)活性和地上部抗坏血酸过氧化物酶(APX)活性均显著升高;干旱胁迫下4个处理的抗旱性强弱排序为50μmol·L^(-1)(MT50)>10μmol·L^(-1)(MT10)>100μmol·L^(-1)(MT100)>0μmol·L^(-1)(MT0),即MT50处理的抗旱性最强。外源喷施50μmol·L^(-1)褪黑素有效调节了玉米幼苗地上部和地下部的抗氧化酶活性和渗透调节能力,减少了MDA含量,提高了地上部的光合作用能力,调节了玉米幼苗地上部和地下部的可溶性蛋白含量、抗坏血酸(As A)含量、谷胱甘肽(GSH)含量、SOD活性、POD活性、APX活性和CAT活性,提高了玉米幼苗地上部和地下部的生物量和伸长量,减轻了干旱胁迫对根系构型的影响,提高了玉米幼苗的抗旱性,为研究褪黑素缓解干旱胁迫的作用机理提供了理论依据。

This research studied the effect of spraying exogenous melatonin on drought resistance of maize seedlings,and explored the mechanism of melatonin alleviation of drought stress in maize variety Zhengdan 985.A hydroponic experiment was conducted,using polyethylene glycol(PEG-6000)to simulate drought stress.The effects of melatonin at different concentrations(0,10,50,100μmol·L^(-1);MT0,MT10,MT50,MT100,respectively)on the growth,root configuration and diameter characteristics,photosynthetic characteristics,antioxidant capacity and osmotic content of maize seedlings under drought stress were studied.Multivariate analysis of the maize seedling drought resistance under the various treatments was undertaken using the subordinate function value method.Compared with the treatment without melatonin,spraying 50μmol·L^(-1)melatonin had the best effect,and significantly increased plant height,aboveground fresh and dry weight,underground fresh and dry weight,stem tolerance index and root tolerance index of the seedlings.The total root length(RL),root surface area(SA),root volume(RV)and root tip number(RT)of maize seedlings were also increased significantly by melatonin application.The RL of the finest diameter category(0-0.5 mm)and the SA and RV of the second diameter category(0.5-1.0 mm),were also significantly increased.Across the treatments,the proportions of total RL and SA(82.40%and 47.32%,respectively)in the(0-0.5 mm)diameter range were highest in the 50μmol·L^(-1)melatonin treatment.In this treatment,compared to the control,shoot malondialdehyde(MDA)levels were decreased by 20.17%(P<0.05),shoot soluble protein content was maximized,the soluble protein content of underground parts was increased by 49.14%,and leaf photosynthetic rate(Pn)and stomatal conductance(Gs)were increased by 85.83%and 32.81%,respectively.The activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)and ascorbate peroxidase(APX)in shoots and underground organs were also significantly increased.The order of drought resistance of the four treatments under drought stress was MT50>MT10>MT100>MT0.Exogenous application of 50μmol·L^(-1)melatonin effectively regulated the activities of antioxidant enzymes and osmotic regulation in the aboveground and underground parts of maize seedlings,reduced the MDA content,increased the photosynthetic capacity,and beneficially regulated the soluble protein content,ascorbate(AsA)content,glutathione(GSH)content,SOD activity,POD activity,APX activity and CAT activity in the aboveground and underground parts of maize seedlings.The biomass and elongation of maize seedlings were increased,the detrimental effect of drought stress on root configuration was reduced,and the drought resistance of maize seedlings was improved.These results provide a theoretical basis for revealing the mechanism of melatonin alleviation of drought stress.