干旱胁迫条件下外源褪黑素提高小麦穗花发育和穗粒数的机理

Mechanism of exogenous melatonin improving the development of spike and floret and grain numbers per spike in wheat under drought stress

【目的】探究外源褪黑素(melatonin,MT)对水分胁迫下小麦穗花发育及抗氧化能力的调控效应,为采用化控方法有效缓解干旱胁迫对小麦的危害提供技术支撑。【方法】以多穗型品种‘豫麦49-198’和大穗型品种‘周麦22’为试验材料,设置3种土壤含水量处理:田间持水量的70%~80%(W1)、60%~70%(W2)、50%~60%(W3)。在小麦小花退化高峰期前进行叶面喷施100μmol/L外源MT处理,并以清水为对照(CK),自叶面喷施MT 3天起至开花期,每3天取1次样,在EMZ-TR解剖镜下观察小麦主茎幼穗分化进程,记录分化小花数、可孕小花数及小花分化各阶段特征。然后将小麦植株分为茎(茎+叶鞘)、叶、穗三部分,调查干重、含水量、顶展叶片过氧化氢(H_(2)O_(2))和丙二醛(MDA)含量,以及抗氧化相关酶(SOD、POD)活性。【结果】与W1处理相比,W2和W3处理下两品种小麦小花总分化小花数、退化结点小花数、可孕小花数和穗粒数均降低,同时小麦植株含水量下降,顶展叶片H_(2)O_(2)和MDA含量升高。喷施外源MT可以改善两品种小麦小花发育质量,减少小花退化,增加退化结点小花数、可孕小花数,提高结实穗粒数,对品种周麦22的促进效应高于豫麦49-198。外源MT有效降低了小麦顶展叶片H2O2和MDA含量,其中豫麦49-198和周麦22的H2O2降幅分别为6.83%~15.16%、7.60%~17.06%,MDA降幅分别为5.80%~15.31%、6.94%~16.83%;有效提高了两品种顶展叶片SOD和CAT抗氧化酶活性,豫麦49-198和周麦22的SOD活性提升幅度分别为4.25%~13.39%和5.62%~14.49%,CAT活性提升幅度分别为4.86%~15.68%和5.42%~16.50%,对品种周麦22的调控效应高于豫麦49-198。喷施外源MT有效提高了两品种小麦抗氧化能力和抗旱性,进而促进干物质生产和提高穗器官干物质积累量,在喷施处理后第15天时,豫麦49-198和周麦22喷施MT处理的穗器官干物质积累量相比于喷施清水处理分别平均提高6.66%~11.72%和8.06%~12.52%,为小花的生长发育提供了营养物质保障。【结论】在小麦小花退化高峰前喷施外源MT可以有效改善植株水分状况,提高干旱胁迫下小麦叶片的抗氧化能力和叶片质膜的稳定性,近而提升小麦物质生产能力,为小花发育和结实提供充足的营养保障,提高可孕小花数和结实穗粒数。

【Objectives】Exogenous melatonin(melatonin,MT)is capable of increasing the stress resistance of crops.We studied the mechanism of MT on the drought resistance of wheat from the aspects of development of spike and floret.【Methods】A field experiment was conducted using a multi-spike cultivar‘Yumai 49-198’and a large-spike cultivar‘Zhoumai 22’as experimental materials.Three soils were watered to 70%-80%,60%-70%,and 50%-60%of field water capacities to simulate the treatments of normal(W1),mild and moderate drought stress(W2,and W3),respectively.Before the peak of floret degradation,the wheat under each water condition was foliar sprayed with 100μmol/L melatonin(MT)and clear water control(CK),respectively.The development of floret and spikelet in the main stems were observed since the 3rd day of MT treatment,with frequency of every three days until the end of flowering stage,and the plant water content,hydrogen peroxide(H2O2)and malondialdehyde(MDA)contents,and enzyme activities were determined at the same time.【Results】Compared with W1 treatment,W2 and W3 treatments reduced the total number of differentiated florets,the numbers of degenerated nodal florets and fertile florets,and the grain number per spike in both wheat cultivars,and led to a decrease in the water content of wheat plants,and an increase in the content of H2O2 and MDA in top spread leaves.MT treatment improved the quality of floret development,reduced floret degradation,increased the number of degraded nodal florets,fertile florets and grains in fruiting spikes in both cultivars,and the promotional effect on cultivar Zhoumai 22 was higher than on Yumai 49-198.MT treatment effectively reduced leaf MDA and H2O2 contents by 5.80%-15.31%and 6.83%-15.16%in Yumai 49-198,and by 6.94%-16.83%and 7.60%-17.06%in Zhoumai 22,increased the activities of SOD and CAT by 4.25%-13.39%and 4.86%-15.68%in Yumai 49-198,and by 5.62%-14.49%and 5.42%-16.50%in Zhoumai 22,respectively,and the regulatory effect on Zhoumai 22 was higher than on Yumai 49-198.MT treatment was recorded significant promotion effect on dry matter production and accumulation in spike organs,the dry matter accumulation was improved by 6.66%-11.72%in Yumai 49-198 and 8.06%-12.52%in Zhoumai 22 on the 15th day of MT treatment.【Conclusions】Spraying exogenous melatonin before the peak of wheat floret degradation effectively increases the water content of top spread leaves,and thus increases the antioxidant system activity and maintains the stability of leaf cell membrane structure,alleviates drought damage to the plant and improves dry matter production for the requirement for floret development and grain setting,expressed as improved number of fertile florets and the grain number per spike.