盐胁迫下腐胺调节黄瓜LHCII耗散过剩激发能的机制

In recent years, secondary salinization has become a major environmental factors that limiting production and quality of vegetable crop in protected cultivation in China. The photosynthetic efficiency of plants is significantly decreased when they are subjected to salinity, which severely affects yield and quality of crops. Polyamines, as new plant growth regulators, can relieve the inhibition of the photosynthetic efficiency in salt-stressed plants. In this study, the main protected horticulture crops-cucumber was used as experimental material. The light-harvesting complex (LHCII) of photosystem II was used for the study. The effects of exogenous putrescine on LHCII aggregation, energy quenching and excess excitation energy dissipation under salinity will be examined through separation and purification of LHCII by density gradient centrifugation, aided with chlorophyll fluorescence and spectroscopy techniques. The effects of Put on expression of LHCII protein and its mRNA under salt stress will be investigated using western blot and qRT-PCR technology. The study will reveal the protection mechanism of how exogenous Put alleviates the decline of photochemical efficiency in cucumber seedlings under salt stress on the level of membrane protein and gene. The outcome of this study will provide a theoretical basisi for applying exogenous polyamines to relieve salt injury and improve tolerance and growth of protected crop.

我国设施土壤次生盐渍化现象普遍存在，造成植株光合效率显著下降，生长发育受到抑制，严重影响设施作物的产量和品质。多胺作为一种新型的植物生长活性调节物质，能够缓解盐胁迫对植物光合效率的抑制。本项目以设施栽培作物黄瓜为试材，以类囊体膜上聚光色素蛋白复合体II（LHCII）为研究对象，通过分离、纯化LHCII，结合叶绿素荧光和光谱学技术，研究外源腐胺对盐胁迫下黄瓜叶片光能分配、LHCII聚集和过剩激发能耗散的影响；采用免疫印迹和qRT-PCR等技术，研究盐胁迫下腐胺处理对LHCII组分蛋白（LHCb1-6）及其编码基因表达特性的影响，并分析处理条件下LHCII上内源多胺的变化；深入揭示外源腐胺缓解盐胁迫下黄瓜幼苗光化学效率下降的光保护作用机制，为利用外源多胺促进设施作物优质高效生产和增强耐盐性提供理论依据。

我国设施土壤次生盐渍化现象普遍存在，导致植株光合效率显著下降，生长发育受到抑制，严重影响设施作物的产量和品质。腐胺（Put）作为一种新型的植物生长活性调节物质，能够有效缓解盐胁迫对植物光合效率的抑制。然而，对于Put如何调节过剩激发能耗散以缓解盐胁迫下黄瓜幼苗光化学效率抑制的具体机制仍不清楚。本试验以盐敏感型黄瓜品种‘津优4号’为试材，研究外源Put对盐胁迫下黄瓜叶片过剩激发能耗散、叶绿素代谢途径、LHCII组分蛋白及其编码基因表达、LHCII上内源多胺含量的影响，以期揭示Put缓解盐胁迫下黄瓜幼苗光化学效率抑制的光保护机制，为利用外源多胺促进设施作物生育和增强抗逆性提供理论依据。主要研究结果如下：. 1．喷施8mM Put显著提高了盐胁迫下黄瓜幼苗叶片的NPQ、类囊体膜的质子梯度（qE）以及能量耗散的状态转换（qT）水平，并有效缓解了盐胁迫下黄瓜幼苗叶片囊体膜叶绿素捕光能力和受激发能力的降低。. 2．外源Put促进UroIII向ProtoIX的转化，缓解了盐胁迫下叶绿素水平的降低。此外，Put处理降低了尿卟啉原III合酶、叶绿素酶和脱镁螯合酶的活性，下调了谷氨酰-tRNA还原酶、5-氨基乙酰丙酸脱水酶、尿卟啉原III合酶、尿卟啉原III脱羧酶和叶绿素a加氧酶的转录水平，但显著增加了叶绿素b还原酶、脱镁叶绿酸a加氧酶、红色叶绿素代谢物还原酶的转录水平。. 3． Put显著提高盐胁迫下黄瓜类囊体膜上D1、D2及Lhcb4蛋白的表达水平，而显著下调了盐胁迫下Lhcb3蛋白的表达水平。同时，Put显著上调盐胁迫处理前期（6 h）的黄瓜幼苗Lhcb1-6的基因表达水平，胁迫24 h后下调Lhcb的基因表达水平，其中，盐胁迫第7天对Lhcb1、Lhcb3、Lhcb5的下调比较显著。. 4．盐胁迫处理第3天，黄瓜LHCII三聚体上总的结合态多胺含量显著高于对照水平，而单体上总的结合态多胺水平低于对照水平；盐胁迫处理7 d 时，无论单体或三聚体LHCII的结合态多胺水平均低于对照。Put能够进一步增加盐胁迫下黄瓜幼苗叶片TGase的活性，并显著提高盐胁迫下黄瓜幼苗叶片LHCII三聚体和单体上内源游离态及结合态多胺含量。