可溶性糖累积延缓生菜采后衰老黄化糖信号作用机制

Senescence and yellow are key factors that result in postharvest losses and limit the shelf life of leafy vegetables during storage and sale. Our previous researches found that light exposure during storage could significantly induced soluble sugar accumulation and inhibited chlorophyll degradation, and thus delayed postharvest senescence and yellow of lettuce. In the past, most studies demonstrated that soluble sugar played a role of respiratory substrate and energy in preserving fruits and vegetables postharvest quality. However, recent literatures indicate sugar involved in the regulation of plant growth and senescence as a signal substance. The aim of this project will reveal sugar signalling transduction pathway mechanism of soluble sugar affecting postharvest senescence and yellowing of lettuce during storage. The study firstly reveal the regular pattern of soluble sugar accumulation induced by light treatment in lettuce, and then clarify effects of sugar accumulation on postharvest senescence and yellowing of leaves. The main tasks is to focus on dependent and/or independent hexokinase (HXK) sugar signaling transduction pathway by comparing the effect of sugar and sugar analogues on downstream genes such as sugar signaling gene, senescence gene, chlorophyllase genes expression and senescence and yellowing indexes reponses during storage. The results obtained will not only theoretically enrich the sugar signaling mechanism of soluble sugar, but also practically provide scientific data for application of light exposure treatment in preservating of fruits and vegetables.

衰老黄化是导致绿叶蔬菜采后损失和限制其贮运与销售的关键因素。我们前期研究表明，光照处理显著诱导采后生菜可溶性糖累积，抑制叶绿素降解，延缓其衰老黄化，因此推测累积的可溶性糖可能参与调控叶片衰老黄化进程。以往国内外主要从呼吸底物和能量代谢角度研究糖的保鲜作用，近年来研究证实糖也作为一种信号物质参与植物生长和衰老调控。本项目拟以生菜为试材，采用叶圆片培养方法，从信号转导途径探讨糖累积对生菜衰老黄化的调控机制。研究首先揭示光照诱导采后生菜可溶性糖累积规律，阐明糖累积调控叶片衰老黄化进程；在此基础上从依赖和不依赖己糖激酶（HXK）信号转导途径研究糖和糖类似物能否激发糖信号基因、衰老基因、叶绿素酶基因等下游基因表达和衰老黄化参数应答，从而在物质代谢、酶活性和基因水平上解析糖累积对生菜衰老黄化调控的糖信号依赖途径。研究结果为糖对果蔬保鲜信号作用机制增添新内容，也为光照技术在果蔬保鲜中的应用提供科学依据。

衰老黄化是导致绿叶蔬菜采后损失和限制其贮运与销售的关键因素。为了探讨光照处理及其诱导的可溶性糖累积对采后叶片衰老黄化的影响，本项目从糖信号转导途径探讨可溶性糖对叶片衰老黄化的调控机制。研究首先揭示光照处理诱导采后叶片可溶性糖累积，在此基础上从是否依赖己糖激酶（HXK）信号转导途径研究可溶性糖（葡萄糖）对采后叶片糖信号调控作用。结果表明：（1）和黑暗对照相比，光照处理显著诱导/维持采后大宗绿色蔬菜（生菜、菠菜、芹菜、西兰花）葡萄糖、蔗糖、果糖、阿拉伯糖等可溶性糖累积，可溶性糖累积水平和蔬菜组织黄化指数负相关；（2）外源葡萄糖能够维持采后绿色蔬菜（生菜，西兰花）叶片叶绿素含量、叶绿素SPAD值、叶绿素前体合成物质原卟啉、Mg-原卟啉和原叶绿素酸酯相对含量，维持西兰花内可溶性糖浓度，降低其黄化指数，且无论是外源葡萄糖浓度还是样品中内源葡萄糖含量都和黄化指数呈显著负相关（R=-0.958（P<0.01）和R=-878（P<0.01）），说明葡萄糖累积对延缓采后蔬菜衰老黄化具有积极的调控作用。（3）针对可溶性糖是否通过依赖己糖激酶(HXK)信号转导途径调控采后叶片衰老黄化进程问题，比较研究糖（葡萄糖）、糖类似物甘露糖和3-O-甲基葡萄糖对采后生菜叶片采后衰老和抗氧化相关参数，结果发现：葡萄糖和甘露醇处理延缓采后生菜叶片黄化进程，其处理样品中叶绿素a和总叶绿素含量、叶绿素合成前体物质含量显著高于对照，抗氧化物质含量、抗氧化酶活性以及抗氧化能力大小也显著高于对照样品，且葡萄糖和甘露糖处理组之间变化趋势相似，无显著差异,而3-O-甲基葡萄糖对上述参数影响不显著，其和对照变化趋势相似,说明葡萄糖可能通过己糖激酶信号转导途径调控采后绿色蔬菜衰老黄化。综上，本研究在理论揭示光照处理保鲜果蔬的物质基础，补充完善可溶性糖保鲜的糖信号作用机制，在实践上为探索开发新的保鲜技术提供依据。