可溶性糖延缓青花菜采后黄化的作用机制研究

Broccoli deteriorates very quickly after harvest because of senescence and the consequent yellowing of its sepals. These are extensive works related to methodologies in delaying yellowing during senescence of broccoli. Our previous research confirmed that the levels of soluble sugars were closely related to the chlorophyll degradation of broccoli. However, the mechanism involved remains to be further investigated. Thus, the purpose of this proposal is explore the effects of various concentrations soluble sugars treatments on suppressing postharvest senescence and yellowing of broccoli, which is focusing on the chlorophyll degradation, sugar and energy metabolism. The storage of the whole floral heads combined with the buds of broccoli in vitro culture will be applied, and try to reveal the possible mechanism of exogenous soluble sugars in delaying chlorophyll degradation of broccoli through the sugar signals and energy metabolism. Results from this research will not only illustrate thoroughly the mechanism of senescence and chlorophyll degradation of postharvest broccoli, but also provide theoretical basis for controlling senescence and yellowing in green vegetables and extending the storage period.

青花菜采后极易衰老而黄化，如何延缓其黄化的发生，一直是人们关注和研究的重点。我们前期研究证实，可溶性糖含量与青花菜叶绿素降解密切相关，但其作用机制尚不明确。因此，本项目以青花菜采后叶绿素降解、糖代谢和能量代谢为核心研究内容，采用整体花球贮藏与花蕾离体培养相结合的研究方法，分析不同种类外源可溶性糖处理对青花菜采后衰老黄化的抑制作用，并进一步从糖信号和能量代谢的角度，探讨可溶性糖在延缓青花菜采后叶绿素降解中的可能作用机制。本项目研究成果不仅有助于深入阐明青花菜采后衰老和叶绿素降解机理，也为在生产上控制绿色蔬菜的衰老黄化和延长贮藏期提供理论依据。

不同可溶性糖（蔗糖、葡萄糖和果糖）处理青花菜花球，结果发现，糖处理组能有效地延长青花菜货架期，延缓叶绿素的降解，色泽角（H）值的下降和明度（L*）值的上升，提高总酚含量，DPPH自由基清除能力、SOD、APX、PAL和CAT活性，降低POD活性；蔗糖处理还能够有效地抑制青花菜总硫代葡萄苷和萝卜硫素含量的下降；采后1-MCP（1-甲基环丙烯）处理能有效延缓青花菜叶绿素降解，同时维持较高的蔗糖、果糖和葡萄糖水平，可能直接或间接影响着蔗糖运载和糖代谢相关基因的表达。另外，采用三种不同糖（蔗糖、葡萄糖和果糖）培养离体青花菜花蕾，发现果糖能维持较高水平CAT和APX活性，蔗糖则保持最高的POD、SOD活性，三种糖均能维持离体青花菜较高水平的总糖含量、总黄酮含量，提高DPPH自由基清除率，保持了青花菜较好的品质。另外，蔗糖处理能维持能量代谢，维持较高的ATP、能荷水平，为保持抗氧化能力提供能量，并且对抑制线粒体、叶绿体膜损伤，延缓叶绿素的降解起到了一定的作用；葡萄糖和果糖处理则能通过调控糖代谢相关酶活性来维持较高水平的糖含量，从而抑制青花菜的衰老；蔗糖和甘露糖处理能有效延缓离体青花菜叶绿素的降解，蔗糖处理通过抑制叶绿素酶活性但甘露糖处理不能调控。这些结果说明，蔗糖和甘露糖通过PPP途径（如HXK）调控叶绿素代谢，蔗糖和甘露糖也可以对青花菜糖代谢相关基因（BoINV、BoHXK1和BoHXK2）进行调控。但是有关叶绿素代谢和糖代谢之间的关系值得进一步的探索。