黄瓜叶片衰老过程中脂滴的原位降解和液泡内降解

Cucumber Leaf Senescence Causes in-situ and Vacuolar Degradation of Lipid Droplets

对黄瓜不同发育阶段叶片中的脂滴进行超微观察,以期了解衰老叶内脂滴降解的场所。结果表明,衰老叶片中部分质体小球在叶绿体内降解,降解先从小球一侧开始,向另一侧推进。衰老叶片含有胞质脂滴,有些胞质脂滴紧贴叶绿体,显示其发生与叶绿体密切相关;有些胞质脂滴与液泡密切接触,并向液泡内转运,进入液泡后发生降解。显然,黄瓜叶衰老不仅引起脂滴在液泡内降解,也引起脂滴在叶绿体内原位降解,证明液泡并不是脂滴降解的唯一场所。

Leaf senescence induces up-regulated expression of lipid degradation-related genes,and activities of lipases are found to be enhanced in vacuoles. However,it is not clear whether vacuoles are the only site for the degradation of lipid droplets. Therefore,dynamics of lipid droplets in cucumber leaves of different developmental stages were investigated by means of transmission electron microscopy to understand the sites for lipid droplets caused by leaf senescence. Some plastidial lipid droplets in senescent leaves were demonstrated to undergo degradation inside chloroplasts. Degradation began from one side and then expanded to the other. In the cytoplasm some cytosolic lipid droplets were found to be attached to the surface of chloroplasts,indicating that their occurrence might have a close relation to chloroplasts. Some cytosolic lipid droplets revealed a close association with vacuoles,indicating that they were on the pathway to be transported into the vacuoles. Lipid droplets underwent degradation after they were transported into vacuoles. Apparently,cucumber leaf senescence caused in-situ degradation of plastidial lipid droplets and vacuolar degradation of cytosolic lipid droplets. These observations proved that vacuoles are not the only site for the degradation of lipid droplets.