韧皮部环割诱导下的花花柴衰老机制

Senescence mechanisms induced by phloem girdling in Karelinia caspia

衰老是植物器官和组织发育的最后阶段,是一个受到严格控制的高度协调过程,其中碳水化合物浓度对衰老的影响十分显著。花花柴(Karelinia caspia)是塔克拉玛干沙漠南缘策勒绿洲的主要植物种,为了研究花花柴在韧皮部环割后的碳水化合物变化和叶片衰老过程,对其进行韧皮部环割,测量叶片光合色素含量、光合速率、可溶性糖含量、淀粉含量、脱落酸(ABA)含量和叶水势。结果表明:(1)环割能够诱导花花柴叶片的衰老,而诱导叶片衰老的主要因素有:叶片碳水化合物的积累、叶片ABA含量的上升,以及叶片水分状况的恶化。(2)相比于自然衰老,环割诱导的衰老导致许多正常的生理过程受到破坏。(3)类胡萝卜素在衰老过程中主要起光保护的作用。(4)韧皮部半环割也导致花花柴各种生理指标显著下降,表明植物无法通过增加剩余部分韧皮部筛管的运输通量而达到维持整个韧皮部运输系统顺畅的目的。

Aims Senescence constitutes the final stage of a plant＇s organ and tissue development, and is subject to gene control and strict regulation. Plant senescence is largely influenced by carbohydrate content and phloem girdling can induce leaf senescence. Our general objective is to study the effect of stem girdling on physiological condi- tions in Karelinia caspia. Specifically, we want to know the senescence processes after phloem girdling. In addi- tion, we also want to know the possible mechanisms for the senescence processes. Methods Three different types of girdling treatments, normal branch, semi-girdling, and full-girdling were performed on K. caspia. Twenty days after girdling, photosynthetic pigments content, photosynthetic rate, soluble sugar content, starch content, abscisic acid （ABA） content, and leaf water potential were measured. Important findings Phloem girdling can largely induce leaf senescence in K. caspia, and the reasons for leaf senescence may be as follows： girdling resulted in carbohydrate accumulation in leaf which subsequently led to ＂carbon feast＂ induced leaf senescence; girdling caused ABA accumulation in leaf and then resulted in senes- cence; girdling decreased water status, which may be another reason for leaf senescence. Compared with natural senescence, girdling induced senescence was a disorder and disorganized process, only a limited physiological process can be controlled by senescence related gene in the girdling induced senescence process. The most im- portant role for carotenoids in the senescence process is to protect the photosynthetic apparatus from being dam- aged by excess light and reactive oxygen species. Many physiological indicators declined in the semi-girdled K. caspia leaves just like full-girdled leaves, indicating that portion （e.g. half） of the phloem cannot undertake the transport flux which was done by the whole phloem sieve.