珊瑚豆果实成熟过程中叶绿体转化为杂色体的研究

STUDIES ON THE CONVERSION OF CHLOROPLAST TO CHROMOPLAST DURING FRUIT RIPENING IN SOLANUM PSEUDO CAPSICUM VAR.DIFLORUM

珊瑚豆 (Solanum pseudo- capsicum var.diflorum (Vell.) Bitter)果实成熟过程中 ,果实颜色的变化和叶绿素含量降低及类胡萝卜素含量增长相符合。对果实中叶绿体转化为杂色体进行了电镜观察。早期绿色果实的特点是叶绿体具典型的基粒 -基粒间类囊体结构。在黄绿色果实时期叶绿体类囊体系统解体 ,代之以少数非叶绿素的单个类囊体和积累大的嗜锇的质体小球。质体转变为所谓的原质体。这表明叶绿体在果实成熟中的脱分化过程。当果实达到黄色阶段 ,这些质体所含的质体小球开始从中央形成质体小管的结构。最初质体小球中央变为半透明 ,认为是质体累积胡萝卜素的开始。随着质体小球的延长 ,小管从小球中伸出。这些小管围以电子致密的膜 ,中央是半透明的轴心。与此同时 ,在质体基质中出现一系列发育不同阶段的小泡 ,似乎是形成新的质体小球的过程。在成熟的橙色和橙红色果实中的杂色体中只包含无数小管和小的质体小球。质体小管在数量和长度上增长 ,充满成熟的杂色体。无数质体小球分布在小管之间的空间中。成熟杂色体从脱分化的原质体的重建是真正的再分化过程。可以作出结论 。

Determination of chlorophyll and carotenoid contents in the ectocarp during fruit ripening in Solanum pseudo capsicum var.diflorum (Vell.) Bitter revealed that the changes of fruit colour coincided with the decline of chlorophyll and the increase of carotenoid contents.The conversion of chloroplasts to chromoplasts in the fruit was studied by electron microscopy. The early green fruit was characterized by chloroplasts with a typical grana intergranal thylakoid structure.At yellow green fruit stage the thylakoid system was disinte grated and replaced by few non chlorophyllous single thylakoids, with accumulation of large osmiophilic plastoglobules. The plastids developed as the so called proplastids.These indi cated dedifferentiation of chloroplasts in a ripening fruit. When the fruit reached its yellow stage, numerous large plastoglobules contained in the young chromoplasts frequently showed transitional changes to plastid tubule structure.At first, the center of plastoglobules became semi translucent.It was believed that the young chromoplast were in an initial state of carotenoid deposition, followed by plastoglobules elongation and tubule protrution from the globules.These tubules were surrounded with an electron dense membranous sheath leaving the core semi translucent.Concurrently a series of vesicles in different developmental stages appeared from the stroma of the plastid, likely representing a process of formation of numerous small new plastoglobules.In the chromoplasts of a ripe orange or orange red colored fruit only numerous tubules and small plastoglobules were present.The plastid tubules increased in number and elongated in length filling the mature chromoplast.Numerous small plastoglobules also increased and distributed in the spaces between tubules.These results indi cated that the reconstruction of a mature chromoplast from a dedifferentiated plastid was really a form of redifferentiation, and it might be concluded that the conversion of chloroplast to chromoplast in the fruit of S.pseudo capsicum var.diflorum, in fact, was a processes of dedifferentiation and redifferentiation.