engleski

Differentiation of chromoplasts in Cucumis sativus petals

The development of fibrillar type chromoplasts, with particular emphasis on the morphogenesis and structural characteristics of the fibrils, was studied in Cucumis sativus petals by light and electron microscopies. Chromoplast differentiation was characterised by the progressive accumulation of fibrils which arranged in a parallel fashion, to form birefringent bundles. In the petals immediately before flower opening, the fibrillar bundles lost their compact structure and, at anthesis, the majority of them partially or completely disorganised. In the plastids of senescing petals, most fibrils were arranged in parallel again. Ultrastructural studies indicated that the formation of at least part of the fibrils started within plastoglobules. The outer diameter of most fibrils ranged from 13 to 18 nm. When transversely sectioned, they were polygonal in shape, often resembling pentagons or hexagons. In addition to these most common fibrils, different forms which appeared to be composed of two to several "incompletely separated" single fibrils were also frequently present. By using standard preparation methods, the coat of the fibrils did not appear as a uniformly stained layer, but consisted of darkly stained roundish subunits interposed by more lightly stained areas. The morphological observations are discussed with regard to the fine structural changes of chromoplasts during flower development, as well as to the structure of fibrils and the mechanisms of their formation.

chromoplast fibrils; chromoplast differentiation; ultrastructure; petals; Cucumis sativus

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