The submicroscopic development of chromoplasts in the fruit of Capsicum annuum L.

Abstract

From a structural point of view, there are three different types of chromoplasts in carotinoid pigmented plant organs (8): plastids which contain (1) microscopic crystals of carotinoids, (2) microscopic and submicroscopic yellow globuli, and (3) bundles of orange-red pigmented submicroscopic filaments. After having studied the development of the globuli in the second case (8), an investigation of the transformation of chloroplasts into the spindle-shaped chromoplasts containing submicroscopic filaments (23) has been undertaken. While the ultrastructure of the chloroplast, as well as that of the transformed chromoplast, are fairly stable and can be satisfactorily fixed, the stages of transition appear to be very unstable so that it is difficult to avoid swelling and artifacts even with osmic acid or permanganate. The filaments appear as bundles during and directly after the disintegration of the grana in the chloroplastic structure. But there is no direct transformation of the grana into the bundles of long filaments because only a few (3 or 4) such bundles are formed, while the grana are numerous (Fig. 2). Apart from their shape, the filaments display a similar ultrastructure to the grana discs in the active chloroplast because they show a denser osmophilic rind measuring 50 A in width and a less dense colorless core (Figs. 15 and 16). The origin and development of these filaments, which present some morphological resemblance to filamentous virus particles, is discussed.