The Fine Structure and Formation of Fibrils of Capsicum annuum L. Chromoplasts

Abstract

Summary The diameter of the fibrils of the chromoplasts of Capsicum annuum fruit varies between 12 and 148 nm, with maximum frequencies occurring at 12 nm intervals. Transverse and longitudinal sections are consistent with a microfibrillar fine structure of fibrils. Statistical analysis of measurement of microfibrils yields values of 12.1 nm for their diameter and 8.0 nm for their central, more electron translucent region. The microfibrils themselves may be composed of linearly aggregated subunits of protein. Fibrils are continuous through the plastoglobules which are associated with them, indicating that fibrils develop by the addition of material from the stroma. This may occur by the addition of concentric layers of microfibrils, or by further accumulation of microfibrillar subunits at the ends of the fibril in the stroma. This latter hypothesis is supported by the positive correlation between plastoglobule thickness and the diameter of the associated fibril, and by the uniform width of longitudinally sectioned fibrils.