The ultrastructure of proplastids in the leaves of five species of Orchids. I. Organization of the inner membrane system and divisions of the proplastids

Abstract

The ultrastructure of proplastids in the leaves of five species of orchids was investigated: Paphiopedilum, Stanhopea, Cymbidium, Coelogyne and Orchis. The proplastids of the different species differ in the density of their stroma. The most electron dense is the stroma of Paphiopedilum proplastids and the lowest electron-density is shown by Orchis proplastids. A characteristic feature of most of the investigated proplastids is the presence of prolamellar bodies. The frequency of their occurrence and their structure differ from species to species. The remaining membrane system is limited to single peripheral vesicles. Dividing forms of the proplastids have been observed. The number of dividing proplastids averages 5 per cent. The proplastids have been observed to divide by constriction, invagination of the inner membrane or arrangement of vesicles in the division plane.