DNA-containing Regions in Various Plastid Types

Abstract

Summary The fine structure of various plastid types in relation to the localization of starch granules and lipid droplets was studied. In leucoplasts of Cucumis cotyledons as well as in leaf chloroplasts of the various plant species ( Pisum, Aspidistra, Billbergia, Raphanus, Paphiopedilum, Stanhopea and Clivia ) the starch granules were found to be in close contact with DNA in the electron-transparent regions of the plastid matrix. Various stages of the formation of starch granules can be followed in chloroplasts. Lipid droplets in the leaf chloroplasts of Stanhopea and Clivia , which are reserve substance like starch grains, are also localized in the DNA-containing electron-transparent areas of the chloroplast matrix. In this case also different stages of the formation of lipid droplets can be seen. The association of starch granules and lipid droplets with DNA-fibres was so often observed, that it probably reflects causal correlation. It is very likely that plastid DNA plays a role in the formation of reserve substances in these organelles of the plant cell. The fine structure of the DNA-containing electron-transparent areas in plastids of etiolated Cucumis cotyledons as well as in chloroplasts of several plant species belonging to mono- and dicotyledons was described. The plastids of Stanhopea and Clivia leaves were studied in the course of the differentiation to fully organized chloroplasts. The ultrastructure of the DNA-containing regions in the matrix of chromoplasts of detached Cucumis cotyledons treated with a growth retardant is also described.