[On the enlargement of the contact area between chloroplasts and the cytoplasmic environment by formation of tubular protrusions of the plastid envelope]

Abstract

In the cells of yellow-green young leaves of the hybrid Oenothera (atrovirens x biennis) pingens · rubens with biennis plastids there are chloroplasts which possess tubuli extending from the outer limiting membrane into the cytoplasm. The tubuli have an average diameter of 40-50 nm; their length may reach at least 1 μm. They may branch and form a network. Occasionally they are in contact with the tonoplast, the plasmalemma, the endoplasmic reticulum or the dictyosomes. Series of adjacent sections show that membrane connections by such tubuli exist between chloroplasts and mitochondria or between different chloroplasts. Similar tubuli may also protrude from the inner limiting membrane of the chloroplasts into the plastid stroma. The possible function of the tubular chloroplast protrusions is discussed.