The Phase Structure of Galactolipids and Their Role in the Formation of the Prolamellar Body

Abstract

In leaves of dark grown plants, proplastids differentiate to etioplasts. In this plastid, two different membrane systems are formed, the normal planar prothylakoid (PT) membrane and the regulary branched crystalline prolamellar body (PLB) membrane (Fig. 1). Despite beeing heterogenous in structure these membranes are continuous. The structure of the PLB membrane has been extensively studied by electron microscopy, for summaries see 1 and 2. The PLB membrane is a unit membrane (3) where the crystalline lattice is formed by 4- or 6-armed units (Fig. 2). The 4-armed unit is a tetrapod where 4 tubes meet in one point with equal angles. Tetrapods are arranged in different networks analogous to the crystal structures in wurtzite and zincblende (= diamond). The PLB can be formed by either the wurtzite or the zincblende type or by a combination of the two types in one PLB. The 6-armed unit is a cubic structure where the 6 tubes meet at right angles.