The Interaction of the Chloroplast and the Cytosol

Abstract

Chloroplasts have been studied extensively. However, chloroplasts are only one type of plastid, and plastids of some type occur in all parts of a plant, where they perform a variety of functions. In tubers, for example, starch is stored in plastids called amyloplasts. In developing seeds, fatty acid synthesis takes place in colourless plastids called leucoplasts. In all plant tissues, the bulk of the biosynthetic activity of the cell occurs in the plastids. This means that there must be a continual exchange of metabolites between the cytosol and the plastids. However, this exchange must be tightly controlled. This is achieved by the inner membrane of the plastid being impermeable, even to small molecules , so that metabolities must be transported across the membrane by carriers. It is these carriers that control the flux of material into and out of the plastid.