Development of Chloroplasts Structure and Function

Abstract

As a developmental system, the chloroplast has several exceptional features. First, its developmental path spans a wide structural range, from the extremely primitive to the complex. During the process, a large amount of the eventual major membrane system in the plant cell is produced. Thus, the morphological changes are striking and are readily described by electron microscopy. Second, several biochemical changes are equally as impressive as the structural changes. Extensive synthesis of lipids, including chlorophyll, is required for formation of the membrane. Proteins that become integrated into the growing membrane are synthesized both inside and outside the organelle. And photosynthetic activities develop in parallel with the structural changes. As described in Chapter 3, chloroplasts and thylakoid membranes are relatively easy to purify, which makes possible careful biochemical analysis. Third, a feature that has attracted numerous investigators is that both the nuclear-cytoplasmic and chloroplastic systems of genetic expression in plant cells are involved in this developmental process. Key questions that have been examined refer to the role of each genetic system and where each component of the chloroplast is synthesized. Chloroplast and cytoplasmic ribosomes are structurally different and can be specifically inhibited to examine the source of a protein. Confirmation that a protein is made inside the chloroplast can be obtained by examining products synthesized by the isolated organelle.