Control of Chloroplast Structure by Light

Abstract

Publisher Summary This chapter focuses on certain of the striking similarities between physiological properties of chloroplasts and mitochondria. Special emphasis is given to the action of light on the control of chloroplast structure which includes such problems as light-dependent mechanisms for controlling the water and ion composition of chloroplasts from higher plants and algae. The elucidation of the light effect on the shape and volume of chloroplasts is complex because light induces not only size changes of chloroplasts, but also secondary reactions which can mask the occurrence of these phenomena within the cell. For example, illumination can initiate chloroplast movements in the cell perhaps by modifying the physical state of the surrounding protoplasm. In some instances, light has been found to induce a protoplasmic streaming which is strongly influenced by salts. Temperature, ions, and light, which affect protoplasmic viscosity can indirectly alter the volume of chloroplasts in vivo. The chapter also discusses the control of chloroplast structure in vitro and volume changes in chloroplasts and mitochondria. Chloroplasts and mitochondria show a remarkable resemblance to one another on a comparative physiological basis. Both possess an osmotic mechanism and two types of active mechanisms for promoting volume changes. Chloroplasts and mitochondria both appear to have an energy transfer pathway that seems capable of diverting energy generated by electron flow mechanisms into various modalities for work.