Subunits of Chloroplast Structure and Quantum Conversion in Photosynthesis

Abstract

Publisher Summary This chapter focuses on the subunits of chloroplast structure and quantum conversion in photosynthesis; and discusses some of the pertinent physiological observations on photosynthesis, the relationship of these physiological processes to structures seen with the light and electron microscopes, and the chemical, physical, and morphological properties of these structures. Studies of photosynthesis in green plants established the existence of light and dark reactions and predicted the occurrence of the photosynthetic unit. Combined cytological and biochemical studies have shown not only that the entire photosynthetic process is localized within the chloroplast but that the light and dark reactions and perhaps the photosynthetic unit may be assigned to ultrastructural features of the plastid. Of particular interest is the fact that the internal membrane system of the chloroplast appears to be built of subunits. The smallest of these is about 90 A. in diameter. These smallest subunits are seen in some preparations to form the quantasome (about 200 A. in diameter), and the quantasomes form the membrane. The definite assignment of photosynthetic unit function to the quantasome or perhaps quantasome aggregates awaits improved isolation techniques applied to chloroplast material of uniform morphology. The fact that chloroplast membrane surface morphology appears to be controlled by environmental conditions offers some intriguing developmental problems. Membrane function and efficiency in this system may eventually be correlated with membrane composition and structure. Application of freeze-etching to the study of these membranes has given a new insight into the morphology and possible distribution of photosynthetic substances within the membrane.