ADAPTATIONS AT THE CELL AND ORGANELLE LEVEL FOR UTILIZING SUNLIGHT1-2

The discovery of multiple pathways of carbon dioxide assimilation and dissimilation in higher plants has drastically changed the research and thinking in plant biology. The theme is developed that adaptations within photosynthesis are of fundamental importance in plants and that changes in this dominant metabolic process arc apt to result in strong and immediate selection advantages in the course of plant evolution. Data are presented on the variations in photosynthetic CO2 assimilation in the reductive pentose phosphate cycle, the C4-dicarboxylic acid cycle, and in Crassulacean acid metabolism. Photo-synthetic studies with primitive plants such as P silo turn nudum indicate a metabolism similar to Cj-dicarboxylic acid may have arisen in this primitive plant. In order to establish a perspective on the metabolic processes in plants which might be subject to adaptation, we have considered the activities of major meta-bolic processes such as photosynthesis, photorespiration, dark respiration, transpira-tion, nitrogen fixation, ion uptake, and the synthesis of proteins, lipids, cell walls. Many of these metabolic activities are common to all of life forms and probabl