Photosynthesis and photorespiration during the ontogeny of the bean plant

Ontogenetic changes in true photosynthesis, apparent photosynthesis, and photorespiration were measured in the individual leaves of bean plants throughout the development of the plant to flowering. The relationship between true photosynthesis and photorespiration (termed assimilation efficiency) was determined. Leaf resistances were also measured, and the relationships of photosynthesis and photorespiration to mesophyll resistance (r m ) and stomatal resistance (r s ) were determined.There is an intrinsic ontogenetic pattern of gas exchange for each leaf, but this is modified by events that take place during development in other parts of the plant such as subsequent leaf emergence or flowering. Photosynthesis and photorespiration appear to be affected by the requirement for export of assimilates, but the two processes vary independently. Photosynthesis is regulated by r m and is weakly regulated by r s as well. However, photorespiratory CO 2 release is not related either to r m or to r s under the conditions of these experiments. These results emphasize the importance of the precise control and description of experimental material in the analysis of gas exchange in leaves.