The photosynthetic capacity of pea leaves with a controlled chlorophyll formation

The relationship between chlorophyll content and photosynthesis as measured in whole leaves by CO2 uptake and by the component reactions of the electron transport chain of isolated chloroplasts, has been investigated. Leaves with a retarded chlorophyll formation, brought about by treatment with chloramphenicol, terramycin or by a low light intensity, were compared with control leaves (i) illuminated for a similar period of time, and (ii) with a similar chlorophyll content. There appeared to be no direct relationship between chlorophyll content and photosynthetic rate. It is suggested that CO2 uptake in low light treated leaves was limited by lack of enzymes, which are formed as a response to the supply of photosynthetic products. With terramycin and chloramphenicol the limiting factors may also be lowered enzyme levels, caused by specific protein synthesis inhibition. It is suggested that a component of Light System II required a high light intensity stimulation, and its formation was inhibited by chloramphenicol. The synthesis of a substance linking Light Systems I and II appears to be closely associated with chlorophyll formation, and could well be plastoquinone. Structural damage to the intermediate chain between Light Systems I and II is also apparently induced by chloramphenicol.