14CO2fixation in leaf discs ofPhaseolus vulgaris

摘要

Leaf discs ofPhaseolus vulgarisL. were exposed to14CO2in light, and transient changes in the radioactivity of photosynthetic intermediates were determined when illumination was interrupted or the CO2concentration lowered. The responses of phosphoglyceric acid, hexose monophosphate, and ribulose diphosphate showed that the Calvin cycle operates in this tissue. Turning off the light caused a rapid drop in14C-sucrose and in the total14C-content of the tissue, with a simultaneous rise in radioactive alanine, glutamate, malate, and aspartate, suggesting the rapid entry of sucrose carbon into respiratory pathways. Lowering the CO2concentration resulted in a transient rise in14C-glycolate which was followed by a temporary increase in14C-serine-glycine and in the ambient CO2concentration. This supports the hypothesis that glycolate produced in photosynthesis is a substrate for glycine and serine synthesis as well as for CO2evolution.