Carbon Dioxide Assimilation by Leaves, Isolated Chloroplasts, and Ribulose Bisphosphate Carboxylase from Spinach

Abstract

The relationship between rate of photosynthesis and CO₂ concentration has been reinvestigated using isolated spinach (Spinacia oleracea) chloroplasts. The apparently low CO₂ concentration required for half-maximal photosynthesis is shown to result partly from a ceiling imposed by electron transport. In double reciprocal plots of rate against CO₂ concentration, this ceiling results in departures from linearity at high CO₂ concentrations. If these rate limitations are disregarded in extrapolation the “true” CO₂ concentration required for half maximal carboxylation by intact chloroplasts is approximately 46 μm (CO₂).