Ribulose Bisphosphate Carboxylase and Net CO₂ Fixation in Tomato Leaves

Abstract

The light-saturated rates of photosynthesis at 300 vpm CO₂ and 20°C (P_max) of leaves at different stages of development have been predicted with a knowledge of the amount and kinetics of tomato leaf RuBPc/o, based on the assumption that under these conditions the enzyme is fully activated and RuBP saturated. When grown in high CO₂ (1000 vpm) the amount and activity of RuBPc under unit surface area and P_max decreased sharply beyond about 25% of full leaf expansion compared with leaves grown in 300 vpm CO₂. When almost fully expanded the high CO₂ grown leaves contained only about half as much RuBPc as the leaves grown in a normal [CO₂] and P_max was similarly reduced. Overall, the predicted rates of P_max correlated reasonably well with observed rates, supporting the view that this enzyme may be a factor governing photosynthetic capacity.