Control of photorespiration at RuBP carboxylase/oxygenase level in ryegrass cultivars

Abstract

PHOTORESPIRATION is probably a key intrinsic factor limiting photosynthetic productivity in C₃ plants. Attempts to control photorespiration with inhibitors of the metabolism of various photorespiratory intermediates have yielded unsatisfactory results with whole plants. A logical endogenous control point would be the branch point between photosynthetic and photorespiratory pathways, as most if not all the substrate for photorespiration is formed by the oxygenase function of ribulose bisphosphate carboxylase (RuBP carboxylase). There is considerable direct and indirect evidence suggesting that the oxygenase and carboxylase functions of this enzyme are tightly linked^1,2. However, temperature has been shown to have differential effects on the affinities of soybean RuBP carboxylase for CO₂ and O₂ (ref. 3), and mutant strains of Chlamydomonas and tobacco with altered carboxylase/oxygenase affinities have also been reported^4,5. We present here evidence for genetically controlled variation in the relative affinities of the RuBP carboxylase from ryegrass for CO₂ and O₂.