Carbon metabolism and gas exchange in leaves of Zea mays L.

Abstract

Changes in the rate of CO₂ uptake, chlorophyll a fluorescence and contents of metabolites were measured during illumination and darkening of maize leaves. Upon illumination, the contents of aspartate and alanine declined rapidly and there were rapid increases in the contents of 3-phosphoglycerate and triose phosphates. The amounts of pyruvate and phosphoenolpyruvate increased much more slowly. Upon darkening, the levels of 3-phosphoglycerate, phosphoenolpyruvate and triose phosphates fell sharply, while the amount of pyruvate increased. It is proposed that metabolite gradients in C₄ photosynthesis are built-up during induction through interchange of carbon between amino acids, metabolites of the C₄ pathway and 3-phosphoglycerate and triose phosphates, since CO₂ fixation during the first 5 min of photosynthesis was insufficient to account for the observed build-up of intermediates. Changes in the rates of CO₂ uptake and chlorophyll a fluorescence quenching are discussed in the light of the changes in metabolites.