Effect of Low Oxygen Partial Pressure during Growth on the Metabolism of Aspartic Acid and 3-Phosphoglyceric Acid in Leaves of the C4 Plant Amaranthus paniculatus

Summary Differences in carbon metabolism between leaves of Amaranthus paniculatus plants grown for 40 days in atmospheres containing 4% or 21% oxygen are observed in kinetic 14C2-feeding experiments on attached leaves during steady-state photosynthesis. Water-soluble leaf constituents were extracted from a defined area and the radioactivity and amount of certain metabolites measured. The basic difference was twice as much incorporation of 14C-radioactivity into the pool of aspartic acid after 15 min of 14CO2-fixation in 4% O2. This 14C-accumulation in the pool of aspartic acid was observed even after 2 min. After growth at low oxygen partial pressure the amount of aspartic acid and glycerate-3-phosphate (3-PGA) increases twofold. As judged on the base of relative specific activities (per cent of the feeding gas specific activity in dpm μg− 1 carbon) reached after 15 min of 14CO2-feeding nearly the total pool of aspartic acid is actively metabolised at both oxygen concentrations, whereas the entire amount of 3-PGA seems to be subdivided in at least two compartments differing largely in the turnover rates. The possible modes of the pool size changes of the two important metabolites as well as an “in vivo” inhibition of phosphoenolpyruvate carboxylase activity are discussed.