Reassimilation of carbon dioxide by Flaveria (Asteraceae) species representing different types of photosynthesis.

The capability to reassimilate CO2 originating from intracellular decarboxylating processes connected with the photorespiratory glycolate pathway and-or decarboxylation of C4 acids during C4 photosynthesis has been investigated with four species of the genus Flaveria (Asteraceae). The C3-C4 intermediate species F. pubescens and F. anomala reassimilated CO2 much more efficiently than the C3 species F. cronquistii and, with respect to this feature, behaved similarly to the C4 species F. trinervia. Therefore, under atmospheric conditions the intermediate species photorespired with rates only between 10-20% of that measured with F. cronquistii. At low oxygen concentrations (1,5%) the reassimilation potential of F. anomala approached that of F. trinervia and was distinct from that found with F. pubescens. The data are discussed with respect to a possible sequence of events during evolution of C4 photosynthesis. If compared with related data for C3-C4 intermediate species from other genera they support the hypothesis that, during evolution of C4 photosynthesis, an efficient capacity for CO2 reassimilation evolved prior to a CO2-concentrating mechanism.