Evidence for a light-dependent system for reassimilation of photorespiratory CO2, which does not include a C 4 cycle, in the C 3-C 4 intermediate species Moricandia arvensis.

Three methods of estimating photorespiratory rate in leaves of the C3-C4 intermediate species Moricandia arvensis and the related C3 species Moricandia moricandioides were compared. The results indicated that the photorespiratory rate in M. arvensis is less than in M. moricandioides, and that this is caused partly by reduced carbon flux through the photorespiratory pathway, and partly by the presence of a mechanism for enhanced photorespiratory CO2 reassimilation in the intermediate species. Measurements of the CO2 compensation point (Γ) in the two species supported this conclusion. A functional C4 pathway is unlikely to be involved in the reduction of photorespiratory rate in M. arvensis since pulse-chase experiments showed that carbon did not move from C4 acids to the reductive pentose-phosphate pathway in attached leaves under steady-state conditions at Γ.