Abstract
Photorespiration rates in tissue cultures of a C4 plant, Portulaca oleracea, were compared to those in tissue cultures of a C3 plant, Streptanthus tortuosus. The C4 plant tissue cultures have 1/2-1/3 the photorespiration rate of the C3 plant tissue cultures and respond to varying O2 concentrations in a manner typical of C4 plants. The lack of detectable photorespiration in C4 plants is probably not related to leaf anatomy.