Effects of leaf age, basal meristem and infection with powdery mildew on photosynthesis in barley grown in 700 mu mol mol(-1) CO2

The rate of net photosynthesis in the second leaf of barley was higher in 700 than 350 mu mol mol(-1) CO2 when measured in the CO2 concentration in which the plants were grown, but the magnitude of this difference decreased as the leaf aged. Infection by powdery mildew accelerated the decline in net photosynthesis of leaves grown in either 350 or 700 mu mol mol(-1) CO2. A/C-i curves allowed the reduction in net photosynthesis of plants exposed to 700 mu mol mol(-1) CO2 or after infection by powdery mildew to be related to changes in the carboxylation efficiency or in the regeneration of ribulose 1,5-bisphosphate. The carboxylation efficiency declined in plants exposed to 700 mu mol mol(-1) CO2. In plants infected with powdery mildew, the reduction in net photosynthesis was associated with both reduced carboxylation efficiency and reduced ability to regenerate ribulose 1,5-bisphosphate. Reduced carboxylation efficiency of the second leaf of plants grown in 700 mu mol mol(-1) CO2 was not associated with a reduction in the concentration of rubisco within the leaf. In contrast to the presence of a close exogenous sink, leaf age had large effects on the acclimation of photosynthesis to 700 mu mol mol(-1) CO2.