Carbohydrate metabolism in source leaves of barley grown in 700 mu mol mol(-1) CO2 and infected with powdery mildew

Soluble carbohydrate accumulated faster in second leaf blades of barley when plants were grown in 700 mu mol mol(-1) CO2 rather than 350 mu mol mol(-1) CO2. Infection of the second leaf blade by powdery mildew had no effect on the concentration of soluble carbohydrate until 6 d after inoculation when it was lower than in controls. The accumulation of soluble carbohydrate in the second leaf of uninfected plants grown in 700 mu mol mol(-1) CO2 was due largely to earlier and faster accumulation of fructan. TLC showed that the series of fructan was not different in plants grown in 700 mu mol mu mol(-1) CO2 relative to plants grown in 350 mu mol mol(-1) CO2, neither did infection by powdery mildew affect the series of fructan present in the second leaf blade. The rate constant for phloem loading obtained by compartmental analysis of C-14 efflux from the leaf blade was not reduced in plants grown in 700 mu mol mol(-1) CO2, indicating that carbohydrate accumulation was not caused by reduced ability of the leaf to export carbon.