THE EFFECT OF ALBUGO-CANDIDA (WHITE BLISTER RUST) ON THE PHOTOSYNTHETIC AND CARBOHYDRATE-METABOLISM OF LEAVES OF ARABIDOPSIS-THALIANA

Albugo candida (pers.) O. Kuntze (white blister rust) is a biotrophic fungus which infects cruciferous plants including Arabidopsis thaliana (L) Heynh. We report the effect of this pathogen on the photosyntheti c and carbohydrate metabolism of A. thaliana. As infection progressed A. candida caused a reduction in the rate of photosynthesis when measu red at either ambient or saturating concentrations of CO2, These data suggested that both chlorophyll and Rubisco were lost from regions of infected leaves, and measurements of chlorophyll, Rubisco content and activity supported these observations, The reduction in the rate of ph otosynthesis was not caused by closure of stomata as transpiration was unaffected by the disease, Infected leaves accumulated both soluble c arbohydrates and starch, The activities of sucrose-phosphate synthase, sucrose synthase and ADP glucose pyrophosphorylase did not change in response to infection, However, the activities of both the wall-bound and soluble acid invertases were higher in infected leaves than in con trols; a new soluble invertase isoform with a pI of 5 . 1 appeared in infected leaves, The possible origin of the increase in wall-bound and soluble invertase activities and its effect on the carbohydrate and p hotosynthetic metabolism of the leaf are discussed.