ACCUMULATION OF PHOTOASSIMILATE BY PERONOSPORA-VICIAE (BERK) CASP ANDLEAVES OF PISUM-SATIVUM L - EVIDENCE FOR NUTRIENT-UPTAKE VIA INTERCELLULAR HYPHAE

Autoradiography showed that accumulation of label by hyphae of Peronos pora viciae (Berk.) Casp., in leaflets of Pisum sativum L. exposed to (CO2)-C-14, was up to 4.5 times greater in the susceptible cv. Krupp P elushka than the resistant cv. Early Onward. Concentrations of label w ere similar in apoplastic solutions from both cvs, although a greater volume was available in Early Onward. Uninfected Krupp Pelushka assimi lated more label from (CO2)-C-14 than Early Onward; para-chloro-mercur ibenzene sulphonic acid (PCMBS) treatment and infection reduced assimi lation by Krupp Pelushka but not Early Onward. Infected leaf tissue fr om Early Onward assimilated more label than Krupp Pelushka from [C-14] sucrose supplied to the apoplast. Transient treatment with PCMBS reduc ed assimilation of [C-14]sucrose into infected plant tissue to 30 and 61 % of untreated levels, in Early Onward and Krupp Pelushka respectiv ely. In contrast, autoradiography of hyphal fragments showed that the fungus accumulated 1.4 times more label from [C-14]sucrose than withou t PCMBS. The different nutrient status of leaves of Early Onward and K rupp Pelushka, and evidence that label from sucrose is accumulated by intercellular hyphae directly from the apoplast, are discussed in rela tion to the role of haustoria and mechanisms of compatibility.