CYTOKININ PRODUCTION BY 2 ECTOMYCORRHIZAL FUNGI IN LIQUID CULTURE

Radiommunoassays for zeatin riboside-type and iso-pentenyladenosine-type cytokinins are described. Each has a measuring range between ca 0.2 and 20 pmol of the riboside corresponding to the tritiated cytokinin riboside-dialcohol tracer, and is also sensitive to the corresponding free base, ribotide and 9-glucoside. Combined with HPLC, these two assays together provide a sensitive means for quantifying, and evidence contributing to the identification of, zeatin riboside- and iso-pentenyladenosine-type cytokinins in plant and fungal extracts. Culture filtrates of various mycorrhizal fungi were screened for cytokinin activity using the radioimmunoassays. The filtrates of two species, Thelephora terrestris and Laccaria bicolor, were further investigated using combined HPLC-RIA. While iso-pentenyladenosine was detected as the predominant cytokinin in culture filtrates of L. bicolor, zeatin, zeatin riboside iso-pentenyladenine and iso-pentenyladenosine were detected as the predominant cytokinins in culture filtrates of T. terrestris. The same cytokinins were also found in filtrates from these fungi grown in the presence of roots of the host species Picea abies. For T. terrestris, the production of zeatin riboside-type cytokinins was apparently enhanced by the presence of host roots. The occurrence of iso-pentenyladenosine in culture filtrates of L. bicolor and of both iso-pentenyladenosine and iso-pentenyladenine in culture filtrates of T. terrestris were confirmed by CI GC-MS.