Studies in the Production of Auxins and other Growth Stimulating Substances by Exobasidium

Uppsala

1968

113 S.

43 Abb., zahlr. Lit. Ang.

Bandaufführung

113759

Using thin layer chromatography, investigations of the production of growth-stimulating substances by Exobasidium have been made on culture extracts of various species of the genus and on extracts of infected plant material. The biological effect of substances found in this way, and of known substances, has been measured in leaf and coleoptile tests. More detailed information about the identity of unknown substances has been obtained from spectrophotometric measurements. All the Exobasidium species studied could form indole compounds on media containing only an inorganic nitrogen source. However, production was considerably higher when organic nitrogen sources were present. Auxin metabolism on tryptophan medium was studied in special detail and the various steps in the reaction sequence have been followed up by incubation experiments with the various metabolites. In the same way, information as to which synthetic pathways are normal in Exobasidium has been obtained. Exobasidium forms two main indole compounds with high auxin activity, viz. indoleacetic acid (IAA) and IAA ethyl ester (IAEt). In extracts of Exobasidium-infected shoots, one main substance has been found, and this is very probably IAEt. In aerobic conditions the synthesis of IAA is mainly via indolepyruvie acid and indoleacetaldehyde, two labile compounds, which have, however been clearly shown. The synthetic pathway via tryptamine seems not to operate, but this does not prevent some Exobasidium species from being able to convert tryptamine to IAA easily. Formation of IAA via indolelactic acid has been shown to proceed very slowly. Quantitative calculations have yielded the result that the maximum amount of IAA can be up to 11.7 % of the added amount of DL-tryptophan in E. myrt. "Andr." 2, which is one of foresmost auxin producers. Distinct differences have been found in the ability of various Exobasidium species to form auxins. One group, mainly comprising species which infect the host plants systemically, forms large amounts of IAA rapidly, and, because the IAA oxidase effect is small, these are only slowly broken down to indolealdehyde and indolecarboxylie acid. Instead, IAA is converted to IAEt, which can be regarded as an easily utilized sotre of auxin. The second group, which comprises species which cause only small galls on the leaves, synthesizes IAA more slowly and the amounts are never so large, because breakdown is more effective here. Investigations of the ability of Exobasidium to form gibberellins and phenyllactic acid have shown that these are probably not formed. On the other hand, some kinetin-like substance may be produced, in any case by the two strains which cause witches' brooms on their hosts, as indicated by a certain amount of stimulation of callus growth with shoot formation, chlorophyll retention in leaves, root tests and UV-spectra.