CHITIN DEACETYLASE ACTIVITY OF THE RUST UROMYCES-VICIAE-FABAE IS CONTROLLED BY FUNGAL MORPHOGENESIS

The broad bean rust fungus Uromyces viciae-fabae exhibits chitin only on surfaces of those infection structures which in nature are formed on the plant cuticle, but not on those differentiated in the intercellular space of the host leaf. Chitin deacetylase, an enzyme which converts chitin to chitosan, has been studied during in vitro differentiation of rust infection structures. Radiometric and gel electrophoretic analyses of crude extracts and extracellular washing fluids have shown that chitin deacetylase activity massively increases when the fungus starts to penetrate through the stomata, and that formation of the enzyme is strictly differentiation-specifically controlled. The extracellular portion of chitin deacetylase activity was about 53% in 24-h-old differentiated infection structures. Five isoforms with apparent molecular masses of 48.1, 30.7, 25.2, 15.2 and 12.7 kDa were detectable after substrate SDS-PAGE. The enzyme is temperature-sensitive and has a pH optimum of 5.5-6.0.