Polyol dehydrogenases in axenic mycelia of the wheat stem rust fungus Puccinia graminis f. sp. tritici

Abstract

Activities of the polyol dehydrogenases of Puccinia graminis f. sp. tritici were surveyed by measuring polyoldependent rates of reduction of NAD+ and NADP+ in cell-free extracts of axenically-grown mycelia. Seven of the eight polyols tested caused NADP+ reduction, with highest activity for D-glUcitOl, followed by L-arabitol, xylitol, erythritol, galactitol and ribitol, and low activity with D-arabitol; only D-mannitol failed to support activity. Inactivation rates were consistent with at least three separate enzymes, specific for D-ghcitol, xylitol and L-arabitol respectively, with apparent K, values of 170-198mM for xylitol and D-glUCitOl (K, for NADP+ 36-55 p~) ,and 34 mM for L-arabitol ( K , for NADP+ 1.2 p~) .The NADP+-dependent activities were almost completely inhibited by 2 mM-dithiothreitol, in contrast to the NAD+-dependent activities, which were stimulated. NAD+-dependent activity was highest with D-mannitol, followed by successively lower activities with D-arabitol, xylitol and D-ghcitol, with no activity with any of the other polyols; each of the four active polyols appeared to be oxidized by a different enzyme. All four NAD+-dependent activities were rapidly lost after Sephadex treatment of crude extracts.

Possible Roles for Mannitol and Mannitol Dehydrogenase in the Biotrophic Plant PathogenUromyces fabae

“…With regard to other rust fungi, a NAD 1 -dependent MTD activity was observed in axenic cultures of P. graminis f. sp. tritici (Maclean, 1990), whereas in spore extracts of Melampsora lini, a strong NADP 1 -dependent but only a minor NAD 1 -dependent MTD activity was found (Clancy and Coffey, 1980). The meaning of the differential cofactor specificity found in the different rust species remains to be elucidated.…”

“…Since mannitol-1-P dehydrogenase seems to be absent from Basidiomycetes (Hult et al, 1980), mannitol is most likely formed by direct reduction of Fru through a MTD (EC 1.1.1.67 or EC 1.1.1.138). Maclean (1990), for example, reported a NAD 1 -dependent MTD activity in Puccinia graminis f. sp. tritici axenic cultures, and Clancy and Coffey (1980) have shown NAD 1 -and NADP 1 -dependent MTD activity in Melampsora lini axenic cultures and uredospores.…”

Mannitol metabolism during pathogenic fungal–host interactions under stressed conditions

“…NAD + -dependent MTD activity is reported in P. graminis f. sp. tritici axenic cultures ( Maclean, 1990 ), and Clancy and Coffey (1980) have also shown NAD + - and NADP + - dependent MTD activity in Melampsora lini axenic cultures and uredospores ( Voegele et al, 2005 ).…”