Association of Rhizomorph Formation with Laccase Activity in Armillaria spp.

Abstract

2527Ethanol and other substances that induce rhizomorphs in Armillaria spp. also induced laccase formation. In a range of isolates rhizomorph production and laccase activities were positively correlated. Laccase was first detectable just before the appearance of rhizomorph initials. Its activity reached a peak when rhizomorph growth rate was highest and fell to near zero when rhizomorph growth ceased. Laccase was not detected in non-induced cultures. Laccase reaction with chromogenic substrates was much higher in rhizomorphs than in mycelia. Laccase activity and rhizomorph production, but not mycelial growth, were decreased in the presence of enzyme inhibitors with activity against laccase. The results suggest a role for laccase in morphogenesis and/or growth of rhizomorphs.

Purification of laccase I from Armillaria mellea

“…The method was as described previously (Pacy & Thurston, 1987 Accumulation of laccase activity in the medium of A . rnellea cultures Appearance of laccase activity in the medium of A. mellea cultures correlates with synthesis of rhizomorphs (Worrell et al, 1986). In a series of preliminary experiments, it was established that higher levels of laccase activity were obtained in malt extract medium than in the defined medium employed by Worrell et al (1986) and that shallow layers of liquid medium that allowed the relatively rapid development of aerial mycelium gave higher levels of laccase activity (and rhizomorph dry weight).…”

“…It is clear that the initiation of both processes requires the development of aerial mycelium, is favoured by high oxygen tension and is not affected by C 0 2 tension (Worrell, et al, 1986). Under continuing high oxygen tension, however, laccase activity rapidly declines after reaching a maximum (Fig.…”

“…2) and the cultures develop extensive dark pigmentation, presumably as a result of laccase action (not shown; cf. Worrell et al, 1986). If oxygen availability is limited (by sealing culture vessels after inoculation), not only is more laccase recovered (Fig.…”

“…In contrast, other basiodiomycetes such as Lentinus edodes and Schizophyllum commune secrete laccase in association with fruit body development (Leatham & Stahmann, 1981;De Vries et al, 1986). Armillaria mellea secretes laccase activity in association with the differentiation of vegetative mycelium to form rhizomorphs (Worrell et al, 1986). Although not all Armillaria spp.…”

Diphenol Oxidases, Enzyme-catalysed Browning and Plant Disease Resistance

“…Laccase production by B. cinerea was reported to be induced, first by a phenolic substance and secondly by the products of pectin degradation (Marbach etal., 1985); thus it was induced during cell wall degradation following successful infection. Laccase has also been implicated in rhizomorph (Worral et al, 1986) and appresorial (Kubo etal., 1982(Kubo etal., , 1983 formation. The melanins thus produced have been reported to play an important role in disease development including protection of the hyphae from cell-wall degrading enzymes (De Cal and Melgarejo, 1994).…”