Anoxia induces increased activity of alternative oxidase in fungus Phycomyces blakesleeanus

Abstract

Alongside classical, cytochrome respiratory pathway, Phycomyces blakesleeanus possess alternative, cyanideresistant respiration (CRR) facilitated by alternative oxidase (AOX). In order to study role of oxygen in regulation of CRR, the effects of cyanide on respiration of 24h old mycelia in aerated (control), hypoxic and anoxic conditions were measured. Mycelium was incubated in these conditions for 1.5h, 3h and 5h. After 1.5h, AOX activity was increased only in specimens incubated in anoxic conditions (13.6%). After 3h, increase in AOX activity was significant in both hypoxic and anoxic specimens (18.9% and 18.8%, respectively), with even greater increase after 5h, 20.7% for hypoxic and 23.3% for specimens in anoxic conditions. Mycelia treated for 5h was then oxygenated for 10 minutes. This induced decrease in AOX activity of 17% in anoxic and even 23.9% in hypoxic mycelia. AOX is recognized as one of the mechanisms for maintaining low levels of reduced ubiquione which can function in conditions in which cytochrome chain is disabled, such as anoxia. This is in concordance with results obtained on P. blakesleeanus, where AOX levels rise in hypoxic and anoxic conditions and decrease close to control level shortly after introduction of oxygen into the system.