Roseoflavin inhibition of photoconidiation in a Trichoderma riboflavin auxotroph: indirect evidence for flavin requirement for photoreactions.

Abstract

AbstractRoseoflavin, an analog known to compete with riboflavin in Lactobacillus casei, riboflavin‐deficient rats, and fungi, was used to ascertain whether a flavin plays a role as a sensitizing pigment for photomorphogenesis in the fungus Trichoderma. Roseoflavin inhibited blue light induced conidiation of a riboflavin‐requiring auxotroph of Trichoderma. Colonies pre‐incubated with roseoflavin needed six times more light to saturate conidiation. Roseoflavin did not change the dark rate of conidial development indicating that it interfered only with the photoact. A revertant from the riboflavin auxotroph strain was not inhibited by roseoflavin. Simultaneous addition of 10 μM riboflavin prevented inhibition by 6.4 μM roseoflavin. Thus, roseoflavin inhibition is probably specific, possibly replacing riboflavin or one of its metabolites in the light reactions. There was no detectable shift in the action spectrum towards the green where roseoflavin absorbs; thus it did not replace a flavin as an efficient photoreceptor.