Induction of Conidium Formation in Neurospora by Lifting of Catabolite Repression

Abstract

I N T R O D U C T I O NIn a synthetic, liquid medium with ammonium instead of nitrate as nitrogen source and sucrose (2 yo) as the main carbon source, formation of macroconidia on the mycelial mat of Neurospora crassa is prevented (Turian, I 964). The anticonidial (repressive) effect of such a medium (M-medium) is reinforced by increasing the sucrose concentration but nullified by lowering it (Oulevey-Matikian & Turian, 1968). The same repressive effect is produced with glucose, and is accompanied by increased ethanol liberation through alcohol dehydrogenase (ADH) reductive activity (Turian, I 972). Acrylamide-gel electrophoresis of mycelial cultures of Neurospora crassa grown on the ammonium M-medium revealed only one wide alcohol-dehydrogenase band, but a second presumed to be an ADH with oxidative activity was detected in extracts of conidium-forming, nitrate-grown cultures (DelVecchio & Turian, 1968). A similar oxidative ADH was found by Zink (1969) to be synthesized in Neurospora grown on ethanol or in older, sugar-depleted cultures. This suggested a derepression effect which we have studied further in relation to the conidium-inducing effect of our low-sugar ammonium medium. Isocitrate lyase has been included for comparison with the oxidative activity of ADH because of its sensitivity to glucose or catabolite repression (Kornberg, 1959; Flavell & Woodward, 1970; Heick, 1971) and the common link of these enzyme activities with the acetate, conidiogenous metabolism (Turian, I 961 ; Turian & Bianchi, 1972). M E T H O D SNeurospora crassa (wild-type Lindegren A) was grown on modified Westergaard & Mitchell's media (1947), containing either nitrate and I O -~ M-potassium citrate to provide a conidiogenous medium, or I o -~ M-diammonium citrate replacing the above compounds to provide a myceliogenous medium. The standard 2.0% (w/v) sucrose content of these media was lowered to 0.2% (w/v) in half of the ammonium-containing cultures (Turian, For studies in enzyme activities, 250 ml Erlenmeyer flasks containing 50 ml liquid media were inoculated with 0.2 ml heavy conidial suspension and incubated for 60 h at 25 "C in partial darkness (short, daily light exposures to stimulate conidiation). The thick vegetative or thinner conidiated mycelia were harvested, washed with distilled water, dried between filter paper and disrupted with quartz sand in cold 0-1 M-tris-HCI buffer at pH 8.5. The homogenates were centrifuged at 10000 g for 20 min at o "C and the supernatants used in assays as alcohol-dehydrogenase(s) without any attempt to fractionate this total ADH into its isozymes. For the reductive assay of ADH, the reaction mixture consisted of: 0.

Metabolism of L-Threonine and its Relationship to Sclerotium Formation in Sclerotium rolfsii

“…Induction of conidium formation in Aspergillus (Smith & Galbraith, 1971) and Neurospora crassa (Turian, 1973) was related to increased activity of the glyoxylate cycle. p In the present study, it was found that L-threonine increased glyoxylate content of the mycelium, branching at the colony margins and formation of sclerotia in S. rolfii.…”

“…Sclerotium formation is probably inhibited by glucose due to its effect as a catabolic repressor (Lehninger, 1970;Turian, 1973).…”

Effect of Glucose, Ammonium and Media Maintenance on the Time of Conidiophore Initiation by Surface Colonies of Aspergillus nidulans

“…We now come back to the question of why surface colonies require a 24 h period of vegetative growth before initiating development. We have previously reported a gene-controlled activity which is necessary for the acquisition of competence to initiate development (Axelrod et al, 1973;Gealt & Axelrod, 1974). We suggest that the long time period of vegetative growth of surface colonies before initiation of development indicates the time required to complete this endogenous genecontrolled activity, and not that required to deplete exogenous nutrients.…”

vvd Is Required for Light Adaptation of Conidiation-Specific Genes of Neurospora crassa, but Not Circadian Conidiation

“…N. crassa can undergo sexual development leading to the production of ascospores and two forms of asexual reproduction leading to the formation of microconidia and macroconidia (Springer, 1993;Turian and Bianchi, 1972). Macroconidiation is induced by exposing vegetative hyphae to air or by starving for carbon or nitrogen (Turian, 1973;Turian and Bianchi, 1972). Conidiation is also regulated by the endogenous circadian clock (Pittendrigh et al, 1959;Sargent et al, 1966).…”