Oxine, Ferric Oxine and Copper Oxine as Inhibitors of Growth and Differentiation of Allomyces macrogynus

Abstract

Oxine is an inhibitor of growth and differentiation in A. macrogynus. Growth was inhibited by as little as 4 Jlg/ml and the first effect observed was inhibition of nucleic acid synthesis, followed by inhibition of protein synthesis. Consistent inhibition by oxine of the development of zoosporangia in starving plants required a concentration of 60 Jlg/m!. The degradation of RNA, always observed in starving plants, continued in the presence of oxine, showing that this is an independent phenomenon. When glucose was available, oxine increased the synthesis of trehalose without a comparable effect on glycogen synthesis. Cycloheximide increased trehalose synthesis to an even greater extent. The inhibition of glucose metabolism by oxine was concentration-and time-dependent. Oxine inhibition was reversible on transfer to nutrient solutions.Both iron oxine and copper oxine bind rapidly to the fungal walls. It is suggested that the site of binding is wall galactopeptide and that cell transport systems are disorganized. In the presence of glucose plants recovered from inhibition by ferric oxine without transfer. Observations are not in agreement with a theory that oxine inhibits transcription by chelating Mg and Mn.

Role of Glucose and Amino Acids in the Production of Resistant Sporangia by Allomyces macrogynus

“…It was originally suggested that trehalose might have a regulatory function because it was synthesized but not utilized by A. macrogynus. Increased synthesis of trehalose in the presence of oxine and of cycloheximide suggested that trehalose production was controlled by an unstable protein or the product of an unstable enzyme (Youatt 1982b). Results with trehalose synthesis by Dictyostelium discoideum suggest the possibility of a similar control process in that organism.…”

“…RNA degradation occurred whenever plants were transferred to starvation or semi-starvation conditions. RNA was still degraded when differentiation was inhibited by oxine (Youatt, 1982b). When glucose was added to plants which had been suspended in glutamate solution for 6•5 h, the development of resistant sporangia still occurred even though the RNA content had already reached its minimum concentration.…”

Amino Acids in the Control of Differentiation of Sporangia in Allomyces macrogynus

“…The total development of the zoosporangium is completed in 3 h and the involvement of stable mRNA for the whole process was easily demonstrated in the presence of actinomycin or oxine (Youatt 1982c). The maturation of resistant sporangia to the stage of spore release has not been described in less than 2 days (Machlis and Ossia 1953;Youatt 1973Youatt , 1980a.…”

Formation of O-Ethylhomoserine during the Controlled Production of Resistant Sporangia in Allomyces macrogynus

“…The prevention of this transcription by the supply of single amino acids requires rapid accumulation of the amino acid and is probably best explained by the enzymic production of ammonia at an appropriate site (Sandars and Youatt 1983). If glucose is available the trehalose-synthesizing enzymes are activated by amino acid deficiency and the trehalose content begins to rise even in the presence of cycloheximide (Youatt 1982b). One way of envisaging this activation is by protease action since amino acid deficiency does not prevent the maintenance of amino acid pools and protein turnover was demonstrated by Burke et al (1972) in similar conditions.…”

“…Trehalose accumulated to a higher concentration than in controls with glucose only-in one experiment to 98 J.Lg trehalose per milligram dry weight compared with 50 J.Lm/mg in the control. This was reminiscent of the effect of cycloheximide which also altered the maximum content of trehalose reached (Youatt 1982b).…”