Sporulation and peroxidase in Bipolaris maydis: effects of xylose and thiamine

Sporulation of the fungus Bipolaris maydis increased and peroxidase (EC 1.11.1.7) activity decreased when xylose was added as a supplement to a basal glucose – mineral salts – agar medium containing either L-asparagine or NaNO3. With L-asparagine, thiamine–HCl (1.0 mg/ℓ) caused a significant decrease in sporulation and an increase in peroxidase activity. The magnitude of the decrease induced by thiamine–HCl in sporulation and increase in residue peroxidase activity appeared greater on a non-supplemented medium than on one supplemented with xylose. With NaNO3, the magnitude of the decrease in sporulation induced by 0.1 mg/ℓ thiamine–HCl appeared comparable whether or not the medium was supplemented with xylose, but the magnitude of the increase in residue peroxidase activity was greater without than with xylose. Quantitative determination of intracellular phenols as possible substrates for peroxidase revealed that there was no change in total phenol concentration regardless of the xylose and thiamine–HCl content of the media. The apparent inverse relationship between sporulation and peroxidase activity in B. maydis provides clues to the specific regulatory mechanisms involved in sporulation.