Sporogens, sterols, and sporulation of Leptosphaerulina briosiana

Abstract

The role of sporogenic compounds and sterols in the light-induced sporulation of Leptosphaerulina briosiana was investigated. Substances similar to P310 sporogens were extracted in greater amounts from light-grown L. briosiana than from dark-grown cultures. Sporulation was not induced in dark-grown L. briosiana treated with P310 substances extracted from light-grown L. briosiana or Ascochyta pisi. P310 substances in L. briosiana occurred primarily in dark-grown stromata or ascostromata from light-grown cultures. Ergosterol was present in L. briosiana, but ascospores were not produced by dark-grown L. briosiana treated with ergosterol or cholesterol. Sterol inhibitors delayed ascospore production and inhibited mycelial growth of L. briosiana. Autoclaved ergosterol counteracted the inhibitor; fatty acids, other sterols, and nonautoclaved ergosterol did not. Three sterol inhibitors prevented ascospore development in detached ascostromata. Neither P310 substances nor sterols could be substituted for the near-ultraviolet (near-UV) light required by L. briosiana for sporulation. P310 substances were more closely associated with stromatal formation than with spore differentiation and were fungal metabolites rather than photochemical degradation products. Near-UV light was required by L. briosiana for ascostromata maturation and ascospore differentiation rather than for ascostromata formation.