INCREASE IN ENDOGENOUS AND EXOGENOUS CYCLIC-AMP LEVELS INHIBITS SCLEROTIAL DEVELOPMENT IN SCLEROTINIA-SCLEROTIORUM

Growth and development of a wild-type Sclerotinia sclerotiorum isolate were examined in the presence of various pharmacological compounds to investigate signal transduction pathways that influence the developme nt of sclerotia. Compounds known to increase endogenous cyclic AMP (cA MP) levels in other organisms by inhibiting phosphodiesterase activity (caffeine and 3-isobutyl-1-methyl xanthine) or by activating adenylat e cyclase (NaF) reduced or eliminated sclerotial development in S. scl erotiorum. Growth in the presence of 5 mM caffeine correlated with inc reased levels of endogenous cAMP in mycelia. In addition, incorporatio n of cAMP into the growth medium decreased or eliminated the productio n of sclerotia in a concentration-dependent manner and increased the a ccumulation of oxalic acid. Inhibition of sclerotial development was c AMP specific, as exogenous cyclic GMP, AMP, and ATP did not influence sclerotial development. Transfer of developing cultures to cAMP-contai ning medium at successive time points demonstrated that cAMP inhibits development prior to or during sclerotial initiation. Together, these results indicate that cAMP plays a role in the early transition betwee n mycelial growth and sclerotial development.