Morphogenesis in Mucor mucedo: mutations affecting gamone response and organ differentiation.

Mutants of Mucor mucedo minus strain that are affected in their trisporic acid (TA) mediated zygophore formation have been isolated. We have found mutants with cold sensitive (cs), with temperature sensitive (ts) and without zygophore formation as well as mutants with unstable zygophores (Zst-). From the appearence of certain pleiotropic phenotypes we deduce a one-dimensional sequence of states of competence of the mycelium to form different organs. TA appears to be a growth substance for zygophores acting on one transient state of competence. The fact that all isolates with lowered response to TA also have a lowered response to the mating type specific TA-precursor P strongly suggests that P has to be converted into TA before inducing zygophore growth. Furthermore, one mutant with lowered sensitivity to TA exhibits an excess zygophore formation in the presence of high TA-concentrations, while high concentrations of P cause a depressed zygophore formation (Fig. 6). Our interpretation of this behaviour is that P acts as an antagonist to TA in the regulation of zygophore growth.