Sexual Hormones in Achlya

Abstract

The production of antheridial hyphae in heterothallic spp. of Achlya is initiated and controlled by 4 hormones comprising the A-complex. Hormones A and A2 are secreted by the veg. female mycelium and each alone can induce the response, whereas A1 and A3 are secreted by the male and neither can initiate the reaction. Hormone A induces the production of antheridial hyphae with an intensity which is a log. function of its concn. over a range from . 05 to 5000 U. /ml. The effect of A is enhanced by the presence of A1, the intensity of reaction being a linear function for subopt. concns. of A1 and increased by a factor of about 3 for opt. concns. of A1, Hormone A2 gives a reaction intensity which is roughly an exponential function of its concn. The augmentative effect of A1 on A2 is most pronounced with low concns. of A2 and diminishes with increasing concns. of A2. For combs. of A, A1 and A2, the reaction intensity is roughly a log. function of the concn. of A2 in the presence of A or in the combined presence of A and A1. At a concn. of 50 U. /ml. of A the effect of A2 on A and A1 is inhibitory. Hormone A3 limits the no. of antheridial hyphae produced by the plant, the inhibition being effective on the response induced by both A and A2 and on that induced by A in the presence of an opt. concn. of A1. The chemical identity of the hormones of the A-complex is unknown, although certain chem. and phys. properties of A and A1 have been descr. All are secreted by veg. plants, in the presence or absence of sexually compatible strains. The titers of A, A1 and A3 vary characteristically with the age of the cultures in which they are produced. A revised scheme for the hormonal mechanism in heterothallic Achlya spp. is presented, including all the members of the A-complex.