Control of Sexual Development in Gametophytes of Ceratopteris richardii: Antheridiogen and Abscisic Acid

The species-specific chemical messenger, antheridiogen, mediates the differentiation of male gametophytes in the fern Ceratopteris richardii Brongn. For different genetic strains, characteristic frequencies of sexual gametophytes primarily depend upon the relative sensitivity of gametophytes to antheridiogen. Exogenous supplementation with abscisic acid inhibits this antheridiogen response in sensitive strains of C. richardii. To further clarify the basis of the antheridiogen sensitivity, we examined the responses of gametophytes to antheridiogen and abscisic acid in three strains with distinct sensitivities to these agents. Depending upon strain and sexual phenotype, abscisic acid inhibited male morphology, inhibited antheridia production, and reduced gametophytic growth. An inverse relationship of antheridiogen and abscisic acid sensitivity indicated that endogenous levels of abscisic acid may contribute to the antheridiogen sensitivity of individual gametophytes. Even though abscisic acid contents of spores and young gametophytes did not correspond to the relative sensitivities of strains to antheridiogen, concentrations in mature spores and sexually indeterminate gametophytes were sufficient to contribute substantially to a constraint of antheridiogen responses.