The effects of light on sex determination in gametophytes of the fern <Emphasis Type="Italic">Ceratopteris richardii</Emphasis>

The sexuality of homosporous fern gametophytes is usually determined by antheridiogen, a pheromone that promotes maleness. In this work the effect of photomorphogenically active light on antheridiogen-induced male development was examined for gametophytes of Ceratopteris richardii. Although blue light did not affect sensitivity to Ceratopteris antheridiogen (A_Ce) in wild-type gametophytes, it was found that the gametophytes of the her1 mutant, which are insensitive to A_Ce, developed into males when grown under blue light in the presence of A_Ce. Thus, we conclude that another A_Ce-signal transduction pathway activated by blue light exists latently in the gametophytes of C. richardii. Red light, on the other hand, suppressed male development. Because simultaneous red and blue light-irradiation did not promote male development in the her1 gametophytes, the action of red light seems to dominate that of blue light. The results of experiments with a photomorphogenic mutant also suggested that phytochrome may be involved in the action of red light.