Reversal of sexual induction in Volvox carteri by ultraviolet irradiation and removal of sexual pheromone

Washing in fresh culture medium or short exposure to ultraviolet irradiation (UV) was found to reverse the action of the sexual pheromone produced by the green alga Volvox carteri. Induced gonidia which would normally form egg-bearing females formed mainly asexual individuals in response to these treatments. The UV effect is strongly dependent on the stage of the life cycle at which exposure is given. Sexual induction in this organism requires early and continuous exposure to the sexual pheromone. The mechanism by which UV reverses sexual induction is not understood, but it could be caused by inactivation of the pheromone or by inactivation of a pheromone-induced repressor of asexual characters.