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Pheromone-initiated sexual reproduction of Volvox carteri f. nagariensis is started by a “spontaneous” generation of sexual male spheroids at a rate of 10-4. As previously suggested, these males are mutants (sexc) which become independent of pheromone-controlled sex-induction. Unequivocal evidence for a mutative event now comes from the observation that the sexc trait is transmitted through cell lineages during embryogenesis, thus confirming earlier morphological analysis, Mutation semms to be restricted to cell division, The high frequency of mutation points to a special enchacing mechanism for whick the possibility of a genome rearrangement is discussed.

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The action of the macromolecular inducer glycoprotein on sexual reproduction in the green alga Volvox curteri can be modified by altering the external (intraspheroidal) CAMP concentration. Direct proof for the presence of CAMP in the spheroids is given. Protein binding assay and HPLC-fluorimetric analysis independently demonstrate the existence of CAMP in the matrix, cells, and culture medium. Its concentration is higher in sexual cultures, pointing to a transmitting function in sex induction. The presence in the matrix of other members of a protein phosphorylation system suggests an induction-specific signal cascade in this plant.