A STAGE-SPECIFIC BLOCK IS PRODUCED IN CARROT SOMATIC EMBRYOS BY 1,2-BENZISOXAZOLE-3-ACETIC ACID

1,2-Benz-isoxazol-3-acetic acid is slightly toxic to unorganized growi ng carrot cells and completely prevents somatic embryogenesis beyond t he globular stage. Its action is time dependent: if added early, it af fects the determination of the early stages; if added later, after det ermination has occurred, it has practically no effect. The blocked for ms can evolve, in the presence of the compound, creating secondary emb ryos that, in turn, are arrested at the globular stage. Since the seco ndary embryos adhere to the primary ones, irregular polyembryonic mass es of typical appearance are created. The internal structures of the b locked globular embryos were examined and were shown to be enlarged, v acuolized and detached from the central cells. The protoderm also disp layed an altered appearance. These data, when considered together with the effects of the compound on rooting and callus formation, suggest that benz-isoxazol acetic acid acts as a weak auxin.