Phototropic sensitivity in Vaucheria geminata regulated by 3',5'-cyclic AMP

Exogenous 3',5'-cyclic AMP in physiological concentrations inhibitsthe phototropic bending of Vaucheria geminata without affectinggrowth. Related substances known to change the intracellularcyclic AMP level also alter phototropic sensitivity. This indicatesthat the steering process (i.e., initial phototropic response)is separate from growth itself. Cyclic AMP extracted from this alga amounted to 0.2–0.3nmole per g fresh weight, or about 3 µM on a cytoplasmvolume basis. This value coincides with expected results fromexperiments with exogenous cyclic AMP. The results suggest thatendogenous cyclic AMP may play an essential role in the gain-controllingprocess of phototropism. ¹ Present address: Institute for Agricultural Research, TohokuUniversity, Sendai 980, Japan. (Received November 26, 1976; )