Chemosensory responses by the colorless inshore marine dinoflagellate Crypthecodinium cohnii were observed in quadrant-divided Petri plates containing an agar layer + liquid overlay. A suspension of organisms in salt solution was poured onto this and allowed to stand 3 hr. A differential tendency of the cells to become firmly attached or embedded in the substratum was observed when various substances were incorporated in the gel. A positive response (tendency to attach) occurred with: alpha-L-fucose, dimethyl-beta-propiothetin, betaine, sucrose, glycine, L-alanine, hemin, and fructose; negative response: formalin, glutathione, acid hydrolyzed agar, protamine SO(4), L-glutamic acid, lactose, glutamine, taurine, L-aspartic acid, putrescine 2 HCl, choline citrate, choline bitartrate, K citrate, and choline HCl. gamma-Aminobutyric acid was negative or positive depending on concentration. Dead or immotile cells did not become attached. The following compounds elicited no response: alpha-D-fucose, dimethyl acetothetin chloride, cyclic AMP, and glucose.
