Action spectrum of phototaxis in a cryptomonad alga, Cryptomonas sp.

The action spectrum of the positive topo-phototaxis in Cryptomonaswas determined by photometry in the region of 400 to 680 nmat a stimulus intensity of 8.3 ? 10^–11 Einsteins cm^–2sec^–1. The action spectrum had a main peak at about 560nm unlike peaks for most other flagellated algae. Blue lightwas not very effective and red light above 640 nm had not effect. Swimming rates of individual organisms were measured by darkfield photomicrography. We concluded that the photokinetic effectwas negligible. Among the component pigments of this alga, phycoerythrin hadan absorption spectrum whose main peak appeared to coincidewith that of the phototactic action spectrum. (Received October 31, 1973; )