Phototaxis in Cryptomonas sp. under condition suppressing photosynthesis

Abstract

Effects of 3-(3, 4-dichlorophenyl)-l, 1-dimethylurea (DCMU) on photosynthetic oxygen evolution, respiratory oxygen uptake, phototactic response and swimming rate in Cryptomonas sp. were determined and compared. Photosynthetic oxygen evolution was completely inhibited in the presence of 10⁻⁵M DCMU. The treatment did not significantly affect the rates of respiratory oxygen uptake, phototaxis, and swimming, indicating that direct participation of photosynthesis in the phototaxis of this alga can be ruled out. Wavelength dependency of photosynthetic oxygen evolution was also determined in the range of 560 to 700 nm. The rate of photosynthetic oxygen evolution at 680 nm was as high as that at 560 nm, but no phototactic activity was seen at 680 nm although it was maximum at 560 nm. This is consistent with the above conclusion.