The role of endosymbiotic algae in photoaccumulation of green Paramecium bursaria

The endosymbiotic unit of Paramecium bursaria with Chlorella sp. photoaccumulates in white, blue-green, and red light (<700 nm), whereas alga-free Paramecia never do. The intensity of photoaccumulation depends on both the light fluence rate and the size of the symbiotic algal population. Photoaccumulation can be stopped completely with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport. Hence the photosynthetic pigments of the algae act as receptors of the light stimulus for photomovement and a close connection must exist between photosynthesis of the algae and ciliary beating of the Paramecium.