Abstract
The oxygen consumption of a starved chlorophyll-free, yellow mutant of Chlorella vulgaris is enhanced by very small amounts of blue light ([lambda] 450 m[mu]); a saturation level is reached at about 500 ergs cm-2 sec-1. At that intensity the respiration is about 3 times greater than in the dark. An action spectrum for the enhancement of respiration shows 2 peaks around A 450 and 375 mu. Flavins and cis-carotenoids are discussed as the pigments involved.