Blue light‐induced acidification of the medium of a nitrate‐starved Chlorella mutant

Abstract

Irradiation with blue light resulted in acidification of the suspension medium of a colorless mutant of Chlorella kessleri (Fott et Novákóva, no. 9.80). Qualitatively red light gave the same result, although to a much lower extent than blue, whereas far‐red had little effect. A pulse of blue light led to a transient acidification of the medium. The light‐induced acidification was particularly pronounced if nitrate‐starved cells were used. Acidification was inhibited by vanadate (V2O5, Na3VO4), so that the phenomenon appears due to proton extrusion from the mutant. The light‐induced acidification was also observed in a yellow mutant and the wild‐type of Chlorella kessleri. The role of light in the acidification of the medium of algal cells is discussed in relation to the earlier findings that blue light enhances the uptake of nitrate in the colorless mutant; and that in Chlorella cells the transport process of nitrate is connected with a proton symport.