Photoinhibition of Photosynthesis and in Vivo Chlorophyll Fluorescence in the Green Alga Ankistrodesmus braunii

The unicellular, green alga Ankistrodesmus braunii is subject to a rapid photoinhibition of photosynthesis when exposed to a photon fluence rate in excess of that required to saturate photosynthesis. Photoinhibition is manifested as a time-dependent decrease in the capacity for either 14CC>2 fixation or CO2-dependent O2 evolution. Room temperature chlorophyll fluorescence induction in intact cells, has been used to probe the primary site(s) of light damage during photoinhibition. Initially, at least, photo-inhibition is due to a block in Photosystem II of photosynthetic electron transport, at a site on the water-splitting side