REACTIVATION OF PHOTOSYNTHESIS IN THE PHOTOINHIBITED GREEN-ALGA CHLAMYDOMONAS-REINHARDTII - ROLE OF DARK RESPIRATION AND OF LIGHT

Effect of quality, quantity and minimum duration of light on the proce ss of recovery was investigated in the photoinhibited cells of the gre en alga Chlamydomonas reinhardtii. Complete and rapid reactivation of photosynthesis took place in diffuse white light of 25 mu mol m(-2) s( -1). The recovery was partial (< 10%) in the dark. Far red (725 nm), r ed (660 nm) and blue light (480 nm) in the range of LC) to 75 mu mol m (-2) s(-1) did not enhance the process of reactivation. Photoinhibited cells incubated in dark for 15 min when exposed for 5 min to diffuse light (25 mu mol m(-2) s(-1)) showed complete reactivation. Even expos ure of 15 min dark incubated photoinhibited cells to photoinhibitory l ight (2500 mu mol m(-2) s(-1)) for 5 s fully regained the photosynthes is. The study indicated a very precise and triggering effect of light in the process of reactivation. The dark respiratory inhibitor KCN and uncouplers FCCP and CCCP increased the susceptibility of C. reinhardt ii to photoinhibition and also prevented photoinhibited cells to react ivate fully even after longer period of incubation under suitable reac tivating conditions. Of the various possibilities envisaged to assign the role of dark respiration in recovery process, supply of ATP by mit ochondrial respiration appeared sound and pertinent.