CHANGES OF THE DELAYED FLUORESCENCE CHARACTERISTICS IN SPIRULINA, ANABAENA AND CHLORELLA IN RESPONSE TO CHROMATIC ADAPTATION AND IRRADIANCE

Efficiency of the energy transformation for CO2 fixation (E), and kine tics of the initial O-2-mediated electron transport of Spirulina plate nsis (Gem.) Geitl, and Chlorella vulgaris Beijerinck cells were measur ed after adaptation to various growth irradiances (I) by means of the delayed fluorescence (DF) induction curves. Maxima of the membrane pot ential expenses during induction period were observed at I half satura ting oxygen evolution; they were shifted according to growth I remaini ng higher in Spirulina than in Chlorella. The alterations of absorbanc e and fluorescence spectra at 25 degrees C after adaptation to I demon strated changes in composition of pigments of algae, created to compen sate for the imbalance in radiation absorption between the two photosy stems. For Spirulina cells, the value of E was higher after growing un der low I, or under blue radiation absorbed mainly by photosystem (PS) 1 (400-500 nm) with excitation by yellow (570 nm) radiation. For Chlo rella cells, it was also higher after growing under low I. Under such conditions the half-rise time for DP-phase of DF induction curve decre ased, which reflected an acceleration of kinetics of the initial elect ron transport between photosystems. An opposite situation was observed with Spirulina cells grown under high I or yellow radiation, and Chlo rella cells from high I. Enhancement of effective PS2/PS1 ratio associ ated with decrease of reaction centre (RC) 2/RC1 stoichiometry may be a cause of the increase of E and high membrane energization under satu rating I in algae adapted to low I.