THE ACTION OF 2-PERCENT, 21-PERCENT AND 100-PERCENT OF OXYGEN ON PRIMARY PHOTOCHEMISTRY OF PHOTOSYSTEM-II (PS-II), BIOSYNTHESIS OF PIGMENTSAND CARBON-DIOXIDE FIXATION BY ETIOLATED BEAN-LEAVES DURING GREENING

The responses of photosynthesis to oxygen concentration 2, 21 and 100% by etiolated bean leaves upon illumination were determined. After 0.3 , 3, 6, 10, 12 and 24 h of greening the following processes were measu red. (1) Functioning of PS II as reflected by changes in F-v/F-m ratio s and t(1/2) values. (2) Content and composition of pigments. (3) Capa city for carbon dioxide assimilation. The results showed that O-2 exer ts a complex inhibitory action on examined processes. The magnitudes o f inhibition increased with increasing of O-2 concentration and time o f its action. Under applied conditions the lag phase for development o f examined processes (with the exception of carotenoids) was in the ra nge 3-10 h. After 24 h of greening in 2, 21 and 100% of O-2 the F-v/F- m ratios attained values 0.55, 0.45, 0.13 respectively as compared wit h typical 0.80 of normal green leaves of bean. After 24 h of greening the inhibition by 100% O-2 as compared with zero inhibition by 2% O-2 were, in percentages: F-v/F-m, 78; t(1/2), 77; chlorophyll a, 59; chlo rophyll b, 69; beta-carotene, 78; neoxanthin, 60; zeaxanthin, 43; viol axanthin, 35; CO2 fixation, 95.