PHOTOSYNTHETIC UTILIZATION OF RADIANT ENERGY BY CAM DENDROBIUM FLOWERS

(CO2)-C-14 fixation was observed in orchid Dendrobium flowers; its rat e decreased with the flower development, Chlorophyll (Chl) fluorescenc e in different developmental stages of flowers was compared to other g reen plant parts (leaf, inflorescence stalk, and fruit capsule). The p hotochemical efficiency of photosystem 2 (PS2) (F-v/F-m) of a leaf was 14-21 % higher than that of a mature flower perianth (sepal, petal, a nd labellum) which had a much lower total Chl content and Chl a/b rati o. A higher quantum yield of PS2 (Phi(PS2)) than in the mature flowers was observed in all green parts. Flower sepals had higher Chl content , Chl a/b ratio, and F-v/F-m values than the petal and labellum. Durin g flower development the Chl content, Chl a/b ratio, F-v/F-m, and q(N) decreased while Phi(PS2) and q(P) remained constant. An exposure of d eveloping flowers to irradiances above 50 mu mol m(-2) s(-1) resulted in a very drastic drop of Phi(PS2) and q(P), and a coherent increase o f q(N) as compared to other green plant organs. A low saturation irrad iance (PFD of 100 mu mol m(-2) s(-1)) and the increase in q(N) in the flower indicate that irradiation stress may occur since there is no fu rther protection when the flower is exposed to irradiances above 100 m u mol m(-2) s(-1). A low Chl/carotenoid ratio in mature flower periant h as a consequence of Chl content reduction in the course of flower de velopment suggests a relief of irradiation stress via this mean.