Photosynthesis and Productivity Response to Changes in Blue/Red Light Ratio in Dunaliella Bardawil Under Field Conditions

Abstract

Light serves both as the energy source for photosynthesis and as an external regulating signal and it can be a limiting factor in photosynthetic productivity. To effectively utilize available light, plants and green algae can regulate leaf morphology, pigments composition, structure and function of thylakoid membranes and the overall rates of photosynthesis. These adaptation mechanisms can be induced by changes either in light intensity or quality, or both, and they appear to be highly conserved in all photosynthetic organisms examined (1). When the rate of photons absorption exceeds the rate of utilization of excitation energy, light utilization efficiency decreases and damage to the photochemical apparatus can occur. It can also result with regulated processes leading to the harmless dissipation of excess excitation energy. Among the radiationless dissipation mechanisms is the de-epoxidation of violaxanthin to form zeaxanthin molecule (the “xanthophyll cycle” (2)). Another protection mechanism is the accumulation of s-carotene in lipoidal globules in the interthylakoid space (3, 4), accompanied by the induction of Cbr synthesis (“Carotene biosynthesis related” protein, (5)), typical to the halotolerant green algae Dunaliella Bardawil.