A NEW TYPE OF LIGHT ADAPTATION IN AQUATIC PLANTS

Based on the study of light dependence of photosynthesis in macroalgae adapted to a wide range of light intensities and on the determination of a system (set) of adaptive responses to decreased light intensities, the authors proposed a new type of light adaptation in aquatic plants-Ulva-type. In macroalgae of Ulva-type adaptation inhabiting shaded locations, the efficiency of utilization of low and high intensities of incidence light is increased, i.e. the initial slope of the photosynthesis-irradiance curve is steeper and the photosynthetic rate at light saturation increases. An increase in the efficiency of utilization of low intensities of incident light is due to an increased absorption of light and efficient utilization of absorbed light. The increase in the capacity of photosynthesis in shade-adapted specimens is achieved through an increase in the concentration of photosynthesizing units in the chloroplasts and in the activity of photosynthetic enzymes. The plants of Ulva-type adaptation are Ulva fenestrata, Grateloupia turuturu, Punctaria plantaginea, Sargassum pallidum and other species of macroalgae inhabiting a wide range of light environments.