Differences in UV-B tolerance among Spirodela punctata ecotypes

Ultraviolet-B (UV-B) radiation negatively impacts on plant growth and development. Not all plants are UV sensitive: strong tolerance to UV-B radiation is particularly found among plants that naturally occur in areas of high UV-B radiation. There is limited knowledge about the mechanisms underlying such enhanced natural tolerance. In this study, we demonstrate strong differences in UV-B tolerance among Spirodela punctata ecotypes. Tolerance is visualized as sustained photosystem II (PSII) activity and biomass accumulation in fronds exposed to UV-B radiation. We find that the enhanced tolerance is constitutive and specific for UV-radiation stress, but it does not correlate with well-characterized UV-adaptation responses like the accumulation of bulk UV-screening pigments in the epidermis, or increased oxygen radical scavenging activity.