ULTRAVIOLET-B EFFECTS ON SPIRODELA-OLIGORRHIZA - INDUCTION OF DIFFERENT PROTECTION MECHANISMS

Ultraviolet-B (UV-B) tolerance in plants has mostly been correlated wi th the presence of screening pigments (e.g. flavonoids) or other reduc tions in leaf transmittance. We have exploited the rapid turnover of t he Photosystem II reaction center protein D1 as a sensitive in vivo pr obe for UV-B damage. We found that the aquatic monocot, Spirodela olig orrhiza, protects itself from UV-B irradiance using at least three dif ferent mechanisms. In one case, protection is correlated to the presen ce of UV-B screening pigments; in the second, an elevated oxygen-radic al detoxifying system parallels UV-B tolerance; while in a third, UV-B tolerance is related to a mechanism involving neither screening pigme nts nor increased radical scavenging capacity. This demonstrates that, in vivo, a plant can complement its UV-screening and attenuation stra tegies by other tactics as well.