UV-B induction of UV-B protection in Ulva pertusa (Chlorophyta)

The green macroalga Ulva pertusa Kjellman produced UV-B absorbing compounds with a prominent absorption maximum at 294 nm in response only to UV-B, and the amounts induced were proportional to the UV-B doses. Under a 12:12-h light:dark regime, the production of UV-absorbing compounds occurred only during the exposure periods with little turnover in the dark. There was significant reduction in growth in parallel with the production of UV-B absorbing compounds. The polychromatic action spectrum for the induction of UV-B absorbing compounds in U. pertusa exhibits a major peak at 292 nm with a smaller peak at 311.5 nm. No significant induction was detected above 354.5 nm, and radiation below 285 nm caused significant reduction in the levels of UV-B absorbing compounds. After UV-B irradiation at 1.0 W.m(-2) for 9 h, the optimal photosynthetic quantum yield of the samples with UV-B absorbing compounds slightly increased relative to the initial value, whereas that of thalli lacking the compounds declined to 30%-34% of the initial followed by subsequent recovery in dim light of up to 84%-85% of the initial value. There was a positive and significant relationship between the amount of UV-B absorbing compounds with antioxidant activity as determined by the alpha,alpha-diphenyl-beta-picrylhydrazyl scavenging assay. In addition to mat-forming characteristics and light-driven photorepair, the existence and antioxidant capacity of UV-B absorbing compounds may confer U. pertusa a greater selective advantage over other macroalgae, thereby enabling them to thrive in the presence of intense UV-B radiation.