UV‐B INDUCTION OF UV‐B PROTECTION IN ULVA PERTUSA (CHLOROPHYTA)¹

Abstract

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 À 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 a,a-diphenyl-b-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.

Effects of nutrient supply on photosynthesis and pigmentation in Ulva lactuca (Chlorophyta): responses to short-term stress

“…The negative effect of increased temperature and UVB (Aguilera et al 2002) may be related to oxidative damage as reported in several algae by Lesser (1996). The involvement of UVB in the protection against UV light damage has already been reported in the brown macroalga Dictyota dichotoma (Flores-Moya et al 1999) and in the green alga Ulva pertusa (Han & Han 2005). Flores-Moya et al (1999) suggested that UVA radiation induces photoinhibition while UVB may be involved both in the impairment and in the recovery of photosynthesis.…”

Ultraviolet radiation shapes seaweed communities

“…Very recent studies demonstrated the solely UVB-induced increase in thallus absorption in Ulva pertusa with a maximum at 295 nm (Han and Han 2005), however, the responsible screening compound is still unidentified.…”

Acclimation of Red Sea macroalgae to solar radiation: photosynthesis and thallus absorptance

“…UVB under high PAR irradiance can even have beneficial effects on photobiological processes, e.g. in the brown alga Dictyota dichotoma (Flores-Moya et al 1999), in the green macroalga Ulva pertusa (Han & Han 2005) and in several shallow water tropical algae (Hanelt & Roleda 2009). Persistence of the inhibitory effect in the PAR+UVA treatment (absence of UVB) led Flores-Moya et al (1999) to suggest that UVA radiation exerts the main role in photoinhibition and UVB may be involved both in the impairment and the recovery of photosynthesis.…”