Induction of Phlorotannins During UV Exposure Mitigates Inhibition of Photosynthesis and DNA Damage in the Kelp Lessonia nigrescens

Phlorotannins of brown algae are multifunctional compounds with putative roles in herbivore deterrence, antioxidation and as primary cell wall components. Due to their peripheral localization and absorption at short wavelengths, a photoprotective role is suggested. We examined the induction of phlorotannins by artificial UV radiation in the intertidal kelp Lessonia nigrescens and whether they attenuate the inhibition of photosynthesis and DNA damage, two major detrimental effects of UV. The soluble and cell wall-bound fractions of phlorotannins were quantified in blades collected in summer and winter. Major findings were that (1) the synthesis of phlorotannins (both forms) was induced by UV only in summer; (2) the induction was fast (within 3 days); and (3) there was a positive relationship between of the contents of insoluble phlorotannins and the suppression of photoinhibition and DNA damage, measured as formation of cyclobutane pyrimidine dimers and 6-4 photoproducts. Overall, the photoprotective role of phlorotannins appears to respond to an interplay between the external UV stimulus, seasonal acclimation and intrinsic morpho-functional processes. In summer, when algae are naturally exposed to high UV irradiances, soluble phlorotannins are induced, while their transition to insoluble phlorotannins could be related with the growth requirements, as active blade elongation occurs during this season.