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Abstract

The accumulation of phlorotannins after mechanical wounding and exposure to ultraviolet (UV) radiation was investigated in Laminaria hyperborea. Grazer action was simulated by mechanical wounding of the thalli with a cork borer, and investigated 0, 1, 2, 3, 5, 7 and 9 days after wounding. Simultaneously, the effects of exposure to photosynthetically active radiation (PAR) (25–30 µmol photons m−2 s−1) and additional UV radiation (7.5–8.8 W m−2 UV-A; 0.45−0.5 W m−2 UV-B) on the distribution of phlorotannins and structural changes were examined by light and fluorescence microscopy. Most phlorotannin-containing physodes were found in the outer cortex cells. However, some physodes were also present in the epidermis and in the medulla. Structural wound healing is divided into four stages: (1) gluing of the wound, (2) closing of the medullary cells to stop ‘bleeding’, (3) structural sealing of the medulla and enrichment of physodes in medullary cells and (4) cell divisions and re-differentiation of the cortex and medullary cells. The results suggest phlorotannins play a role in both wound sealing and reconstruction during wound healing. UV radiation has no effect on wound healing, but under both PAR and PAR with additional UV radiation an increase in the number of physodes is observed in the outer cortex and epidermal cells, indicating a reaction to high light stress. Overall, we show that phlorotannins play an important role during wound healing, and are inducible by PAR and PAR + UV radiation, indicating a function as photo-protective compounds.