Wound plug chemistry and morphology of two species of Caulerpa – a comparative Raman microscopy study

Caulerpa spp. form a polymer wound plug that seals their giant cells after mechanical injury to prevent fatal loss of cell material. First insights into the chemical processes underlying this rapid biopolymer formation were obtained by biochemical and analytical methods including mass spectrometry and Raman spectroscopy. Here we introduce a comparative Raman spectroscopic study of the wound plug formation in the invasive Caulerpa taxifolia (Valh) Agardh, 1817 and the non-invasive Caulerpa prolifera J.V. Lamour. In both species the enzymatic transformation of the main secondary metabolite caulerpenyne plays a key role in the formation of the wound plug. At the inner border of the wound plugs an accumulation of caulerpenyne is observed. Furthermore, caulerpenyne and products resulting from its enzymatic transformation and co-polymerization with proteins are found within the wound plug. However, both species possess significant differences in the chemistry of their wound plugs. The Raman spectra reveal a separation of the wound plug of C. taxifolia into two chemically distinguishable zones, while the wound plug of C. prolifera consists of only one chemically homogeneous zone. These results can explain differences in the morphology of the wound plug in both species.