Abstract

Terrestrial microalgae evolved a variety of photoprotective strategies enabling a life on land. This includes the production of sunscreen compounds, which shield cells from excess radiation. Here, we report a new genus of conjugating green algae, Serritaenia gen. nov., whose members produce extracellular mucilage with a striking pigmentation. This phenomenon is very unusual for eukaryotic algae and poses cell biological and functional questions. So far, extracellular sunscreen pigments are exclusively known from cyanobacteria, while eukaryotic algae typically contain intracellular sunscreens. We demonstrate that pigmented mucilage in Serritaenia spp. can be induced by experimental exposure to UVB in an intensity-dependent manner, and that it strongly absorbs deleterious wavebands. Microscopic details of UVR-treated cells suggest that the directional secretion of pigmented mucilage is responsible for the defined and well-oriented pigment layers observed in natural material. Even though the chemical nature of the pigment remains to be elucidated, several pieces of evidence suggest that the ‘sunscreen mucilage’ of Serritaenia represents an elaborate photoprotective adaptation, unprecedented in eukaryotic algae.

摘要

陆地微藻进化出多种光保护策略，能够在陆地上生存。这包括生产防晒化合物，保护细胞免受过度辐射。在这里，我们报告了一种新的共轭绿藻属Serritaenia gen。nov.，其成员产生具有显着色素沉着的细胞外粘液。这种现象对于真核藻类来说是非常不寻常的，并提出了细胞生物学和功能问题。到目前为止，细胞外防晒色素仅来自蓝细菌，而真核藻类通常含有细胞内防晒剂。我们证明了Serritaenia中的色素粘液spp. 可以通过实验暴露于 UVB 以强度依赖性方式诱导，并且它强烈吸收有害波段。UVR 处理细胞的微观细节表明，色素粘液的定向分泌是在天然材料中观察到的明确且定向良好的色素层的原因。尽管色素的化学性质仍有待阐明，但有几项证据表明，Serritaenia的“防晒粘液”代表了一种精细的光保护适应，这在真核藻类中是前所未有的。