UNVEILING NATURE'S SUNSCREEN: THE POTENTIAL ROLE OF LIVERWORT SCALES IN UV PROTECTION

UV radiation is important for plant life as it induces essential processes such as growth, germination, and secondary metabolite pathways. However, prolonged exposure to UV-A and UV-B radiation can have negative effects on organisms. For example, UV radiation can directly or indirectly damage DNA molecules and cause enzyme denaturation. Sessile organisms have multiple mechanisms, such as the evolution of various UV-absorbent pigments, that protect them from the negative effects of constant UV radiation exposure. While liverworts are a group of plants commonly associated with mesic and shaded environments, there are multiple species within this group that inhabit dry and sunlight-exposed environments. For example, the complex thalloid liverwort Calasterella californica (Hampe ex Austin) D.G.Long & T.X.Zheng lives in exposed outcrops across California, where it is exposed to a great amount of solar radiation. During the dry season, C. californica thalli dehydrate and become surrounded by their large purple ventral scales. The plants remain in this “dormant” state until the subsequent wet season, when the thalli rehydrate. Since the purple-red pigmentation in plants is often associated with light-damage protection, we hypothesize that the purple scales of xerophytic liverworts—like C. californica—protect the particularly vulnerable desiccated thalli from potential damage associated with UV radiation. As a first step to test this idea, we document the sunlight absorbance spectrum of the purple scales of C. californica and compare it to the more-common, translucent liverwort scales and to commercial sunscreen. We found that purple scales absorb UV radiation in a pattern that matches that of sunscreen, particularly for UV-A and UV-B radiation. Both sunscreen and purple liverwort scales absorb two to three times more UV-A radiation than translucent scales. These results are consistent with the idea that purple scales play a role in protecting dormant xeric liverworts against UV damage. Although we focused on the scales of C. californica, there are other liverwort species (like Reboulia hemisphaerica (L.) Raddi and Targionia hypophylla L.) that have similar purple scales and rolling mechanism; this points to a relatively widespread adaptive mechanism used by distantly related liverworts that could allow them to thrive in dry regions.