Gorton Holly L, Vogelmann Thomas C
Department of Biology, St. Mary's College of Maryland, St. Mary's City, MD 20686-3001, USA.
Photochem Photobiol. 2003 Jun;77(6):608-15. doi: 10.1562/0031-8655(2003)077<0608:uratsa>2.0.co;2.
Aplanospores of Chlamydomonas nivalis are frequently found in high-altitude, persistent snowfields where they are photosynthetically active despite cold temperatures and high levels of visible and ultraviolet (UV) radiation. The goals of this work were to characterize the UV environment of the cells in the snow and to investigate the existence and localization of screening compounds that might prevent UV damage. UV irradiance decreased precipitously in snow, with UV radiation of wavelengths 280-315 nm and UV radiation of wavelengths 315-400 nm dropping to 50% of incident levels in the top 1 and 2 cm, respectively. Isolated cell walls exhibited UV absorbance, possibly by sporopollenin, but this absorbance was weak in images of broken or plasmolyzed cells observed through a UV microscope. The cells also contained UV-absorbing cytoplasmic compounds, with the extrachloroplastic carotenoid astaxanthin providing most of the screening. Additional screening compound(s) soluble in aqueous methanol with an absorption maximum at 335 nm played a minor role. Thus, cells are protected against potentially high levels of UV radiation by the snow itself when they live several centimeters beneath the surface, and they rely on cellular screening compounds, chiefly astaxanthin, when located near the surface where UV fluxes are high.
雪衣藻的不动孢子常见于高海拔的常年积雪地带，尽管温度很低且可见光和紫外线（UV）辐射水平很高，但它们在那里仍具有光合活性。这项工作的目的是描述雪中细胞的紫外线环境，并研究可能防止紫外线损伤的筛选化合物的存在和定位。紫外线辐照度在雪中急剧下降，波长为280 - 315 nm的紫外线辐射和波长为315 - 400 nm的紫外线辐射分别在顶部1厘米和2厘米处降至入射水平的50%。分离出的细胞壁表现出紫外线吸收能力，可能是通过孢粉素，但在通过紫外线显微镜观察到的破碎或质壁分离细胞的图像中，这种吸收很微弱。细胞还含有吸收紫外线的细胞质化合物，叶绿体以外的类胡萝卜素虾青素提供了大部分的筛选作用。另外在335 nm处有最大吸收峰的可溶于甲醇水溶液的筛选化合物起的作用较小。因此，当细胞生活在雪面以下几厘米处时，雪本身可保护它们免受潜在的高水平紫外线辐射；而当它们位于紫外线通量高的雪面附近时，则依赖细胞筛选化合物，主要是虾青素。
