Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, As, Norway.
Planta. 2010 Apr;231(5):1003-11. doi: 10.1007/s00425-010-1103-3. Epub 2010 Feb 5.
Lichens, representing mutualistic symbioses between photobionts and mycobionts, often accumulate high concentrations of secondary compounds synthesized by the fungal partner. Light screening is one function for cortical compounds being deposited as crystals outside fungal hyphae. These compounds can non-destructively be extracted by 100% acetone from air-dry living thalli. Extraction of atranorin from Physcia aipolia changed the lichen colour from pale grey to green in the hydrated state, whereas acetone-rinsed and control thalli were all pale grey when dry. Removal of parietin from Xanthoria parietina changed the colour of desiccated thalli from orange to grey. Colour changes were quantified by reflectance measurements. By a new chlorophyll fluorescence method, screening was assessed as the decrease in incident irradiance (PAR) necessary to reach identical effective quantum yields of PSII (Phi(PSII)) in acetone-rinsed and control thalli. Thereby, we estimated a screening efficiency due to cortical atranorin crystals at 61, 38, and 40% of blue, green and red light, respectively, whereas parietin screened 81, 27 and 1% of these wavelength ranges. Removal of atranorin caused similar levels of increased photoinhibition for P. aipolia in blue, green and red light, whereas parietin-deficient thalli of X. parietina exhibited increased photoinhibition with decreasing wavelengths. Atranorin possibly prevents water from entering the spaces between the hyphae in the cortex. The air-filled cavities with white atranorin crystals reflect excess light, whereas the yellow compound parietin absorbs excess light. Thereby, both atranorin and parietin play significant photoprotective roles for symbiotic green algae, but with compound-specific screening mechanisms.
地衣是藻类和真菌共生体，常积累大量由真菌合成的次生化合物。皮层化合物作为晶体沉积在真菌菌丝外，起到光屏蔽作用。这些化合物可以用 100%丙酮从风干的活体地衣中无损提取。从石黄衣 Physcia aipolia 中提取的无羁萜使地衣在水合状态下的颜色从浅灰色变为绿色，而用丙酮冲洗过和对照的地衣在干燥时均为浅灰色。从石黄皮 Xanthoria parietina 中去除石耳素会使干燥的地衣颜色从橙色变为灰色。通过反射率测量来量化颜色变化。通过一种新的叶绿素荧光方法，评估了以到达相同有效 PSII 量子产量（Phi(PSII)）所需的入射光（PAR）减少来评估屏蔽，即分别为 61%、38%和 40%的蓝光、绿光和红光，而石耳素屏蔽了 81%、27%和 1%的这些波长范围。去除无羁萜会导致石黄衣在蓝光、绿光和红光中的光抑制增加程度相似，而石黄皮缺乏石耳素的地衣随着波长的降低，光抑制增加。无羁萜可能阻止水进入皮层中菌丝之间的空隙。充满空气的腔室带有白色无羁萜晶体，反射多余的光，而黄色化合物石耳素吸收多余的光。因此，无羁萜和石耳素都对地衣共生绿藻起到重要的光保护作用，但具有特定化合物的屏蔽机制。
