Ultraviolet-B radiation is known to harm most photosynthetic organisms with the exception of several studies of photosynthetic eukaryotes in which UV-B showed positive effects. In this study, we investigated the effect of acclimation to low UV-B radiation on growth and photosynthesis of the cyanobacterium Nostoc sphaeroides. Exposure to 0.08 W m-2 UV-B plus low visible light for 14 d significantly increased the growth rate and biomass production by 16% and 30%, respectively, compared with those under visible light alone. The UV-B acclimated cells showed an approximately 50% increase in photosynthetic efficiency (α) and photosynthetic capacity (Pmax ), a higher PSI/PSII fluorescence ratio, an increase in PSI content and consequently enhanced cyclic electron flow, relative to those of non-acclimated cells. Both the primary quinone-type acceptor and plastoquinone pool re-oxidation were up-regulated in the UV-B acclimated cells. In parallel, the UV-B acclimated colonies maintained a higher rate of D1 protein synthesis following exposure to elevated intensity of UV-B or visible light, thus functionally mitigating photoinhibition. The present data provide novel insight into photosynthetic acclimation to low UV-B radiation and suggest that UV-B may act as a positive ecological factor for the productivity of some photosynthetic prokaryotes, especially during twilight periods or in shaded environments.

中文翻译：

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适应低紫外线B辐射可增加光系统I的丰度和循环电子传递，并增强蓝藻Nostoc sphaeroides的光合作用和生长。

众所周知，紫外线-B辐射会损害大多数光合生物，但对光合作用的真核生物进行的多项研究除外，其中紫外线-B表现出积极的作用。在这项研究中，我们调查了适应低UV-B辐射对球形蓝细菌Nostoc sphaeroides的生长和光合作用的影响。与仅在可见光下相比，暴露于0.08 W m-2 UV-B加低可见光下14 d分别使生长速率和生物量产生分别增加16％和30％。与非UV-B适应的细胞相比，UV-B适应的细胞显示出约50％的光合效率（α）和光合能力（Pmax）增加，PSI / PSII荧光比更高，PSI含量增加，因此循环电子流增强适应的细胞。在适应UV-B的细胞中，初级醌型受体和质体醌库的再氧化都被上调。平行地，在暴露于升高的UV-B或可见光强度后，适应UV-B的菌落保持较高的D1蛋白合成速率，因此在功能上减轻了光抑制作用。目前的数据提供了对低UV-B辐射的光合适应的新颖见解，并表明UV-B可能是某些光合原核生物生产力的积极生态因素，尤其是在暮光时期或在阴凉的环境中。因此在功能上减轻了光抑制作用。目前的数据提供了对低UV-B辐射的光合适应的新颖见解，并表明UV-B可能是某些光合原核生物生产力的积极生态因素，尤其是在暮光时期或在阴凉的环境中。因此在功能上减轻了光抑制作用。目前的数据提供了对低UV-B辐射的光合适应的新颖见解，并表明UV-B可能是某些光合原核生物生产力的积极生态因素，尤其是在暮光时期或在阴凉的环境中。