Abstract：
The defensive role performed by exogenously supplied ascorbic acid in the cyanobacterium Nostoc muscorum Meg1 against damages produced by UV-C radiation exposure was assessed in this study. Exposure to UV-C (24 mJ/cm2) significantly enhanced reactive oxygen species (ROS) (50%) along with peroxidation of lipids (21%) and protein oxidation (22%) in the organism. But, addition of 0.5 mM ascorbic acid prior to UV-C exposure showed reduction in ROS production (1.7%) and damages to lipids and proteins (1.5 and 2%, respectively). Light and transmission electron microscopic studies revealed that ascorbic acid not only protected filament breakage but also restricted severe ultrastructural changes and cellular damages in the organism. Although the growth of the organism was repressed up to 9% under UV-C treatment within 15 days, a pre-treatment with ascorbic acid led to growth enhancement by 42% in the same period. Various growth parameters such as photo-absorbing pigments (phycoerythrin, phycocyanin, allophycocyanin, chlorophyll a, and carotenoids), water splitting complex (WSC), D1 protein, RuBisCO, glutamine synthetase and nitrogenase activities in the UV-C treated organism were seen to be relatively intact in the presence of ascorbic acid. Thus, a detailed analysis undertaken in the present study was able to demonstrate that ascorbic acid not only act as first responder against harmful UV-C radiation by down-regulating ROS production, it also accelerated the growth performance in the organism in the post UV-C incubation period as an immediate response to an adverse experience presented in the form of UV-C radiation exposure.
摘要：
在这项研究中，评估了外源提供的抗坏血酸在蓝细菌NostocmuscorumMeg1中对UV-C辐射暴露造成的损害的防御作用。暴露于UV-C（24mJ/cm2）显着增强了生物体中的活性氧（ROS）（50％）以及脂质（21％）和蛋白质氧化（22％）。但是,在UV-C暴露之前添加0.5mM抗坏血酸显示ROS产生减少（1.7％）和对脂质和蛋白质的损害（1.5％和2％，分别)。光和透射电子显微镜研究表明，抗坏血酸不仅可以保护细丝的断裂，而且可以限制生物体内严重的超微结构变化和细胞损伤。尽管在15天内，在UV-C处理下，生物体的生长被抑制高达9％，在同一时期，用抗坏血酸预处理可使生长提高42％。各种生长参数，如光吸收颜料(藻红蛋白，藻蓝蛋白,别藻蓝蛋白,叶绿素a,和类胡萝卜素)，水分解复合体（WSC），D1蛋白，RuBisCO,在抗坏血酸存在下，UV-C处理的生物体中的谷氨酰胺合成酶和固氮酶活性相对完整。因此，在本研究中进行的详细分析能够证明，抗坏血酸不仅作为第一反应者，通过下调ROS的产生来对抗有害的UV-C辐射，作为对UV-C辐射暴露形式的不利经历的直接响应，它还加速了UV-C潜伏期后生物体的生长性能。
