CO_2加富对两种海洋微绿藻的生长、光合作用和抗氧化酶活性的影响

Effects of CO_2 enrichment on growth, photosynthesis and activities of antioxidant enzymes of two marine micro-green-algae

研究了 CO2 加富对两种海洋微绿藻小球藻和亚心形扁藻的生长、光合作用和抗氧化酶活性的影响。实验结果表明 ,CO2加富 (含 5 0 0 0 μl/ L CO2 的空气 )促进小球藻和亚心形扁藻的生长。但两种藻对 CO2 加富的敏感性不同。CO2 加富对小球藻生物量影响的敏感性小于亚心形扁藻。CO2 加富使两种藻的干重和光合速率显著增加 ;可溶性蛋白含量显著下降 ;但两种藻的 Chla含量和 Car含量与对照相比变化不明显。高浓度 CO2 生长的小球藻和亚心形扁藻的 MDA含量比对照低 ,表明 CO2 升高可以减轻微藻的膜脂过氧化损伤 ,有利于膜脂稳定性的保持 ;在正常浓度 CO2 (36 0μl/ L )条件下 ,抗氧化酶 SOD、POD、CAT、GR的活性因藻种不同而存在很大差异 ,高浓度 CO2 (5 0 0 0μl/ L )培养条件使得这些抗氧化酶中的 SOD、CAT、GR的活性显著降低 ,而POD活性变化则不明显。 CO2 浓度升高可能导致抗氧化酶活性需求的减少 ,从而对藻的氧化损伤具有一定的保护能力。另外 ,光合速率、Chla含量和

Atmospheric levels of CO_2 are expected to double during the 21^(st) century. Many researches have been executed on the ecological impacts of elevated atmospheric CO_2 concentration on algae. Marine microalgae is a primary producer in aquatic ecosystems and half of the primary biomass production on our planet is based on aquatic ecosystems. In this experiment, the effects of enriched CO_2 (5000μl/L) on the growth, photosynthesis, activities of antioxidant enzymes of Chlorella sp. and Platymonas subcordiformis were investigated using physiological and biochemical methods. The results showed that while the growth rate of both Chlorella sp. and Platymonas subcordiformis was increased when culture medium was bubbled with enriched CO_2, there were differences in the degree of response between the two species of microalgae. Platymonas subcordiformis was more sensitive than Chlorella sp. to CO_2 enrichment. CO_2 enrichment increased the dry weight and photosynthetic rate of both species of microalgae while the soluble protein content decreased significantly. The chlorophylla (Chla) and carotenoids (Car) content did not change significantly as compared to the controls. The malonyldialdehyde (MDA) contents of Chlorella sp. and Platymonas subcordiformis grown under elevated CO_2 were lower than that of Chlorella sp. and Platymonas subcordiformis grown under ambient CO_2, which suggests that elevated CO_2 can ease the damage of membrane lipid peroxidation produced under ambient CO_2 and enhance remaining membrane lipid stability. In addition to affecting photosynthetic activity, increased CO_2 levels can also play a crucial role in a marine microalgae's response to oxidative stress. Oxidative stress is potentially experienced by all aerobic life in adverse circumstances, resulting in the formation of toxic oxygen species such as superoxide anion (O_2^(·-)), hydroxyl radical (OH~·), hydrogen peroxide (H_2O_2) and singlet oxygen (()~1O_2). In order to balance and control the risk of oxygen toxicity during the photosynthetic process, the plant cell has developed an antioxidative defense system, which consists of antioxidants and several enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione reductase (GR). Compared to ambient CO_2 (360μl/L), CO_2 enrichment (5000μl/L) significantly reduced the activities of SOD, CAT and GR, while the POD activity did not changed significantly. Elevated CO_2 can cause the necessity for antioxidant enzymes activities to be diminished, which in turn enhances the protective ability of microalgae when faced with oxidative damage. Great differences exist between the activities of SOD, CAT and GR in Chlorella sp. and Platymonas subcordiformis in both ambient CO_2 and elevated CO_2.