无机砷影响蛋白核小球藻光合活性的特征研究

采用蛋白核小球藻(Chlorella pyrenoidosa)进行无机砷毒性暴露实验,分析As(Ⅲ)和As(V)对蛋白核小球藻光合活性的影响差异.结果表明:该藻对无机砷具有较强的耐受性,在砷浓度大于37.5mg·L~(-1)暴露条件下,小球藻叶绿素a合成、光系统II(PSII)最大光量子产量(F_v/F_m)、实际光量子产量(Yield)及相关参数与无机砷浓度呈显著负相关,As(Ⅲ)对小球藻光合活性抑制作用显著高于As(V).As(Ⅲ)和As(V)150.0mg·L~(-1)暴露96h对小球藻光系统II影响差异最大,F_v/F_m、Yield、rETR_(max)和线性斜率(α)分别降低了77%,91%,92%,85%和19%,50%,51%,23%.透射电镜进一步表明,小球藻亚细胞结构形态受砷胁迫出现叶绿体片层间空泡化、类囊体基粒片层受挤压、蛋白核缩小及脂质滴.As(Ⅲ)对蛋白核小球藻光系统II(PSII)抑制作用大于As(V),可为深入了解无机砷对淡水微藻光合活性的影响机理提供一定的参考.

Influence of inorganic arsenic on photosynthetic activity of Chlorella pyrenoidosa

The arsenic contamination in aquatic environment has drawn significant attention to ecotoxic risk. The valence states of arsenic including arseniteAs(Ⅲ)] and arsenateAs(V)] play an important role for their behavior and toxicity at different levels of exposure concentrations. In this study, the toxicity of different concentrations of As(Ⅲ) and As(V) to Chlorella pyrenoidosa was determined and compared based on four different test endpoints:The growth inhibition rate, the chlorophyll a (Chl a) concentration, the chlorophyll fluorescence parameters of photosystem Ⅱ (PSⅡ) and the ultra-structural morphology of cells. The EC₅₀ values of As(V) were higher than As(Ⅲ), which indicated that As(Ⅲ) was more toxic to C. pyrenoidosa than As(V). The Chl a concentration of C. pyrenoidosa treated by As(V) was higher than that treated by As(Ⅲ). In general, the chlorophyll fluorescence parameters including the maximum quantum yields (F_v/F_m), the effective quantum yields (Yield), the maximum electron transport rate (rETR_max) and the linear section slope (α) of C. pyrenoidosa treated by 150.0 mg·L^-1 As(Ⅲ) for 96 h were decreased by 77%, 91%, 92% and 85%, which was higher than that exposed to As(V) of 19%, 50%, 51% and 23%, respectively, and chlorophyll fluorescence parameters were inhibited by high concentrations of both arsenic. The ultrastructural morphology of cells grown in the two species arsenic was observed by transmission electron microscopy. The cell wall separated from the cell membrane, accumulated starch granules were observed in the chloroplast, and diminishing pyrenoid and some lipid droplets were also observed in the cytoplasm. The mechanism of arsenite and arsenate toxicity to C. pyrenoidosa was explored, and the inhibition of PSⅡ photosynthetic efficiency to C. pyrenoidosa was determined. These results will help to develop an understanding of the biologically mediated environmental processes of arsenite and arsenate.