乙草胺胁迫对水华微囊藻光合生理特性的影响

Effects of Acetochlor Stress on Photosynthetic Physiology of Microcystis flos-aquae

除草剂乙草胺(ACT)施用后会通过灌溉侵蚀或地表径流等方式进入水环境造成污染。为探究ACT对浮游植物的影响,选择水华微囊藻作为受试生物,测定叶绿素a(Chl a)含量、叶绿素荧光参数、藻蛋白和藻胆蛋白相对含量的变化,观察藻细胞超微结构的变化,综合评估ACT对浮游植物光合作用的影响。结果表明,当ACT浓度≥0.1 mg·L-1时,Chl a含量开始显著降低(P<0.05);在低浓度(0.01~1 mg·L-1)ACT胁迫下,水华微囊藻能够通过自身调节,使得最大光合效率(F v/F m)、PSⅡ的实际光合效率(Y(Ⅱ))和快速光响应曲线不受ACT影响;而在高浓度(10~50 mg·L-1)处理组中,F v/F m、Y(Ⅱ)、快速光响应曲线、光响应曲线的初始斜率(α)和最大潜在相对电子传递速率(ETR max)均显著降低(P<0.05);别藻蓝蛋白(APC)、藻蓝蛋白(PC)和藻红蛋白(PE)的相对含量分别在ACT浓度为1、10和10 mg·L-1时开始显著降低(P<0.05)。这些结果说明,在高浓度ACT胁迫下,水华微囊藻的叶绿素合成受阻,光合色素减少,捕光能力、光能转化效率及相对电子传递速率均下降,光合活性降低,且ACT对藻胆蛋白的抑制作用顺序为别藻蓝蛋白>藻蓝蛋白>藻红蛋白,而半饱和光强(I k)显著增加(P<0.05),耐受能力增强,从而使光合作用受到抑制。透射电子显微镜结果表明,藻细胞结构会被ACT破坏,细胞变形且出现质壁分离,类囊体损伤且垂直于细胞壁,气泡、藻青素小粒和糖原减少,脂质颗粒增多,细胞内部紊乱,捕光色素减少,导致光合作用受阻。上述研究结果为全面评价ACT环境风险及农药的合理利用提供科学依据。

Because of extensive use,the herbicide acetochlor(ACT)has become a serious environmental pollutants by irrigation erosion or surface runoff,and the aquatic environment in our country has been severely polluted.In order to study the influences of ACT on phytoplankton,Microcystis flos-aquae was used as the model organism,and the changes of chlorophyll a content,chlorophyll fluorescence parameters,relative content of algal protein and phycobiliprotein,and the ultrastructure of algal cells before and after exposure to ACT were investigated,respectively.The results showed that the contents of Chl a significantly decreased when the concentrations of ACT were higher than 0.1 mg·L-1.The maximum photosynthetic efficiency(F v/F m),the actual photosynthetic efficiency of PSⅡ(Y(Ⅱ)),and Rapid Light Curve of Microcystis flos-aquae were not affected through self-regulation under the stress of lower concentrations(0.01~1 mg·L-1)of ACT,but these parameters as well as the initial slope of the light response curve(α),and maximum potential relative electron transfer rate(ETR max)were all significantly reduced(P<0.05)under the higher concentrations(10~50 mg·L-1)of ACT.The relative content of allophycocyanin(APC),phycocyanin(PC),phycoerythrin(PE),and phycoprotein significantly decreased in groups with ACT concentrations of 1,10 and 10 mg·L-1,respectively.The results indicated that chlorophyll synthesis of Microcystis flos-aquae was blocked under higher concentrations of ACT stress.The photosynthetic pigments,light-capturing capacity,light energy conversion efficiency,relative electron transfer rate,and photosynthetic activity were all reduced.The inhibition order of ACT on phycobiliproteins was allophycocyanin>phycocyanin>phycoerythrin.In addition,the semi-saturated light intensity(I k)increased significantly(P<0.05),and the tolerance was enhanced,which demonstrated that photosynthesis was supressed.Transmission electron microscopy results showed that the cells were deformed,evident plasmolysis was observed,the thylakoids were disarranged and perpendicular to the cell wall,and gas vesicle,cyanophycin granules and glycogen were largely absent,the increase of lipid,the internal disorder of cells and the decrease of light-harvesting pigment were also observed,which proved that the structures of algae cells were destroyed by ACT and led to an inhibition of photosynthesis.These results will not only provide scientific basis for comprehensive environmental risk evaluation of ACT but also help to guide the application of pesticides in agricultural setting.