甲嘧磺隆亚急性暴露下盐生杜氏藻的生理生化响应

Physiological and Biochemical Responses of Dunaliella salina to Subacute Exposure of Sulfometuron-Methyl

作为一种磺酰脲类除草剂,甲嘧磺隆(Sulfometuron-methyl,SM)近年来已被国内部分近岸海域用于互花米草消杀。为探讨其对海洋微藻的毒性机理,将敏感物种盐生杜氏藻(Dunaliella salina)在3种亚急性浓度(0.0325、0.065和0.130 mg/L)的SM中暴露8 d,测定不同时间的藻细胞中乙酰羟酸合酶(AHAS)、支链氨基酸(BCAAs)、光合色素以及活性氧(ROS)、丙二醛(MDA)的活性(或含量)。研究表明,微藻的AHAS对SM具有高敏感性,其活性在低浓度SM下被显著抑制,此时未观察到光合色素和BCAAs合成受阻,表明该酶是SM的直接作用靶标。在中、低浓度SM暴露初期,微藻出现“毒物兴奋效应”,表现为3种BCAAs和3种光合色素的含量显著升高;在高浓度SM暴露初期或中期,3种BCAAs和叶绿素a的合成均受到抑制。此外,高浓度SM暴露期间,ROS和MDA的含量激增,表明藻细胞内出现氧化逆境。由此判断,当SM浓度逐渐增至0.130 mg/L时,微藻开始受到两方面不利影响:①AHAS活性降低使BCAAs合成受阻,进而导致蛋白质合成减少和初级代谢降低,使藻细胞对氧化逆境的耐受性变差;②藻细胞因代谢SM而产生过多ROS,造成膜脂过氧化发生,使蛋白质、色素等生物大分子受到氧化损伤。虽然AHAS对SM的高敏感性表明第一种影响早于第二种影响发生,但是,它们在高浓度SM下共同作用,将导致细胞受损程度加大甚至死亡。研究结果表明,AHAS活性抑制和ROS过量积累是SM对海洋微藻致毒的主要原因。

Sulfometuron-methyl(SM),as a sulfonylurea herbicide,has been used to eradicate Spartina alterniflora in some coastal waters of China in recent years.To explore its toxicity mechanism to marine microalgae,Dunaliella salina,a sensitive species,was exposed to three subacute concentrations(0.0325,0.065,and 0.130 mg/L)of SM for 8 days,and the activity/content of acetohydroxyacid synthase(AHAS),branched chain amino acids(BCAAs),photosynthetic pigments,reactive oxygen species(ROS),and malondialdehyde(MDA)in algal cells were measured at different times.The results indicated that AHAS in microalga has a high sensitivity to SM,and its activity is significantly inhibited even at low concentrations of SM while no obstruction in the synthesis of photosynthetic pigments and BCAAs was observed at this time,indicating that AHAS is a direct target of SM.At the initial stage of exposure to medium and low concentrations of SM,the microalga exhibited a hormesis,manifested by a significant increase in the content of three BCAAs and three photosynthetic pigments.However,during the early or middle stages of high concentration SM exposure,the synthesis of three BCAAs and chlorophyll a was inhibited.In addition,the sharp increase in contents of ROS and MDA occurred throughout the entire process of high concentration SM exposure,indicating the occurrence of oxidative stress in algal cells.It was deduced that as the SM concentration gradually increases to 0.130 mg/L,the microalga begins to be adversely affected in two aspects:①the decrease in AHAS activity hinders the synthesis of BCAAs,leading to a decrease in protein synthesis and primary metabolism,which in turn weakens the tolerance of algal cells to oxidative stress;②algal cells produce excessive ROS due to the metabolism of SM,causing membrane lipid peroxidation and oxidative damage to biological macromolecules such as proteins and pigments.Although the high sensitivity of AHAS to SM indicated that the first effect occurs earlier than the second one,their interaction at high concentrations of SM can increase cell damage and even cause death.The results of this study indicated that the inhibition of AHAS activity and excessive accumulation of ROS are the main causes of SM toxicity to marine microalgae.