四环素对微囊藻生长及光合作用的毒性效应机制

Toxic Effects of Tetracycline on the Growth and Photosynthesis in Microcystis aeruginosa

光合作用是蓝藻生长繁殖的生理基础,研究四环素胁迫下蓝藻的生长和光合作用的变化和响应,有助于揭示其作用机制。为探究四环素对微囊藻的毒性效应,对培养在0、0.1、0.2、0.5、1.0、2.0和5.0 mg·L-1共7个浓度下的微囊藻的细胞数、叶绿素a含量、微囊藻光合系统Ⅱ(PSⅡ)快速光响应曲线(RLCs)及快速叶绿素荧光诱导动力学曲线(OJIP)进行了测定。结果表明,四环素处理7 d后,微囊藻的半致死浓度(LC50)为(0.571±0.036) mg·L-1。随着四环素浓度的增加,微囊藻生长受到抑制,叶绿素含量减少,PSⅡ中单位反应中心失活。当四环素浓度高于0.5 mg·L-1时,微囊藻QA-到QB的电子传递被抑制,造成QA-大量积累,影响PSⅡ的电子受体侧。然而,在低浓度四环素处理中,以吸收光能为基础的性能指数(PIABS)、用于电子传递的量子产额(φEo)和最大光化学效率(φPo)显著升高,用于热耗散的量子比率(φDo)显著降低。这些结果表明,低浓度四环素处理时,微囊藻能通过自身调节改变PSⅡ中能量配置,改变电子传递速率,提高光合效率,从而应对低浓度四环素胁迫,而当四环素浓度较高时,微囊藻的光合作用显著降低,生长受到抑制。

Photosynthesis is a significant physiological foundation of the growth and propagation for cyanobacteria.Therefore, clarifying the response of the growth and photosynthesis of cyanobacteria to tetracycline stress will help to illuminate the response mechanisms. In order to investigate the toxic effects of tetracycline on cyanobacteria(Microcystis aeruginosa), the cells number, chlorophylla(Chla) content, photosynthetic rapid light curves(RLCs), and polyphasic Chla fluorescence transient curves(OJIP) were measured in M. aeruginosa inoculated into concentrations of 0, 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 mg·L-1 tetracycline, respectively. The results indicated that the median lethal concentration(LC50) of M. aeruginosa was(0.571±0.036) mg·L-1 after 7 d-culture. With the increase of tetracycline concentration, the growth and Chla content of M. aeruginosa were decreased and the reaction centers(RCs)in PSⅡ were inactivated. When the concentration of tetracycline was higher than 0.5 mg·L-1, the electron transfer of M. aeruginosa was inhibited from QA- to QB, resulting in a large accumulation of QA- at the electron acceptor side of PSⅡ. However, a significant rise in the performance index on absorption basis(PIABS), the quantum yield for electron transport(φEo) and the maximum quantum yield for primary photochemistry(φPo) and a significant decrease in the quantum ratio for heat dissipation(φDo) were found in 0.1 mg·L-1 and 0.2 mg·L-1 groups. These results suggested that M. aeruginosa could adjust the energy distribution in PSⅡ by enhancing the electron transfer rate and photosynthesis efficiency to adapt to low concentration tetracycline stress, while the photosynthesis and the growth of M. aeruginosa was significantly inhibited by high concentrations of tetracycline.