纳米氧化锌对细叶蜈蚣草(Egeria najas)光合作用的影响

采用细叶蜈蚣草(Egeria najas)作为受试植物，分别用不同浓度的ZnO NPs处理细叶蜈蚣草六天，通过OJIP荧光动力学曲线和脉冲瞬态荧光动力学曲线评估暴露在不同浓度的ZnO NPs悬浮液中的细叶蜈蚣草的光合性能。当细叶蜈蚣草暴露在ZnO NPs悬浮液中，光系统Ⅱ关闭的净速率（M_O）、J点的相对可变荧光强度（V_J）和单位反应中心用于热能耗散的能量（DI₀/RC）有明显的下降趋势（p<0.05），最大光化学量子效率（Φ_P0）、捕获的激子中用来推动电子传递的效率（Ψ₀）、电子传递的量子产额（Φ_E0）、实际光化学量子效率（′_PSⅡ）有上升的趋势（p<0.05）。表明ZnO NPs增强了光系统Ⅱ反应中心之间的连通性、促进了光系统Ⅱ受体侧的电子传递和光能的利用，即ZnO NPs在某些方面促进了细叶蜈蚣草的光合作用。用相应浓度的Zn2+溶液来处理细叶蜈蚣草，当细叶蜈蚣草暴露在Zn2+溶液中，光系统Ⅱ关闭的净速率、J点的相对可变荧光强度和单位反应中心用于热能耗散的能量有明显的上升趋势（p<0.05），最大光化学量子效率、捕获的激子中用来推动电子传递的效率、电子传递的量子产额、实际光化学量子效率有下降的趋势（p<0.05），单位反应中心吸收的光能（ABS/RC）、捕获的光能（TR₀/RC）和非调节性能量耗散量子产量（′_NO）有明显的上升趋势（p<0.05），即Zn2+降低了光系统Ⅱ反应中心之间的连通性、抑制了光系统Ⅱ受体侧的电子传递和光能的利用并使反应中心失活，即Zn2+抑制了细叶蜈蚣草的光合作用。在ZnO NPs处理细叶蜈蚣草的实验中并没有发现光合作用受抑制情况，表明ZnO NPs的促进作用强于其释放的游离Zn2+的抑制作用。

Effects of ZnO NPs on the Photosynthetic Processes of Egeria najas

In this study, we selected Egeria najas as the sample plant, which was exposed to different concentrations of Zinc oxide nanoparticles (ZnO NPs) suspensions for six days. The effects of different concentrations of ZnO NPs on photosynthetic processes of Egeria najas were explored respectively, by analyzing the O-J-I-P fluorescence induction dynamics curve and the pulse transient fluorescence induction dynamics curve. ZnO NPs strengthened the connectivity between photosystem Ⅱ (PSⅡ) units, promoted the efficiency of the electron transport at the acceptor side of PSⅡ and the utilization of the absorbed light energy, indicated by the significant decrease (p<0.05) in the net rate of PSⅡ closure （M₀）, the relative variable fluorescence intensity at phase J （V_J） and the effective dissipation of an active RC（DI₀/RC）, and the significant increase (p<0.05) in the maximum quantum yield of primary photochemistry （Φ_P0）, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than Q-_A（Ψ₀）, the quantum yield of electron transport （Φ_E0） and the effective quantum yield of electron transport at PSⅡ （′_PSⅡ） after exposure to ZnO NPs suspensions. These results suggested that ZnO NPs improved the photosynthetic performance to some degree. Corresponding concentrations of Zn2+ solution was also used to cultivate Egeria najas. Zn2+ lowered the connectivity between PSⅡ units, inhibited the electron transport at the acceptor side of PSⅡ and the utilization of absorbed light energy and damaged the PSⅡ reaction centers, as indicated by the significant increase (p<0.05) in the net rate of PSⅡ closure, the relative variable fluorescence intensity at phase J, the effective dissipation of an active RC, the effective antenna size of an active RC （ABS/RC）, the energy trapping capacity per active PSⅡ RC (TR₀/RC), and the quantum yield of dissipation through fluorescence and basal thermal processes （′_NO） and the significant decrease (p<0.05) in the maximum quantum yield of primary photochemistry （Φ_P0）, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than Ｑ-_A（Ψ₀）, the quantum yield of electron transport （Φ_E0） and the effective quantum yield of electron transport at PSⅡ （′_PSⅡ） after exposure to Zn2+ solution. These results suggested that Zn2+ inhibited photosynthetic processes of Egeria najas. When the sample plant was exposed to ZnO NPs suspensions, the effect of the Zn2+ released from ZnO NPs suspensions on the sample plant was not obvious, which meant that the enhancement was stronger than the inhibition.