Moustakas Michael, Malea Paraskevi, Haritonidou Katerina, Sperdouli Ilektra
Department of Botany, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece.
Division of Botany, Department of Biology, Faculty of Science, Istanbul University, 34134, Istanbul, Turkey.
Environ Sci Pollut Res Int. 2017 Jul;24(19):16007-16018. doi: 10.1007/s11356-017-9174-3. Epub 2017 May 23.
Photosynthetic activity, oxidative stress, and Cu bioaccumulation in the seagrass Cymodocea nodosa were assessed 4, 12, 24, 48, and 72 h after exposure to two copper oxide nanoparticle (CuO NP) concentrations (5 and 10 mg L). CuO NPs were characterized by scanning electron microscopy (SEM) and dynamic light scattering measurements (DLS). Chlorophyll fluorescence analysis was applied to detect photosystem II (PSII) functionality, while the Cu accumulation kinetics into the leaf blades was fitted to the Michaelis-Menten equation. The uptake kinetics was rapid during the first 4 h of exposure and reached an equilibrium state after 10 h exposure to 10 mg L and after 27 h to 5 mg L CuO NPs. As a result, 4-h treatment with 5 mg L CuO NPs, decreased the quantum yield of PS II photochemistry (Φ ) with a parallel increase in the regulated non-photochemical energy loss in PSII (Φ ). However, the photoprotective dissipation of excess absorbed light energy as heat, through the process of non-photochemical quenching (NPQ), did not maintain the same fraction of open reaction centers (q ) as in control plants. This reduced number of open reaction centers resulted in a significant increase of HO production in the leaf veins serving possibly as an antioxidant defense signal. Twenty-four-hour treatment had no significant effect on Φ and q compared to controls. However, 24 h exposure to 5 mg L CuO NPs increased the quantum yield of non-regulated energy loss in PSII (Φ ), and thus the formation of singlet oxygen (O) via the triplet state of chlorophyll, possible because the uptake kinetics had not yet reached the equilibrium state as did 10 mg L. Longer-duration treatment (48 and 72 h) had less effect on the allocation of absorbed light energy at PSII and the fraction of open reaction centers, compared to 4-h treatment, suggesting the function of a stress defense mechanism. The response of C. nodosa leaves to CuO NPs fits the "Threshold for Tolerance Model" with a threshold time (more than 4 h) required for induction of a stress defense mechanism, through HO production.
在暴露于两种氧化铜纳米颗粒（CuO NP）浓度（5和10 mg/L）后的4、12、24、48和72小时，对海草半叶马尾藻的光合活性、氧化应激和铜生物积累进行了评估。通过扫描电子显微镜（SEM）和动态光散射测量（DLS）对CuO NPs进行了表征。应用叶绿素荧光分析来检测光系统II（PSII）的功能，同时将叶片中铜的积累动力学拟合到米氏方程。在暴露的前4小时内吸收动力学很快，在暴露于10 mg/L的CuO NPs 10小时后以及暴露于5 mg/L的CuO NPs 27小时后达到平衡状态。结果，用5 mg/L的CuO NPs处理4小时，降低了PS II光化学的量子产率（Φ ），同时PSII中调节性非光化学能量损失（Φ ）平行增加。然而，通过非光化学猝灭（NPQ）过程将过量吸收的光能以热的形式进行光保护耗散，并没有维持与对照植物相同比例的开放反应中心（q ）。开放反应中心数量的减少导致叶脉中H₂O₂产量显著增加，这可能作为一种抗氧化防御信号。与对照相比，24小时处理对Φ 和q 没有显著影响。然而，暴露于5 mg/L的CuO NPs 24小时增加了PSII中非调节性能量损失的量子产率（Φ ），从而通过叶绿素的三重态形成单线态氧（¹O₂），这可能是因为吸收动力学尚未像10 mg/L那样达到平衡状态。与4小时处理相比，更长时间的处理（48和72小时）对PSII处吸收光能的分配和开放反应中心的比例影响较小，这表明存在应激防御机制的作用。半叶马尾藻叶片对CuO NPs的响应符合“耐受性阈值模型”，即通过H₂O₂产生诱导应激防御机制需要一个阈值时间（超过4小时）。
