Copper (Cu) is an essential micronutrient for plants and as such is vital to many metabolic processes. Nevertheless, when present at elevated concentrations, Cu can exert toxic effects on plants by disrupting protein functions and promoting oxidative stress. Due to their proximity to the urbanised estuaries, seagrasses are vulnerable to chemical contamination via industrial runoff, waste discharges and leachates. Zostera muelleri is a common seagrass species that forms habitats in the intertidal areas along the temperate coast of Australia. Previous studies have shown the detrimental effects of Cu exposure on photosynthetic efficiency of Z. muelleri. The present study focuses on the impacts of sublethal Cu exposure on the physiological and molecular responses. By means of a single addition, plants were exposed to 250 and 500 μg Cu L⁻¹ (corresponding to 3.9 and 7.8 μM, respectively) as well as uncontaminated artificial seawater (control) for 7 days. Chlorophyll fluorescence parameters, measured as the effective quantum yield ($\varphi$PSII), the maximum quantum yield (Fv/Fm) and non-photochemical quenching (NPQ) were assessed daily, while Cu accumulation in leaf tissue, total reactive oxygen species (ROS) and the expression of genes involved in antioxidant activities and trace metal binding were determined after 1, 3 and 7 days of exposure. Z. muelleri accumulated Cu in the leaf tissue in a concentration-dependent manner and the bioaccumulation was saturated by day 3. Cu exposure resulted in an acute suppression of $\varphi$PSII and Fv/Fm. These two parameters also showed a concentration- and time-dependent decline. NPQ increased sharply during the first few days before subsequently decreasing towards the end of the experiment. Cu accumulation induced oxidative stress in Z. muelleri as an elevated level of ROS was detected on day 7. Lower Cu concentration promoted an up-regulation of genes encoding Cu/Zn-superoxide dismutase (Cu/Zn-sod), ascorbate peroxidase (apx), catalase (cat) and glutathione peroxidase (gpx), whereas no significant change was detected with higher Cu concentration. Exposure to Cu at any concentration failed to induce regulation in the expression level of genes encoding metallothionein type 2 (mt2), metallothionein type 3 (mt3) and cytochrome c oxidase copper chaperone (cox17). It is concluded that chlorophyll fluorescence parameters provide timely probe of the status of photosynthetic machinery under Cu stress. In addition, when exposed to a moderate level of Cu, Z. muelleri mitigates any induced oxidative stress by up-regulating transcripts coding for antioxidant enzymes.

铜（Cu）是植物必需的微量营养素，因此对许多代谢过程至关重要。然而，当铜以较高的浓度存在时，它会通过破坏蛋白质功能和促进氧化应激而对植物产生毒害作用。由于海草靠近城市化的河口，因此容易受到工业径流，废物排放和渗滤液的化学污染。Zostera muelleri是一种常见的海草物种，在澳大利亚温带海岸的潮间带形成栖息地。以前的研究表明，铜暴露对穆氏Z.光合作用效率的有害影响。本研究集中于亚致死性铜暴露对生理和分子反应的影响。通过单次添加，将植物暴露于250和500μgCu L ^-1（分别对应于3.9和7.8μM）以及未污染的人造海水（对照）中暴露7天。叶绿素荧光参数，以有效量子产率（$\varphi$PSII），最大量子产率（Fv / Fm）和非光化学猝灭（NPQ）每天进行评估，而叶片组织中的铜积累，总活性氧（ROS）以及抗氧化活性和痕量金属相关基因的表达在暴露1、3和7天后确定结合。Z. muelleri以浓度依赖的方式在叶片组织中积累铜，并且在第3天时生物积累达到饱和。$\varphi$PSII和Fv / Fm。这两个参数还显示出浓度和时间依赖性下降。在开始的几天内，NPQ急剧增加，然后在实验结束前下降。在第7天检测到Cu积累诱导了Z. muelleri的氧化应激，ROS水平升高。较低的Cu浓度促进了编码Cu / Zn超氧化物歧化酶（Cu / Zn-sod），抗坏血酸过氧化物酶（apx）的基因的上调。），过氧化氢酶（cat）和谷胱甘肽过氧化物酶（gpx），而较高的Cu浓度未发现明显变化。暴露于任何浓度的Cu均无法诱导2型金属硫蛋白编码基因的表达水平受到调控（mt2），3型金属硫蛋白（mt3）和细胞色素c氧化酶铜伴侣（cox17）。结论是，叶绿素荧光参数为铜胁迫下的光合机械状态提供了及时的探索。另外，当暴露于中等水平的铜时，穆勒氏梭菌通过上调编码抗氧化酶的转录本来减轻任何诱导的氧化应激。