Instituto do Mar e da Atmosfera (IPMA), Rua Alfredo Magalhães Ramalho, 6, 1495-006 Algés, Lisboa, Portugal.
MARE - Marine and Environmental Sciences Centre, Faculty of Sciences, University of Lisbon, Campo Grande, 1749-016 Lisbon, Portugal.
Sci Total Environ. 2019 Feb 10;650(Pt 1):111-120. doi: 10.1016/j.scitotenv.2018.08.335. Epub 2018 Aug 28.
The plant Halimione portulacoides, an abundant species widely distributed in temperate salt-marshes, has been previously assessed as bioindicator and biomonitor of mercury contamination in these ecosystems. The present study aims to assess uptake and distribution of total mercury (THg) and methylmercury (MMHg) within H. portulacoides, potential mercury release by volatilization through leaves, and toxicity and tolerance mechanisms by investigating plant photochemical responses. Stem cuttings of H. portulacoides were collected from a salt-marsh within the Tagus estuary natural protected area, and grown under hydroponic conditions. After root development, plants were exposed to HgCl and CHHgCl, and sampled at specific times (0, 1, 2, 4, 24, 72, 120, 168 (7 days) and 432 h (18 days)). After exposure, roots, stems and leaves were analysed for total Hg (THg) and MMHg content. Photobiology parameters, namely efficiency and photoprotection capacity, were measured in leaves. Both THg and MMHg were incorporated into the plant root system, stems and leaves, with roots showing much higher levels of both isotope enriched spikes than the other plant tissues. Presence of both mercury isotopes in the stems and leaves and high significant correlations found between roots and stems, and stems and leaves, for both THg and MMHg concentrations, indicate Hg translocation between the roots and above-ground organs. Long-term uptake in stems and leaves, leading to higher Hg content, was more influenced by temperature and radiation than short-term uptake. However, the relatively low levels of both THg and MMHg in the aerial parts of the plant, which were influenced by temperature and radiation, support the possibility of mercury release by stems and leaves, probably via stomata aperture, as a way to eliminate toxic mercury. Regarding photochemical responses, few differences between control and exposed plants were observed, indicating high tolerance of this salt marsh plant to THg and MMHg.
盐地碱蓬是一种广泛分布于温带盐沼中的丰富物种，此前已被评估为这些生态系统中汞污染的生物指示剂和生物监测物。本研究旨在评估盐地碱蓬对总汞 (THg) 和甲基汞 (MMHg) 的吸收和分布、通过叶片挥发释放潜在汞的情况，以及通过研究植物光化学响应来评估其毒性和耐受机制。从塔古斯河口自然保护区内的一个盐沼中采集盐地碱蓬茎段，并在水培条件下生长。根系发育后，植物暴露于 HgCl 和 CHHgCl 中，并在特定时间（0、1、2、4、24、72、120、168（7 天）和 432 小时（18 天））采样。暴露后，分析根、茎和叶中的总汞 (THg) 和 MMHg 含量。测量叶片中的光生物学参数，即效率和光保护能力。THg 和 MMHg 都被整合到植物的根系、茎和叶中，根中两种同位素富集峰的含量都明显高于其他植物组织。两种汞同位素都存在于茎和叶中，并且在根和茎之间，以及茎和叶之间，THg 和 MMHg 浓度都存在高度显著的相关性，这表明汞在根系和地上器官之间的转移。长期吸收茎和叶中的汞，导致汞含量较高，受温度和辐射的影响比短期吸收更大。然而，植物地上部分的两种 THg 和 MMHg 含量相对较低，受温度和辐射的影响，这支持了通过茎和叶释放汞的可能性，可能是通过气孔开度来消除有毒汞。关于光化学响应，在对照和暴露植物之间观察到很少的差异，表明这种盐沼植物对 THg 和 MMHg 具有很高的耐受性。
