LGCgE, Equipe Sols et environnement, ISA, 59046, Lille Cedex, France.
Rev Environ Contam Toxicol. 2011;213:113-36. doi: 10.1007/978-1-4419-9860-6_4.
Lead has gained considerable attention as a persistent toxic pollutant of concern,partly because it has been prominent in the debate concerning the growing anthropogenic pressure on the environment. The purpose of this review is to describe how plants take lead up and to link such uptake to the ecotoxicity of lead in plants.Moreover, we address the mechanisms by which plants or plant systems detoxify lead.Lead has many interesting physico-chemical properties that make it a very useful heavy metal. Indeed, lead has been used by people since the dawn of civilization.Industrialization, urbanization, mining, and many other anthropogenic activities have resulted in the redistribution of lead from the earth's crust to the soil and to the environment.Lead forms various complexes with soil components, and only a small fraction of the lead present as these complexes in the soil solution are phyto available. Despite its lack of essential function in plants, lead is absorbed by them mainly through the roots from soil solution and thereby may enter the food chain. The absorption of lead by roots occurs via the apoplastic pathway or via Ca2+-permeable channels.The behavior of lead in soil, and uptake by plants, is controlled by its speciation and by the soil pH, soil particle size, cation-exchange capacity, root surface area,root exudation, and degree of mycorrhizal transpiration. After uptake, lead primarily accumulates in root cells, because of the blockage by Casparian strips within the endodermis. Lead is also trapped by the negative charges that exist on roots' cell walls.Excessive lead accumulation in plant tissue impairs various morphological, physiological, and biochemical functions in plants, either directly or indirectly, and induces a range of deleterious effects. It causes phytotoxicity by changing cell membrane permeability, by reacting with active groups of different enzymes involved in plant metabolism and by reacting with the phosphate groups of ADP or ATP,and by replacing essential ions. Lead toxicity causes inhibition of ATP production, lipid peroxidation, and DNA damage by over production of ROS. In addition, lead strongly inhibits seed germination, root elongation, seedling development, plant growth, transpiration, chlorophyll production, and water and protein content. The negative effects that lead has on plant vegetative growth mainly result from the following factors: distortion of chloroplast ultrastructure, obstructed electron transport,inhibition of Calvin cycle enzymes, impaired uptake of essential elements, such as Mg and Fe, and induced deficiency of CO2 resulting from stomatal closure.Under lead stress, plants possess several defense strategies to cope with lead toxicity. Such strategies include reduced uptake into the cell; sequestration of lead into vacuoles by the formation of complexes; binding of lead by phytochelatins,glutathione, and amino acids; and synthesis of osmolytes. In addition, activation of various antioxidants to combat increased production of lead-induced ROS constitutes a secondary defense system.
铅作为一种持久性有毒污染物备受关注，部分原因是它在日益增长的人为环境压力的争论中占据重要地位。本综述的目的是描述植物如何摄取铅，并将这种摄取与铅对植物的生态毒性联系起来。此外，我们还探讨了植物或植物系统解毒铅的机制。铅具有许多有趣的物理化学性质，使其成为一种非常有用的重金属。事实上，自文明诞生以来，人类就一直在使用铅。工业化、城市化、采矿和许多其他人为活动导致铅从地壳重新分配到土壤和环境中。铅与土壤成分形成各种复合物，而土壤溶液中存在的这些复合物中只有一小部分可被植物利用。尽管铅在植物中没有必需的功能，但它主要通过根系从土壤溶液中被吸收，从而可能进入食物链。根对铅的吸收是通过质外体途径或通过 Ca2+ 可渗透通道进行的。铅在土壤中的行为和被植物吸收受到其形态和土壤 pH 值、土壤粒径、阳离子交换能力、根表面积、根分泌物和菌根蒸腾程度的控制。铅被吸收后，主要积累在根细胞中，因为在内皮层的 Casparian 条带阻止了铅的进入。铅也被根细胞壁上的负电荷所捕获。植物组织中过量的铅积累会直接或间接地损害植物的各种形态、生理和生化功能，并引起一系列有害影响。它通过改变细胞膜通透性、与参与植物代谢的不同酶的活性基团反应、与 ADP 或 ATP 的磷酸基团反应以及取代必需离子来导致植物毒性。铅毒性通过产生过量的 ROS 抑制 ATP 产生、脂质过氧化和 DNA 损伤。此外，铅强烈抑制种子萌发、根伸长、幼苗发育、植物生长、蒸腾、叶绿素产生以及水和蛋白质含量。铅对植物营养生长的负面影响主要是由以下因素造成的：叶绿体超微结构扭曲、电子传递受阻、卡尔文循环酶抑制、必需元素如 Mg 和 Fe 的吸收受损，以及气孔关闭导致 CO2 供应不足。在铅胁迫下，植物具有几种防御策略来应对铅毒性。这些策略包括减少细胞内的摄取；通过形成复合物将铅隔离到液泡中；通过植物螯合肽、谷胱甘肽和氨基酸结合铅；以及合成渗透物。此外，激活各种抗氧化剂来对抗铅诱导的 ROS 增加构成了二级防御系统。
