College of Horticulture, Nanjing Agricultural University, No. 1 Weigang, Nanjing, 210095, China.
Department of Biology, University of Hartford, 200 Bloomfield Avenue, West Hartford, CT, 06117, USA.
Environ Sci Pollut Res Int. 2020 Nov;27(32):40156-40170. doi: 10.1007/s11356-020-09918-3. Epub 2020 Jul 13.
Water contamination with cadmium (Cd) is a global environmental problem and its remediation becomes urgent. Phytoremediation using ornamental plants has attracted much attention for its advantages of cost-effectiveness and beautification of the environment. Nelumbo nucifera G. is a popular ornamental aquatic macrophyte with fast growth, large biomass, and high capacities for Cd accumulation and removal. However, information about Cd resistance and defense responses in N. nucifera is rather scarce, which restricts its large-scale utilization for phytoremediation. The phytohormone ethylene plays an important role in plant resistance to Cd stress, but the underlying mechanism remains unclear. In this study, we investigated morphophysiological responses of N. nucifera seedlings to Cd stress, and focused on the effects of ethylene on oxidative damage, Cd accumulation, and antioxidant defense system at the metabolic and transcript levels in leaves under Cd stress. Our results showed that Cd exposure led to leaf chlorosis and necrosis, coupled with an increase in contents of hydrogen peroxide, electrolyte leakage, and malondialdehyde, and decrease in chlorophyll content. Exogenous ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) application intensified Cd-induced stress responses and Cd accumulation, and increased ethylene production by inducing ACC synthase (ACS) gene NnACS. Such enhanced ethylene emission inhibited catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities, and modulated ascorbate (AsA) and glutathione (GSH) accumulation through transcriptional regulation of their respective metabolic genes. After ethylene action inhibitor silver thiosulfate (STS) supplementation, Cd-induced oxidative damage was abolished, and Cd content declined but still at a relatively high level. Blocking of ethylene perception by STS inhibited ethylene biosynthesis; enhanced CAT, APX, and GR activities and their transcript levels; increased AsA accumulation via inducing its biosynthetic genes; but reduced GSH content and NnGSH2 expression level. These results suggest that ethylene biosynthesis and signaling play an important role in N. nucifera response to Cd stress, and maintaining appropriate ethylene level and low ethylene sensitivity could improve its Cd tolerance via efficient antioxidant defenses.
水体镉污染是一个全球性的环境问题，其修复迫在眉睫。利用观赏植物进行植物修复因其具有成本效益和美化环境的优点而受到广泛关注。荷花（Nelumbo nucifera G.）是一种生长迅速、生物量大、对镉具有高积累和去除能力的受欢迎的水生观赏植物。然而，关于荷花对镉的抗性和防御反应的信息相当匮乏，这限制了其在植物修复中的大规模利用。植物激素乙烯在植物对镉胁迫的抗性中起着重要作用，但其中的机制尚不清楚。在本研究中，我们研究了荷花幼苗对镉胁迫的形态生理响应，重点研究了在镉胁迫下，乙烯对叶片代谢和转录水平的氧化损伤、镉积累和抗氧化防御系统的影响。研究结果表明，镉暴露导致叶片黄化和坏死，同时过氧化氢、电解质渗漏和丙二醛含量增加，叶绿素含量降低。外施乙烯前体 1-氨基环丙烷-1-羧酸（ACC）加剧了镉诱导的胁迫反应和镉积累，并通过诱导 ACC 合酶（ACS）基因 NnACS 的表达增加了乙烯的产生。这种增强的乙烯释放通过对其代谢基因的转录调控抑制了过氧化氢酶（CAT）、抗坏血酸过氧化物酶（APX）和谷胱甘肽还原酶（GR）的活性，并调节了抗坏血酸（AsA）和谷胱甘肽（GSH）的积累。补充乙烯作用抑制剂银硫代硫酸（STS）后，镉诱导的氧化损伤被消除，镉含量下降，但仍处于较高水平。STS 阻断乙烯感知抑制了乙烯的生物合成；增强了 CAT、APX 和 GR 的活性及其转录水平；通过诱导其生物合成基因增加了 AsA 的积累；但降低了 GSH 含量和 NnGSH2 的表达水平。这些结果表明，乙烯的生物合成和信号转导在荷花对镉胁迫的响应中起着重要作用，通过有效的抗氧化防御，维持适当的乙烯水平和低乙烯敏感性可以提高其镉耐受性。
