大气湿沉降油菜体内铅的形态累积及氧化胁迫效应

大气沉降是叶菜类农作物可食部位重金属铅（Pb）累积的主要来源，但大气湿沉降下铅在油菜（Brassica chinensis L.）体内的形态累积特征及氧化胁迫效应，尚不十分清晰。通过模拟大气湿沉降铅胁迫，研究油菜体内重金属Pb的累积、亚细胞分布、化学形态特征及油菜抗氧化响应。结果表明，油菜可食部位Pb含量为1.72-6.35 mg/kg，超出标准（GB 2762-2017）4.73-20.16倍。Pb大量分布在油菜茎和叶的细胞壁中（52.14%-86.99%），以草酸盐沉淀的形式存在（20.07%-59.27%），这可能会导致Pb在可食部位的大量累积（>95%）。细胞壁的固持作用和Pb主要以草酸盐和不溶性磷酸盐存在，可能是油菜重要的解毒耐性机制之一。湿沉降铅胁迫可以增加叶和茎的丙二醛（MDA）含量，造成细胞的氧化损伤，抑制叶绿素的合成。油菜可以通过提高抗氧化酶（SOD、POD、CAT）活性（7.73%-346.91%），增加抗氧化剂（AsA和GSH）和可溶性物质（可溶性糖、可溶性蛋白）含量（9.11%-279.59%），来有效应对湿沉降Pb胁迫。抗氧化酶在叶中变化最大，过氧化物酶（POD）和过氧化氢酶（CAT）活性分别上升49.41%-91.62%和123.42%-346.91%。抗氧化剂则在根中变化最显著，抗坏血酸（AsA）和谷胱甘肽（GSH）含量分别上升了134.15%-182.93%和238.78%-279.59%。可溶性糖、可溶性蛋白、POD、CAT和GSH可能是油菜叶能缓解湿沉降Pb氧化胁迫的主要因素之一（P<0.05）。研究结果可加深对大气沉降下Pb在叶菜体内累积分布行为的理解，并为大气重金属胁迫地区农作物重金属风险评估提供一定的理论依据。

Chemical speciation accumulation and oxidative stress of lead in Brassica chinensis L. under atmospheric wet deposition

Atmospheric deposition is the main source of lead accumulation in the leafy vegetable crops, but the chemical speciation and oxidative stress of lead in Brassica chinensis L. under wet deposition have not been fully understood. In this study, the accumulation, subcellular distribution, chemical speciation of Pb and antioxidant response of Brassica chinensis L. by spraying different lead concentrations were investigated. The results indicated that the Pb concentrations in edible parts ranged from 1.72 to 6.35 mg/kg, which were in the range of 4.73-20.16 times above the standard (GB 2762-2017). Most of the Pb accumulated in the edible parts (>95%), while only a few (1.14%-3.11%) accumulated in the roots. The Pb in Brassica chinensis L was primarily distributed in the cell wall fraction, while the soluble fraction and organelle fraction accounted for a similar proportion. Oxalate and insoluble phosphate states were the main chemical speciation of Pb. The Pb concentrations in the leaves and stems cell wall accounted for 52.14%-86.99% of total accumulation, most of which were insoluble oxalate fractions, causing the high accumulation of Pb in the edible parts. The storage of large amounts of heavy metals in the cell wall, as well as the formation of less toxic oxalate and insoluble phosphate states, might be one of the important detoxification mechanisms of Brassica chinensis L. Wet deposition of Pb caused the oxidative cellular damage, increased malondialdehyde content in leaves and stems and inhibited chlorophyll synthesis, but it promoted the soluble sugars and soluble proteins. Brassica chinensis L. could effectively respond to wet deposition Pb stress by increasing the activity of antioxidant enzymes (superoxide dismutase, peroxidase, catalase)(7.73%-346.91%), as well as increasing the content of antioxidants (ascorbic acid, glutathione) and soluble substances (soluble sugars, soluble proteins)(9.11%-279.59%). The antioxidant enzyme activities had the biggest change in the leaves, increasing by 49.41%-91.62% and 123.42%-346.91% for peroxidase (POD) and catalase (CAT), respectively. While the most significant change of antioxidant occurred in the roots, accounting for 134.15%-182.93% and 238.78%-279.59% of total content for ascorbic acid (AsA) and glutathione (GSH), respectively. The possible main reason for Brassica chinensis L. leaves to alleviate oxidative stress were peroxidase, catalase, soluble sugars, soluble proteins and glutathione, because of the significant correlation between those and wet deposition Pb concentration (P<0.05). These results could improve our understanding of the distribution behavior of Pb in the vegetables, and provide a theoretical basis for the environmental risk assessment of crops in atmospheric heavy metal stress areas.