Department of Botany, Faculty of Life Sciences, Government College University, Faisalabad, 38000, Pakistan.
Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad, Faisalabad, 38040, Pakistan.
Environ Sci Pollut Res Int. 2018 Jan;25(3):2958-2971. doi: 10.1007/s11356-017-0735-2. Epub 2017 Nov 16.
Lead (Pb) stress adversely affects in planta nutrient homeostasis and metabolism when present at elevated concentration in the surrounding media. The present study was aimed at investigation of organic acid exudations, elemental contents, growth, and lipid peroxidation in two wild plants (Amaranthus viridis L. and Portulaca oleracea L.), exhibiting differential root to shoot Pb translocation, under Pb stress. Plants were placed in soil spiked with lead chloride (PbCl) concentrations of 0, 15, 30, 45, or 60 mg Pb/kg soil, in rhizoboxes supplied with nylon nets around the roots. The plant mucilage taken from root surfaces, mirroring the rhizospheric solution, was analyzed for various organic acids. Lead stress resulted in a release of basified root exudates from both plants. Exudates of P. oleracea roots showed a higher pH. In both plants, the pH rising effect was diminished at the highest Pb treatment level. The exudation of citric acid, glutamic acid (in both plants), and fumaric acid (in P. oleracea only) was significantly increased with applied Pb levels. In both plant species, root and shoot Pb contents increased while nutrients (Ca, Mg, and K) decreased with increasing Pb treatment levels, predominantly in A. viridis. At 60 mg Pb/kg soil, shoot Na content of A. viridis was significantly higher as compared to untreated control. Higher Pb treatment levels decreased plant fresh and dry masses as well as the quantity of photosynthetic pigments due to enhanced levels of plant HO and thiobarbituric acid reactive substances in both species. Photosynthetic, growth, and oxidative stress parameters were grouped into three distinct dendrogram sections depending on their similarities under Pb stress. A positive correlation was identified between Pb contents of studied plants and secretion of different organic acids. It is concluded that Pb stress significantly impaired the growth of A. viridis and P. oleracea as a result of nutritional ion imbalance, and the response was cultivar-specific and dependent on exogenous applied Pb levels. Differential lipid oxidation, uptake of nutrients (Ca, Mg, and K) and exudation of citric acid, fumaric acid, and glutamic acid could serve as suitable physiological indicators for adaptations of P. oleracea to Pb enriched environment. The findings may help in devising strategies for Pb stabilization to soil colloids.
铅（Pb）胁迫会影响植物体内营养元素的平衡和代谢，如果周围介质中铅的浓度升高。本研究旨在研究两种野生植物（苋菜和马齿苋）在铅胁迫下的有机酸分泌、元素含量、生长和脂质过氧化，这些植物表现出不同的根到茎的铅转运。将植物置于土壤中，土壤中添加的氯化铅（PbCl）浓度分别为 0、15、30、45 或 60mg Pb/kg 土壤，在根系周围用尼龙网供应的根盒中。从根表面提取的植物粘液，反映了根际溶液，用于分析各种有机酸。铅胁迫导致两种植物的碱性根分泌物释放。马齿苋根的分泌物 pH 值更高。在两种植物中，最高 Pb 处理水平下，pH 值升高的效果减弱。柠檬酸、谷氨酸（两种植物）和富马酸（仅马齿苋）的分泌量随着施加的 Pb 水平的增加而显著增加。在两种植物中，根和茎的 Pb 含量随着 Pb 处理水平的增加而增加，而营养元素（Ca、Mg 和 K）则随着 Pb 处理水平的增加而减少，在苋菜中尤为明显。在 60mg Pb/kg 土壤下，苋菜的地上部 Na 含量明显高于未处理对照。较高的 Pb 处理水平降低了植物的鲜重和干重，以及两种植物的光合色素的数量，这是由于植物 HO 和硫代巴比妥酸反应物质水平的升高。光合、生长和氧化应激参数根据它们在 Pb 胁迫下的相似性分为三个不同的聚类部分。研究植物的 Pb 含量与分泌的不同有机酸之间存在正相关关系。研究结果表明，Pb 胁迫显著损害了苋菜和马齿苋的生长，导致营养离子失衡，这种反应是特定于品种的，取决于外源施加的 Pb 水平。不同的脂质氧化、营养元素（Ca、Mg 和 K）的吸收和柠檬酸、富马酸和谷氨酸的分泌可以作为马齿苋适应富含 Pb 环境的合适生理指标。这些发现可能有助于制定将 Pb 稳定到土壤胶体的策略。
