Institute of Dendrology, Polish Academy of Sciences, Parkowa 5, 62-035, Kórnik, Poland.
Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704, Poznań, Poland.
Environ Pollut. 2020 Sep;264:114585. doi: 10.1016/j.envpol.2020.114585. Epub 2020 Apr 15.
Lead is a dangerous pollutant that accumulates in plant tissues and causes serious damage to plant cell macromolecules. However, plants have evolved numerous tolerance mechanisms, including ectomycorrhizae, to maintain cellular Pb at the lowest possible level. When those mechanisms are successful, Pb-exposed plants should exhibit no negative phenotypic changes. However, actual molecular-level plant adjustments at Pb concentrations below the toxicity threshold are largely unknown, similar to the molecular effects of protective ectomycorrhizal root colonization. In this study, we (1) determined the molecular adjustments in plants exposed to Pb but without visible Pb stress symptoms and (2) examined ectomycorrhizal root colonization (the role of fungal biofilters) with respect to molecular-level Pb perception by plant root cells. Biochemical, microscopic, proteomic and metabolomic studies were performed to determine the molecular status of Populus × canescens microcuttings grown in agar medium enriched with 0.75 mM Pb(NO). Noninoculated and inoculated with Paxillus involutus poplars were analyzed in two independent comparisons of the corresponding control and Pb treatments. After six weeks of growth, Pb caused no negative phenotypic effects. No Pb-exposed poplar showed impaired growth or decreased leaf pigmentation. Proteomic signals of intensified Pb sequestration in the plant cell wall and vacuoles, cytoskeleton modifications, H-ATPase-14-3-3 interactions, and stabilization of protein turnover in chronically Pb-exposed plants co-occurred with high metabolomic stability. There were no differentially abundant root primary metabolites; only a few differentially abundant root secondary metabolites and no Pb-triggered ROS burst were observed. Our results strongly suggest that proteome adjustments targeting Pb sequestration and ROS scavenging, which are considerably similar but less intensive in ectomycorrhizal poplars than in control poplars due to the P. involutus biofilter (as confirmed in a mineral study), were responsible for the metabolomic and phenotypic stability of poplars exposed to chronic mild Pb stress.
铅是一种危险的污染物，它在植物组织中积累，对植物细胞的大分子造成严重损害。然而，植物已经进化出许多耐受机制，包括外生菌根，以将细胞内的 Pb 维持在尽可能低的水平。当这些机制成功时，暴露在 Pb 下的植物应该没有负面的表型变化。然而，在低于毒性阈值的 Pb 浓度下，植物的实际分子水平的调整在很大程度上是未知的，类似于保护性外生菌根根定植的分子效应。在这项研究中，我们（1）确定了暴露在 Pb 下但没有明显 Pb 胁迫症状的植物的分子调整，（2）研究了外生菌根根定植（真菌生物过滤器的作用）与植物根细胞对分子水平 Pb 感知的关系。进行了生物化学、显微镜、蛋白质组学和代谢组学研究，以确定在琼脂培养基中生长的杂种杨树微扦插的分子状态，该培养基中含有 0.75 mM Pb(NO)。在两个独立的对照和 Pb 处理的比较中，分析了未接种和接种栓皮栎的杨树。经过六周的生长，Pb 没有造成负面的表型影响。没有 Pb 暴露的杨树表现出生长受损或叶片色素沉着减少。在慢性 Pb 暴露的植物中，细胞细胞壁和液泡中 Pb 螯合的增强、细胞骨架修饰、H-ATPase-14-3-3 相互作用以及蛋白质周转的稳定的蛋白质组学信号与高度代谢组学稳定性同时发生。根初生代谢物没有差异丰度；只观察到少数差异丰度的根次生代谢物，并且没有 Pb 触发的 ROS 爆发。我们的结果强烈表明，针对 Pb 螯合和 ROS 清除的蛋白质组调整，由于栓皮栎生物过滤器的作用（在一项矿物研究中得到证实），在与对照杨树相比，在外生菌根杨树中更为相似但强度较低，是暴露于慢性轻度 Pb 胁迫下的杨树的代谢组学和表型稳定性的原因。
