Proteomic analysis in root tip of maize under cadmium and copper exposure

In this study, the metabolic adjustments performed by maize (Zea mays L) seminal roots exposed to 25 µM Cd2+ or 25 µM Cu2+ at pre-emergence are compared, focusing on the proteomic changes after metal exposure. Root width was increased, and root length was decreased after 72 h of metal treatment. Both metals induced H2O2 accumulation and lipid peroxidation in the root tip. These changes were accompanied by increases in lipoxygenase activity and 4-hydroxy-2-nonenal content. NMR spectroscopy revealed that the abundance of 38 water-soluble metabolites was significantly modified by Cd and Cu exposure; this set of metabolites comprised carboxylic acids, amino acids, carbohydrates, and unidentified phenolic compounds. Linoleic acid content significantly decreased in Cu-treated samples. The total amount of proteins detected in maize root apexes was 2,171. Gene ontology enrichment analysis of the differentially accumulated proteins was performed to detect pathways probably affected by metal additions. Both metals altered redox homeostasis, up-regulated oxylipins biosynthetic process, and shifted metabolism towards the oxidative pentose-phosphate in the root apexes. However, the methionine salvage pathway appears as a key metabolic module only under Cd stress. The integrative analysis carried out in this study suggests that most molecular features behind the reprogramming of maize root tips to cope with cadmium and copper toxicity are common, but some are not.

本研究对比了出苗前暴露于25 µM镉离子（Cd²+）或25 µM铜离子（Cu²+）的玉米（Zea mays L.）初生根的代谢调控过程，重点关注金属胁迫后的蛋白质组变化。经72小时金属处理后，玉米初生根的根粗增加、根长缩短。两种金属均诱导根尖产生过氧化氢积累与脂质过氧化现象，同时伴随脂氧合酶活性升高及4-羟基-2-壬烯醛含量上升。核磁共振波谱法（NMR）检测发现，镉与铜胁迫显著改变了38种水溶性代谢物的丰度，这类代谢物包括羧酸、氨基酸、碳水化合物以及未鉴定的酚类化合物。经铜处理的样本中，亚油酸含量显著降低。在玉米根尖中共检测到2171种蛋白质。本研究对差异积累蛋白开展了基因本体（Gene Ontology, GO）富集分析，以探究金属胁迫可能影响的通路。两种金属均改变了根尖的氧化还原稳态、上调氧脂素生物合成过程，并使代谢转向氧化戊糖磷酸途径。然而，仅在镉胁迫下，甲硫氨酸补救途径才作为关键代谢模块发挥作用。本研究的整合分析表明，玉米根尖应对镉与铜毒害的代谢重编程背后的多数分子特征是共通的，但仍存在部分特异性差异。