Cadmium (Cd) is highly toxic to all organisms including plants, and recently tryptophan (Trp) pretreatment of plant seedlings is shown to improve Cd tolerance. But the underlying mechanism remains largely unknown. In this study, we used Arabidopsis (Arabidopsis thaliana) to determine the physiological relevance of Trp pretreatment in alleviating Cd toxicity in plants and explore its molecular mechanism with a focus on the metabolic pathways. The results showed that Trp pretreatment maintained the biomass and root lengths, relieved Cd-induced lipid peroxidation, and reduced Cd transport to the shoots, and eventually improved the response against Cd in Arabidopsis seedlings. The integrative analyses of the transcriptome and metabolome further revealed that Trp pretreatment alleviated Cd toxicity not only through a known mechanism of producing a major auxin indole-3-acetic acid and maintaining its levels, but also through two previously unrecognized mechanisms: increasing the area and strength of cell walls by promoting lignification to further reduce Cd entry, and fine-tuning Cd detoxification products derived from sulfur-containing amino acid metabolism. Our findings thereby provide deep mechanical insights into how Trp alleviates Cd toxicity in plants.

镉 (Cd) 对包括植物在内的所有生物体都具有剧毒，最近，植物幼苗的色氨酸 (Trp) 预处理被证明可以提高 Cd 耐受性。但潜在的机制在很大程度上仍然未知。在这项研究中，我们使用拟南芥（Arabidopsis thaliana) 以确定 Trp 预处理在减轻植物 Cd 毒性方面的生理相关性，并探索其分子机制，重点是代谢途径。结果表明，Trp 预处理维持了生物量和根长，减轻了 Cd 诱导的脂质过氧化，减少了 Cd 向枝条的运输，最终提高了拟南芥幼苗对 Cd 的反应。转录组和代谢组的综合分析进一步表明，Trp 预处理减轻 Cd 毒性不仅通过一种已知的产生主要生长素吲哚-3-乙酸并维持其水平的机制，而且还通过两种以前未被认识的机制：增加面积和通过促进木质化进一步减少 Cd 的进入来增强细胞壁的强度，微调源自含硫氨基酸代谢的 Cd 解毒产物。因此，我们的研究结果为 Trp 如何减轻植物中的 Cd 毒性提供了深入的机械见解。