Structural analogs of enzyme substrates involved in plant hormone biosynthesis can either inhibit or enhance hormone-related responses depending on their specific chemical characteristics. Ethylene is an important gaseous phytohormone regulating a myriad of physiological and developmental processes. The substrate of the ethylene biosynthesis key enzyme ACC oxidase (ACO), 1-aminocyclopropane-1-carboxylate acid (ACC), is the direct precursor of ethylene. Previous studies have identified a series of ACC analogs as ethylene antagonists competitively binding with ACO. Here, this study identified methyl 1-aminocyclopropanecarboxylate (methyl-ACC), a structural analog of ACC, as an agonist of ethylene response in plants. Methyl-ACC triggered enhanced ethylene-related responses in plants similar to the effects of ACC, such as restrained root elongation, increased root hair number, promoted dark-induced leaf senescence, and accelerated ripening of postharvest tomato fruit. A higher amount of ethylene release was detected from the tomato leaves treated with methyl-ACC than from the mock control. These bioactivities of methyl-ACC render it a potential plant growth regulator (PGR) for the agricultural and postharvest industries. RT-qPCR revealed a generally upregulated expression of the ethylene biosynthesis genes in detached tomato leaves under methyl-ACC treatment. In vivo and in vitro enzymatic activity analyses showed that methyl-ACC had no obvious effect on the total ACO activity in detached tomato leaves nor on the activity of recombinant SlACO1, the predominantly expressed ACO family member in this tissue. This study offers a promising new PGR and adds to the current knowledge on the structure–function-regulation relationship of compounds associated with ethylene biosynthesis. The mechanism by which methyl-ACC exerts its function is discussed.

参与植物激素生物合成的酶底物的结构类似物可以抑制或增强激素相关反应，具体取决于它们的特定化学特性。乙烯是一种重要的气态植物激素，可调节多种生理和发育过程。乙烯生物合成关键酶 ACC 氧化酶 (ACO)、1-氨基环丙烷-1-羧酸 (ACC) 的底物是乙烯的直接前体。以前的研究已经确定了一系列 ACC 类似物作为与 ACO 竞争性结合的乙烯拮抗剂。在这里，这项研究确定了 1-氨基环丙烷甲酸甲酯 (methyl-ACC)，一种 ACC 的结构类似物，作为植物中乙烯反应的激动剂。甲基-ACC 在植物中引发增强的乙烯相关反应，类似于 ACC 的作用，例如抑制根伸长，增加根毛数，促进暗诱导叶片衰老，加速番茄采后果实成熟。从用甲基-ACC 处理的番茄叶中检测到比模拟对照更高量的乙烯释放。甲基 ACC 的这些生物活性使其成为农业和采后工业的潜在植物生长调节剂 (PGR)。RT-qPCR 显示在甲基-ACC 处理下，离体番茄叶片中乙烯生物合成基因的表达普遍上调。甲基 ACC 的这些生物活性使其成为农业和采后工业的潜在植物生长调节剂 (PGR)。RT-qPCR 显示在甲基-ACC 处理下，离体番茄叶片中乙烯生物合成基因的表达普遍上调。甲基 ACC 的这些生物活性使其成为农业和采后工业的潜在植物生长调节剂 (PGR)。RT-qPCR 显示在甲基-ACC 处理下，离体番茄叶片中乙烯生物合成基因的表达普遍上调。体内和体外酶活性分析表明，甲基-ACC 对离体番茄叶片中的总 ACO 活性和重组 SlACO1（该组织中主要表达的 ACO 家族成员）的活性没有明显影响。这项研究提供了一种有前途的新 PGR，并增加了目前关于与乙烯生物合成相关的化合物的结构-功能-调节关系的知识。讨论了甲基-ACC发挥其功能的机制。