Amino acids serve as structural monomers for protein synthesis and are considered important biostimulants for plants. In this report, the effects of all 20-L amino acids in Arabidopsis primary root growth were evaluated. 15 amino acids inhibited growth, being l-leucine (l-Leu), l-lysine (l-Lys), l-tryptophan (l-Trp), and l-glutamate (l-Glu) the most active, which repressed both cell division and elongation in primary roots. Comparisons of DR5:GFP expression and growth of WT Arabidopsis seedlings and several auxin response mutants including slr, axr1 and axr2 single mutants, arf7/arf19 double mutant and tir1/afb2/afb3 triple mutant, treated with inhibitory concentrations of l-Glu, l-Leu, l-Lys and l-Trp revealed gene-dependent, specific changes in auxin response. In addition, l- isomers of Glu, Leu and Lys, but not l-Trp diminished the GFP fluorescence of pPIN1::PIN1:GFP, pPIN2::PIN2:GFP, pPIN3::PIN3:GFP and pPIN7::PIN7:GFP constructs in root tips. MPK6 activity in roots was enhanced by amino acid treatment, being greater in response to l-Trp while mpk6 mutants supported cell division and elongation at high doses of l-Glu, l-Leu, l-Lys and l-Trp. We conclude that independently of their auxin modulating properties, amino acids signals converge in MPK6 to alter the Arabidopsis primary root growth.

中文翻译：

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拟南芥初生根的生长通过生长素依赖性和独立机制以及 MPK6 激酶活性被多种不同的氨基酸抑制

氨基酸作为蛋白质合成的结构单体，被认为是植物的重要生物刺激剂。在本报告中，评估了所有 20-L 氨基酸对拟南芥初生根生长的影响。15 种氨基酸抑制生长，其中 l-亮氨酸 (l-Leu)、l-赖氨酸 (l-Lys)、l-色氨酸 (l-Trp) 和 l-谷氨酸 (l-Glu) 最活跃，它们抑制了两者初生根的细胞分裂和伸长。野生拟南芥幼苗和几种生长素响应突变体（包括 slr、axr1 和 axr2 单突变体、arf7/arf19 双突变体和 tir1/afb2/afb3 三突变体，用抑制浓度的 l-Glu、l 处理）的 DR5:GFP 表达和生长的比较-Leu、l-Lys 和 l-Trp 揭示了生长素反应的基因依赖性、特异性变化。此外，Glu、Leu 和 Lys 的 l-异构体，但 L-Trp 并未减弱根尖中 pPIN1::PIN1:GFP、pPIN2::PIN2:GFP、pPIN3::PIN3:GFP 和 pPIN7::PIN7:GFP 构建体的 GFP 荧光。氨基酸处理增强了根中 MPK6 的活性，对 l-Trp 的反应更大，而 mpk6 突变体在高剂量的 l-Glu、l-Leu、l-Lys 和 l-Trp 下支持细胞分裂和伸长。我们得出结论，独立于它们的生长素调节特性，氨基酸信号会聚在 MPK6 中以改变拟南芥主根的生长。