We previously reported that Arabidopsis indole-3-acetic acid (IAA)-methyltransferase-1 (IAMT1) catalyzes the conversion of IAA, an essential phytohormone, to methyl-IAA (MeIAA) and that IAMT1 plays an important role in leaf development. Here, we present the possible mechanisms of action of MeIAA in Arabidopsis. We showed that MeIAA was more potent than IAA in the inhibition of hypocotyl elongation and that MeIAA and naphthalene-acetic acid (NAA), but not IAA, rescued the hypocotyl gravitropic defects in dark-grown aux1. However, MeIAA was less potent than IAA in the inhibition of primary root elongation in light-grown seedlings, and could not rescue the agravitropic root phenotype of aux1. MeIAA had a stronger capacity to induce lateral roots than both IAA and NAA and rescued the defective lateral root phenotype of aux1 seedlings. However, its capacity to induce root hairs was weaker than IAA and NAA and did not rescue the defective root hair phenotype of aux1 seedlings. These data indicate that MeIAA is an inactive form of IAA. The different sensitivities to MeIAA among different organs probably resulted from different expression localization and capacities of a putative MeIAA esterase to convert MeIAA to IAA.

中文翻译：

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吲哚-3-乙酸甲酯在拟南芥中的可能作用机制。

我们之前报道过拟南芥吲哚-3-乙酸 (IAA)-甲基转移酶-1 (IAMT1) 催化 IAA（一种必需的植物激素）转化为甲基-IAA（MeIAA），并且 IAMT1 在叶片发育中起重要作用。在这里，我们介绍了 MeIAA 在拟南芥中的可能作用机制。我们表明，MeIAA 在抑制下胚轴伸长方面比 IAA 更有效，并且 MeIAA 和萘乙酸 (NAA)（而不是 IAA）挽救了暗生长的 aux1 中的下胚轴向重性缺陷。然而，MeIAA 在抑制光生长幼苗初生根伸长方面不如 IAA 有效，并且不能挽救 aux1 的向地根表型。MeIAA 具有比 IAA 和 NAA 更强的诱导侧根的能力，并挽救了 aux1 幼苗有缺陷的侧根表型。然而，其诱导根毛的能力比IAA和NAA弱，并且不能挽救aux1幼苗的有缺陷的根毛表型。这些数据表明 MeIAA 是 IAA 的非活性形式。不同器官对 MeIAA 的不同敏感性可能是由于假定的 MeIAA 酯酶将 MeIAA 转化为 IAA 的不同表达定位和能力所致。