Department of Bioscience and Biotechnology, Fukui Prefectural University, 4-1-1 Matsuoka-Kenjojima, Eiheiji, Fukui 910-1195, Japan.
Faculty of Food and Agricultural Sciences, Fukushima University, Kanayagawa, Fukushima 960-1296, Japan.
J Agric Food Chem. 2020 Jun 17;68(24):6770-6775. doi: 10.1021/acs.jafc.0c00749. Epub 2020 Jun 8.
Plant hormones can act in synergistic and antagonistic ways in response to biotic and abiotic stresses and in plant growth and development. Thus, a technique is needed to simultaneously determine the distributions and concentrations of several plant hormones. Previously, we reported that localizations of two plant hormones [cytokinin (CK) and abscisic acid (ABA)] can be simultaneously visualized in a plant tissue using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). In MALDI-MS, however, self-ionization of an organic matrix occasionally interferes with ionizations of small molecules (<500 /) including most plant hormones. Another technique, nanoparticle-assisted laser desorption/ionization (Nano-PALDI), can avoid matrix self-ionization using nanoparticles to assist the ionization of analytes. Here, we compared the ionization efficiencies of common plant hormones by MALDI-MS and Nano-PALDI-MS. For the comparison, we prepared a standard mix of seven plant hormones [ABA, auxin (IAA), brassinosteroid (Br), two CKs (-zeatin, Z, and 6-(γ,γ-dimethylallylamino) purine, iP), jasmonic acid, and salicylic acid (SA)], an ethylene precursor (1-aminocyclopropane-1-carboxylic acid, ACC), and a heavy hydrogen-labeled ABA (D-ABA). Basic MALDI-MS detected all compounds except IAA, Br, and D-ABA, while Nano-PALDI-MS detected all nine compounds. By Nano-PALDI-MS imaging (MSI), each of the abovementioned hormones and ACC were also detected in root cross sections of rice which were incubated in the hormone mix for 2 h. In the elongation zone of untreated roots, Nano-PALDI-MSI revealed high levels of ABA and CKs in the outer part of roots and much lower levels in the stele, but Br, SA, and ACC were broadly distributed in the cross section. IAA seemed to be distributed in the epidermis, cortex, and stele. Multiple-hormone imaging using Nano-PALDI-MS has great potential for investigating the roles of hormone signaling in crop development and stress responses.
植物激素可以通过协同和拮抗作用来响应生物和非生物胁迫以及植物生长发育。因此，需要一种技术来同时测定几种植物激素的分布和浓度。以前，我们报道过可以使用基质辅助激光解吸/电离（MALDI）质谱（MS）同时观察植物组织中两种植物激素[细胞分裂素（CK）和脱落酸（ABA）]的定位。然而，在 MALDI-MS 中，有机基质的自电离偶尔会干扰包括大多数植物激素在内的小分子（<500 /）的离子化。另一种技术，纳米粒子辅助激光解吸/电离（Nano-PALDI），可以使用纳米粒子辅助分析物的电离来避免基质自电离。在这里，我们比较了 MALDI-MS 和 Nano-PALDI-MS 对常见植物激素的电离效率。为了进行比较，我们制备了七种植物激素[ABA、生长素（IAA）、油菜素内酯（Br）、两种 CK（-玉米素，Z 和 6-（γ，γ-二甲基烯丙基氨基）嘌呤，iP）、茉莉酸和水杨酸（SA）]、乙烯前体（1-氨基环丙烷-1-羧酸，ACC）和重氢标记的 ABA（D-ABA）的标准混合物。基本的 MALDI-MS 检测到除 IAA、Br 和 D-ABA 之外的所有化合物，而 Nano-PALDI-MS 检测到所有九种化合物。通过 Nano-PALDI-MS 成像（MSI），在将激素混合物孵育 2 小时的水稻根横切片中也检测到了上述激素和 ACC。在未处理根的伸长区，Nano-PALDI-MSI 显示 ABA 和 CKs 在根的外部部分含量较高，而在中柱中含量较低，但 Br、SA 和 ACC 在横截面上广泛分布。IAA 似乎分布在表皮、皮层和中柱中。使用 Nano-PALDI-MS 进行多激素成像对于研究激素信号在作物发育和应激反应中的作用具有巨大的潜力。
