Visualizing Genotypic and Developmental Differences of Free Amino Acids in Maize Roots With Mass Spectrometry Imaging
Visualizing Genotypic and Developmental Differences of Free Amino Acids in Maize Roots With Mass Spectrometry Imaging
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DOI：
10.3389/fpls.2020.00639
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发表时间：
2020-05-25
影响因子：
5.6
通讯作者：
Lee, Young Jin
中科院分区：
文献类型：
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作者：
O'Neill, Kelly C.;Lee, Young Jin
氨基酸是植物中必不可少的生物化合物，因为它们储存氮，一种必需的营养素，并且是驱动生物活性的蛋白质的构建块。在不同的植物系统中，已经使用各种各样的分析技术研究了氨基酸，然而，质谱成像（MSI）是一种特别有用的技术，因为它允许同时收集化学和空间信息。本研究利用基质辅助激光解吸电离（MALDI）-MSI技术，对玉米自交系B73和Mo 17及其正反交杂种根系中游离氨基酸的不同定位进行了研究。由于氨基酸难以在质谱法中检测，特别是直接在组织上检测，因此利用化学衍生化方案来提高电离效率并改善其检测。我们报告了B73和Mo 17玉米根中氨基酸的丰度和位置的差异，并表明杂交种显示出从双亲遗传特征的证据。大多数基因型差异出现在发育后期（10-11 cm长）种子附近的横截面（类似于2 cm远）。在这里，B73具有较低的氨基酸丰度，主要定位于大多数氨基酸的根中心，而Mo 17具有高得多的丰度，主要定位于根皮层。当在富含铵离子的条件下生长时，这种定位差异最小化。在N-15-铵离子存在下生长的根提供了关于氨基酸合成的额外见解。一些氨基酸，特别是亮氨酸/异亮氨酸和谷氨酰胺的定位不受氮的添加的影响，并且无论氮源是来自种子（N-14标记的）还是来自环境（N-15标记的）都是一致的。从环境中吸收的氮仅限于谷氨酰胺、天冬酰胺和丙氨酸，这与它们在氨基酸储存和运输中的作用一致。
Amino acids are essential biological compounds in plants as they store nitrogen, an essential nutrient, and are the building blocks for proteins that drive biological activity. Amino acids have been studied using a wide variety of analytical techniques in different plant systems, however, mass spectrometry imaging (MSI) is a particularly useful technique as it allows for the simultaneous collection of both chemical and spatial information. In this work, matrix-assisted laser desorption/ionization (MALDI)-MSI is used to study the different localization of free amino acids in the roots of maize inbred lines B73 and Mo17 and their reciprocal hybrids. Because amino acids are difficult to detect in mass spectrometry, especially directly on tissues, a chemical derivatization protocol is utilized to increase the ionization efficiency and improve their detection. We report differences in both abundance and localization of amino acids in B73 and Mo17 maize roots and suggest the hybrids show evidence of inheriting characteristics from both parents. Most genotypic differences are found in the cross-sections near the seed (similar to 2 cm away) at a later stage of development (10-11 cm in length). Here, B73 has lower amino acid abundance localized primarily to the center of the roots for most amino acids, while Mo17 has much higher abundance localized mainly to the root cortex. This difference in localization is minimized when grown in ammonium ion rich conditions. Roots grown in the presence of N-15-ammonium ions provided additional insight about the amino acid synthesis. The localization of some amino acids, particularly leucine/isoleucine and glutamine, is not affected by the addition of nitrogen and is consistent regardless of the nitrogen source, either from the seeds (N-14-labeled) or environment (N-15-labeled). Nitrogen uptake from the environment is confined to glutamine, asparagine, and alanine, consistent with their roles in amino acid storage and transportation.