Lorensen Marcus Daniel Brandbjerg Bohn, Bjarnholt Nanna, St-Pierre Benoit, Heinicke Sarah, Courdavault Vincent, O'Connor Sarah, Janfelt Christian
Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark.
Plant Biochemistry Laboratory and Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, 1871, Frederiksberg, Denmark.
Phytochemistry. 2023 May;209:113620. doi: 10.1016/j.phytochem.2023.113620. Epub 2023 Mar 1.
Monoterpenoid indole alkaloids (MIAs) are a large group of biosynthetic compounds, which have pharmacological properties. One of these MIAs, reserpine, was discovered in the 1950s and has shown properties as an anti-hypertension and anti-microbial agent. Reserpine was found to be produced in various plant species within the genus of Rauvolfia. However, even though its presence is well known, it is still unknown in which tissues Rauvolfia produce reserpine and where the individual steps in the biosynthetic pathway take place. In this study, we explore how matrix assisted laser desorption ionization (MALDI) and desorption electrospray ionization (DESI) mass spectrometry imaging (MSI) can be used in the investigation of a proposed biosynthetic pathway by localizing reserpine and the theoretical intermediates of it. The results show that ions corresponding to intermediates of reserpine were localized in several of the major parts of Rauvolfia tetraphylla when analyzed by MALDI- and DESI-MSI. In stem tissue, reserpine and many of the intermediates were found compartmentalized in the xylem. For most samples, reserpine itself was mainly found in the outer layers of the sample, suggesting it may function as a defense compound. To further confirm the place of the different metabolites in the reserpine biosynthetic pathway, roots and leaves of R. tetraphylla were fed a stable-isotope labelled version of the precursor tryptamine. Subsequently, several of the proposed intermediates were detected in the normal version as well as in the isotope labelled versions, confirming that they were synthesized in planta from tryptamine. In this experiment, a potential novel dimeric MIA was discovered in leaf tissue of R. tetraphylla. The study constitutes to date the most comprehensive spatial mapping of metabolites in the R. tetraphylla plant. In addition, the article also contains new illustrations of the anatomy of R. tetraphylla.
单萜吲哚生物碱（MIAs）是一大类具有药理特性的生物合成化合物。其中一种MIAs，利血平，于20世纪50年代被发现，并已显示出作为抗高血压和抗菌剂的特性。人们发现利血平在萝芙木属的各种植物物种中产生。然而，尽管其存在广为人知，但萝芙木在哪些组织中产生利血平以及生物合成途径中的各个步骤发生在哪里仍然未知。在本研究中，我们探索了基质辅助激光解吸电离（MALDI）和解吸电喷雾电离（DESI）质谱成像（MSI）如何通过定位利血平及其理论中间体来用于研究拟议的生物合成途径。结果表明，当通过MALDI-和DESI-MSI分析时，与利血平中间体相对应的离子在四叶萝芙木的几个主要部位被定位。在茎组织中，利血平和许多中间体被发现分隔在木质部中。对于大多数样品，利血平本身主要存在于样品的外层，这表明它可能作为一种防御化合物发挥作用。为了进一步确认不同代谢物在利血平生物合成途径中的位置，给四叶萝芙木的根和叶喂食了前体色胺的稳定同位素标记版本。随后，在正常版本以及同位素标记版本中都检测到了几种拟议的中间体，证实它们是在植物中由色胺合成的。在这个实验中，在四叶萝芙木的叶组织中发现了一种潜在的新型二聚体MIA。该研究构成了迄今为止对四叶萝芙木植物中代谢物最全面的空间图谱。此外，文章还包含了四叶萝芙木解剖结构的新插图。
