13c6&#45;glucose labeling of primary plant organs for mass spectrometric analysis

Primary Organ Identification in Medicinal Plants Using 13C6&#45;Glucose Labeling

The biosynthetic pathways of secondary metabolites in plants are intricate and diverse, involving highly specific and diverse accumulation organs1. At present, the specific synthesis sites and responsible organs for secondary metabolites in many medicinal plants are not well-defined. This ambiguity poses a significant obstacle to the strategic advancement and implementation of cultivation methods designed to optimize both the yield and quality of medicinal materials.
Molecular biology, biochemical, and isotope labeling techniques are extensively employed to unravel the synthesis pathways and sites of secondary metabolites in medicinal plants2,3,4,5, and each of these methodologies exhibits unique strengths and limitations, such as differences in efficiency and accuracy. Molecular biology approaches, for instance, offer high precision in pinpointing the sites within biosynthetic pathways but are notably time-intensive. Their utility is further constrained for species lacking publicly available genomic sequences, rendering these techniques less viable for such cases6. In contrast, isotope labeling techniques, employing isotopic ratios like 3C/12C, 2H/1H, and 18O/16O, provide a rapid and accessible means to investigate the synthesis, transport, and storage mechanisms of secondary metabolites7,8. They can reveal the spatial distribution of organic compounds and stable isotopes in leaves, thereby allowing the reconstruction of environmental conditions experienced by the leaves throughout their life cycle9. Furthermore, the application of external isotopic labels, such as 13C6-Glucose10 and 13C6-Phenylalanine11, enables the generation of carbon-labeled secondary metabolites, enhancing our understanding of their production and function.
Traditional carbon isotope labeling techniques encounter challenges in pinpointing the specific organs responsible for the synthesis of secondary metabolites due to the highly species-specific nature of their biosynthetic pathways and transport mechanisms. Liquid chromatography-mass spectrometry (LC-MS) has risen to prominence as a pivotal analytical instrument in this arena, offering a robust method for tracking exogenous isotopes in the chemical synthesis of drugs and investigating in vivo processes such as absorption, distribution, metabolism, and excretion12. The superior sensitivity, straightforwardness, and reliability of LC-MS make it an ideal choice for monitoring the production of secondary metabolites in plants13. In recent times, LC-MS has become increasingly favored for its application in external isotope labeling techniques, which enables the evaluation of labeling efficiency across different samples. This methodology provides critical insights into the primary organs engaged in the synthesis of secondary metabolites in medicinal plants, serving as an invaluable complement to biological methods for identifying the synthesis organs of these compounds14,15. Consequently, this approach not only facilitates the comparison of labeling efficiencies among various specimens but also sheds light on the key organs implicated in the generation of plant secondary metabolites, thereby enhancing our understanding of their biosynthesis.
We introduced a novel method that combines carbon isotope labeling with LC-MS detection to identify the primary organs responsible for synthesizing secondary metabolites in medicinal plants. Paris saponin (PS) has a variety of pharmacological activities such as anticancer, immunomodulation, and anti-inflammation16, and PPY is in increasing demand17. Therefore, we used PPY seedlings as research subjects and deciphered that leaves are the primary organ to synthesize the Paris saponin VII (PS VII) (Figure 1B) by using the 13C6-Glucose labeling associated with the LC-MS method. Our approach included four different treatments involving 13C6-Glucose feeding to leaf, rhizome, and stem-vascular bundles, as well as a non-feeding control. The choice of 13C6-Glucose is strategic, as it is swiftly metabolized into acetyl coenzyme A via respiration, which then facilitates PS synthesis. Employing the natural abundance of 13C, we utilized a Gas Chromatography-Stable Isotope Ratio Mass Spectrometer (GC-IRMS) system to assess the 13C/12C ratios across various plant organs and to analyze the isotopic ion peak ratios in PS VII and Paris saponins II (PS II) (Figure 1B) molecules. Our methodology, which leverages 13C-labeled plant secondary metabolite precursors and cutting-edge mass spectrometry techniques, offers a simpler and more accurate alternative to conventional carbon isotope labeling methods. This novel approach not only deepens our comprehension of the organs involved in secondary metabolite synthesis in medicinal plants but also lays a solid groundwork for future explorations into the biosynthetic pathways of these compounds.

Author Spotlight: Plant Primary Organs Profiling Using 13C6&#45;Glucose Labeling and LC&#45;MS

13C6&#45;Glucose Labeling Associated with LC&#45;MS&#58; Identification of Plant Primary Organs in Secondary Metabolite Synthesis

13C6&#45;Glucose Labeling of Primary Plant Organs for Mass Spectrometric Analysis

Research

JoVE Journal

Chemistry

This paper presents a novel and efficient method for certifying primary organs involved in secondary metabolite synthesis. As the most important secondary ...