Metabolomic understanding of pod removal effect in soybean plants and potential association with their health benefit

doi:10.1016/j.foodres.2020.109797

Food Research International

Volume 138, Part B, December 2020, 109797

https://doi.org/10.1016/j.foodres.2020.109797 Get rights and content

Highlights

•
Pod removal treatment on soybean plants induces significant metabolic perturbations in their leaves.
•
Leaves of soybean plants with pod removal treatment exhibited postponed senescence.
•
Beneficial health potential of soybean leaf were enhanced by pod removal treatment.

Abstract

Since natural materials, such as phytochemicals in plants, are increasingly being used for foods and skincare due to their beneficial functions, it is important for developing the cultivation practices to increase the contents of phytochemicals. We here explored metabolite perturbations in the leaves of soybean plants when their pods were removed during growth through ¹H NMR-based metabolomics approach. There were obvious metabolic differences in the leaves between normal and pod-removed soybean plants. High amounts of primary metabolites in pod-removed soybean leaves, including amino acids, sugars, and fatty acids, reflected a delay of leaf senescence caused by pod removal. In particular, amounts of isoflavones, coumestrol, and apigenin derivatives in pod-removed soybean leaves were substantially increased. These were considered as distinct metabolic influences of pod removal in soybean plants. These results indicate that pod removal of soybean plants can induce significant perturbations of various metabolites in their soybean leaves, providing useful information to improve the quality of soybean leaves by increasing amounts of bioactive components.

Graphical abstract

Introduction

Soybeans are rich in proteins, lipids, and carbohydrates. They are mostly utilized for food and dietary sources. Soybeans are also attracting attention as useful industrial materials. For example, soybean oil is considered as a future fuel source (Şensöz & Kaynar, 2006). Soybean protein-based biodegradable materials have been studied for alternatives of plastics (F. Song, Tang, Wang, & Wang, 2011). In addition, soybeans contain diverse phytochemicals, such as isoflavones, saponins, phytic acids, and phytosterols with beneficial potentials for health and amelioration of diseases (Isanga & Zhang, 2008). Due to these beneficial phytochemicals in soybeans, many studies have been carried out on the functionality of soybeans in various fields such as functional food and cosmetics industry.

Nowadays, people are paying attention to soybean leaves. Many scientific studies are still being carried out to improve their beneficial effects and have reported that soybean leaves also contain abundant bioactive phytochemicals. These phytochemicals in soybean leaves differ from those in soybean seeds and can contribute to beneficial effects as many functional food sources or supplements by maintaining health and alleviating metabolic disorders (Li et al., 2015, Li et al., 2019, Ryu et al., 2016, Zang et al., 2015). In general, a soybean leaf has trifoliolate shape consisting of three leaflets, and various flavonoid compounds are abundant in soybean leaves (Ho, Chen, Leung, Chan, Huang, & Chen, 2002). Flavonols and pterocarpans are major flavonoid compounds in soybean leaves. Their varieties and amounts are considerably affected by various conditions. For example, it has been reported that contents of kaempferol glycosides are decreased while levels of pterocarpans are increased as the growth stage reaches R8 growth stage when soybean seeds are fully mature (Song, Ryu, Lee, Jeong, Kim, & Oh, 2014). In addition, flavonoids such as apigenin, apigenin derivatives, coumestrol, and isoflavones are upregulated in the soybean leaves harvested from the volcanic area, demonstrating geographical influences in regulations of soybean leaf metabolites (Yun, Kang, Kim, Kim, Park, Choi, et al., 2018). Therefore, it is important to better understand interactions between perturbation of soybean leaf metabolome and various cultivation conditions to increase the synthesis of bioactive phytochemicals. It has been reported that pod removal treatment in plants could suppress leaf senescence, as indicated by delayed leaf abscission, yellowing, and browning (Crafts-Brandner and Egli, 1987, Lee et al., 2016, Mondal et al., 1978). However, there are no studies concerning pod removal effects in soybean plants on comprehensive metabolite perturbation of their leaves. Therefore, we eliminated pods from soybean plants and then performed ¹H NMR-based metabolomics study to explore changes in comprehensive metabolite profiles in soybean leaves.

Metabolomics facilitates the investigation of metabolome of soybean leaves as a contemporary omics technology to meet the demand for crop improvement. Metabolomics allows a holistic interpretation of complex metabolic networks in the biological pathway. It will undoubtedly help us to develop unique crops to enhance specific phytochemicals or metabolites. In particular, nuclear magnetic resonance (NMR)-based metabolomics have advantages of universal detection of metabolites with a wide range, a high reproducibility, a relatively simple implementation, and a provision of structural information for metabolite identification (H. K. Kim, Choi, & Verpoorte, 2010). Due to the high potential for soybean leaf materials, metabolomics has been applied to understand physiological responses of plants to different biotic and abiotic stresses. Such information could be used to improve soybean leaf quality. Our previous studies have employed ¹H NMR-based metabolomics on soybean leaves to investigate metabolic variations according to different cultivars, growth stage, and geographical location (Yun et al., 2018, Yun et al., 2016). From these studies, we could provide important information on strategies to improve the quality of soybean leaves having high amounts of bioactive compounds during cultivation.

The present study aimed to investigate metabolic variations and understand metabolic regulation of soybean leaves in response to pod removal treatment through ¹H NMR-based metabolomics approach.

Section snippets

Chemicals

For NMR analysis, coumestrol, methanol‑d₄ (CD₃OD, 99.8%) and deuterium oxide (D₂O, 99.9%) were purchased from Sigma Chemical Co. (St. Louis, MO, USA).

Soybean samples

Soybean cultivar used in this study was Glycine max (Shingi Kong_IT214697), and the soybean plants were harvested in Seoul National University Experimental Farm in Suwon, South Korea (37.3°N, 127.0°E). Fully matured trifoliate soybean leaves without pod removal were collected at the R7 stage as control by hand. Also, trifoliate leaves from

Identification of metabolites in the soybean leaves

Leaves of normal soybean plants, but not those of pod-removed soybean plants, turned yellow, withered, and started to fall at the R7 growth stage. Leaves of pod-removed soybean plants were still green and fresh. They did not start to fade before the R8 stage. Morphological differences in leaves between normal and pod-removed soybean plants were also observed (Fig. 1). Externally, it seemed that leaves of soybean plants with pod removal treatment exhibited postponed senescence compared with

Discussion

Although pod removal treatment in plants could suppress leaf senescence, as indicated by delayed leaf abscission, yellowing, and browning (Crafts-Brandner and Egli, 1987, Lee et al., 2016, Mondal et al., 1978), metabolic effects of pod removal have not been reported yet. Thus, we examined perturbations of the leaf metabolome in pod-removed soybean plants through ¹H NMR-based metabolomics approach to better understand metabolic changes in soybean leaves caused by pod removal. Pod removal

Conclusion

The present study revealed clear and large effects of pod removal on soybean plant, affecting a wide range of their leaf metabolites involved in primary and secondary metabolism. Such metabolite perturbations associated with delayed leaf senescence caused by pod removal resulted in marked increases of diverse bioactive compounds such as coumestrol, apigenin, and isoflavones. Therefore, results of this study provide useful information for developing herbal plant-based products rich in bioactive

CRediT authorship contribution statement

Dae-Yong Yun: Writing - original draft, Writing - review & editing, Investigation, Methodology, Project administration, Supervision, Writing - review & editing. Young-Gyu Kang: Writing - original draft, Writing - review & editing. Myoyeon Kim: . Donghyun Kim: . Eun-Hee Kim: . Young-Shick Hong: Writing - original draft, Writing - review & editing, Investigation, Methodology, Project administration, Supervision, Writing - review & editing.

Acknowledgments

We would like to thank the Korea Basic Science Institute (KBSI) for technical assistance with the 700 MHz and 900 MHz NMR experiments under KBSI program (Project No. D39701), and Professor Suk-Ha Lee at Seoul National University for cultivating and providing soybean plants.

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¹: These authors equally contributed to this work.

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Metabolomic understanding of pod removal effect in soybean plants and potential association with their health benefit

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Soybean samples

Identification of metabolites in the soybean leaves

Discussion

Conclusion

CRediT authorship contribution statement

Acknowledgments

Biomedicine & Pharmacotherapy

Plant Physiology and Biochemistry

International Journal of Pharmaceutics

Trends in Plant Science

Journal of Magnetic Resonance

Industrial Crops and Products

Food Research International

Food Chemistry

OPLS discriminant analysis: Combining the strengths of PLS-DA and SIMCA classification

Journal of Chemometrics

Statistical total correlation spectroscopy: An exploratory approach for latent biomarker identification from metabolic 1H NMR data sets

Analytical Chemistry

Acifluorfen-induced isoflavonoids and enzymes of their biosynthesis in mature Soybean leaves: Whole leaf and mesophyll responses

Plant Physiology

Sink removal and leaf senescence in soybean: Cultivar effects

Plant Physiology

Several biotic and abiotic elicitors act synergistically in the induction of phytoalexin accumulation in soybean

Plant Molecular Biology

Free amino acid profiles suggest a possible role for asparagine in the control of storage-product accumulation in developing seeds of low- and high-protein soybean lines

Journal of Experimental Botany

Soybean bioactive components and their implications to health—A review

Food Reviews International

Statistical total correlation spectroscopy: An exploratory approach for latent biomarker identification from metabolic ¹H NMR data sets