Metabolomics analysis of developing Garcinia mangostana seed reveals modulated levels of sugars, organic acids and phenylpropanoid compounds

Mangosteen seeds are categorized as recalcitrant as they are sensitive to desiccation and low temperature. The seeds also do not go through the final developmental phase of maturation drying, hence, they are actively metabolic when they are shed. As such, metabolomics analysis could be useful to further understand mangosteen seed development. In this study, we used liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry approaches to analyze the profiles of polar compounds of mangosteen seeds harvested at four different stages of development (i.e. six, eight, 10 and 12 weeks after anthesis) and in mature seeds at 14 weeks. Principal component analysis (PCA) suggested temporal regulation of these metabolites during mangosteen seed development. Sugar levels such as glucose and fructose gradually increased throughout development, suggesting active metabolism until the mature stage. Organic acids such as citrate and malate as well as glycerol transiently increased during the seed growth phase which may imply their active energy and storage reserve production, respectively. High level of growth-related metabolites such as γ-aminobutyric acid found at discrete developmental stages infer their roles in the seed development. Furthermore, accumulation of secondary metabolites was active between 10 and 12 weeks after anthesis particularly metabolites related to phenylpropanoid pathway. The elevated levels of gambiriin A1, rutin, chlorogenic acid, 3-O-feruloylquinic acid, thymol-β-d-glucopyranoside and guaicol-β-d-glucopyranoside may enhance seed protection and defense. In conclusion, mangosteen seed displays recalcitrant seed characteristics, with metabolism geared to be germination-ready in terms of resources and seed defense.