UPLCMS/MS-based Untargeted Metabolic Profiling Reveals Changes in the Plumbago auriculata Lam. Metabolome Following Heteromorphic Incompatibility System Interactions

Background Heteromorphic self-incompatibility (HetSI), which is regulated by gametophytes, occurs in some species as a strategy to promote cross-pollination. Studies on HetSI are rare, and there is little evidence to establish the mechanism of HetSI. This research aimed to reveal metabolic changes occurring in HetSI. We used fluorescence microscopy as a tool to compare growth behavior in self-incompatible (SI) and self-compatible (SC) pollination in both pin and thrum flowers of Plumbago auriculata and to identify the ideal timepoint for sample collection for subsequent experiments. We also employed environmental scanning electron microscopy (ESEM) to evaluate intermorph structural differences in the pollen grain and stigmas in relation to heteromorphic self-incompatibility. Importantly, UPLC-MS/MS was applied in this study to identify metabolites, compare metabolic differences between pin and thrum styles and monitor metabolic changes in styles and SC and SI pollinations in the two type of flowers. Results The metabolites mainly included amino acids, flavonoids, glycosides/sugars, phenols, other organic acids, fatty acids/lipids, amines and alcohols. Surprisingly, high-energy nutrients such as amino acids, flavonoids, phenols alcohols and tricarboxylic acid cycle-related metabolites were found at higher levels in SI pollinations than in SC pollinations. Conclusion This result indicates that physiological changes in pollen-stigma interactions are different in pin, thrum styles and SC, SI pollinations and that energy deficiency may not be one of the reasons for HetSI.