Text by Bin Liu
Eucalyptus globulus Labill. is a fast growing tree species with great economic and ecological values. In addition, the existence of wide range of foliar terpenoids and phenolics makes E. globulus an ideal reference plant for the study of specialized metabolites in plants. Our previous colleague Arooran Kanagendran and the team led by Prof. Ülo Niinemets have elaborately investigated the temporal response of terpenoids in E. globulus foliage upon ozone and wounding stresses (see also Kanagendran et al. 2018a, b). As an extension of previous study, in collaboration with colleagues from University of Copenhagen, we continued to dig out more about the other group of special phenolic metabolites, formylated phloroglucinol compounds (FPCs) in E. globulus foliage subjected to ozone and wounding stresses.
FPCs are a group of specialized metabolites consisting of a phloroglucinol-based derivative often attached with mono- or sesquiterpene moiety such as macrocarpals and euglobals. In fact, for the last two decades, much studies have been focusing on FPCs, particularly for elucidating chemical structures of novel FPCs, discovering pharmaceutical values, and elaborating herbivore deterring properties. However, the potential role of FPCs in plant resistance to environmental stresses has poorly been studied and that has motivated us to carry out the current study on exploring temporal variation in formylated phloroglucinols in E. globulus leaves in response to ozone and wounding stresses. In this study, we detected two groups of FPCs, macrocarpals and sideroxylonals in E. globulus leaf extracts, using a state-of-the art analytical instrument UHPLC-DAD-ESI-Q-TOF-MS/MS. The results indicated that there are differential and temporal regulations of different types of macrocarpals and sideroxylonals observed under separate and combined ozone and wounding treatments.
Moreover, considering the special chemical structure of FPCs, the pathway involved in in vivo synthesis of FPC would be deactivated to channel the enhanced biosynthesis of both terpenoids and phenolics, particularly upon stresses. Surprisingly, we explored that there were negative correlations between terpenoid emissions and FPC concentrations, which shed light on the first hint that competitions might exist for the biosynthesis of FPCs and terpenoids. Further studies investigating the temporal variation of FPCs in E. globulus upon different abiotic stresses and in different Eucalyptus species such as Eucalyptus nitens are highly warranted.
Citation: Liu, B., Marques dos Santos, B., Kanagendran, A., Neilson, E. H. J., & Niinemets, Ü. (2019). Ozone and Wounding Stresses Differently Alter the Temporal Variation in Formylated Phloroglucinols in Eucalyptus globulus Leaves. Metabolites, 9(3), 46. (link to full text)
Formylated phloroglucinol compounds (FPCs) are a class of plant specialized metabolite present in the Myrtaceae family, especially in the genus Eucalyptus. FPCs are widely investigated due to their herbivore deterrence properties and various bioactivities of pharmaceutical relevance. Despite the increasing number of studies elucidating new FPCs structures and bioactivity, little is known about the role of those compounds in planta, and the effects of environmental stresses on FPC concentration. Ozone (O3) and wounding are key stress factors regularly confronted by plants. In this study, we investigated how O3, wounding, and their combination affected individual and total FPC foliar concentration of the economically important species Eucalyptus globulus. Six individual FPCs, including five macrocarpals and one sideroxylonal, showed different response patterns to the single and combined stresses. Total macrocarpals only increased under single O3 treatment, whereas total sideroxylonals only increased in response to wounding treatment, suggesting different physiological roles played by the two groups of FPCs predominantly existing in E. globulus foliage. Total FPCs increased significantly under individual wounding and O3 treatments but not under the combined treatment. A principal component analysis indicated that all different treatments had unique FPC fingerprints. Total phenolic contents increased in all O3 and wounding treatments, and a marginally positive correlation was found between total FPCs and total phenolic contents. We suggest that, depending on the concentration and composition, FPCs play multiple physiological roles in planta, including serving as antioxidants to scavenge the reactive oxygen species brought about by O3 and wounding stresses.