Variação de metabólitos secundários relacionada a eventos de fogo em Rhamnidium elaeocarpum Reissek

Abstract

The aim of this work was broaden the discussion about the role of the metabolic composition from woody species against stress caused by fire. Thus, we collected the bark of Rhamnidium elaeocarpum (Rhamnaceae), an abundant species in environments with fire passage, in different fire histories in the Pantanal do Abobral. We performed spectrophotometric analysis to quantify total phenols and tannins, while HPLC-DAD-MS/MS was used to obtain profile and metabolic response to recent fire events in the region. Furthermore, we evaluated the thermogravimetric behavior to validate the thermotolerance of R. elaeocarpum and its relationship to secondary metabolites. We hypothesized that the species would present high concentrations of secondary metabolites in the barks after recent fire events. Moreover, we observed that the phenolic and tannin contents did not differ in the treatments, except for APD 20 (group with specimens with aerial structure death), demonstrating that the global phenolic metabolism of the species is not affected by recent fire events. It may be the result of a biochemical tolerance of the plant to the physiological stress caused by the fire regime, which has been operating for a long time in the region, or also an exaptation derived from post-fire environmental conditions. The different concentration found in the APD 20 group was probably due to the leaching process since the natural decomposition of the collected barks was noticeable. Altogether, 23 compounds were annotated, mainly proanthocyanidins oligomers, suggesting the formation of a phenolic barrier with antioxidant action. We observed a metabolic deviation caused by the fire affected so that the production of compounds of interest, mainly gallocatechin, is at the expense of the others. In addition to this, there was an increase in karwinaphthopyranones (substances toxic to the human body) with the passage of the 2020 fire. It making it necessary to alert the Pantanal due to its wide medicinal use. Finally, the results of the thermogravimetric behavior indicated that Rhamnidium elaoecarpum presents thermotolerance and that the secondary compounds are closely related to this characteristic. In general, we observed that fire causes important qualitative effects on the metabolism of R. elaeocarpum and persists for at least two years, but we cannot say whether it is due to an adaptive value or in response to adjacent factors in the environment.