Inulin contents and tissue distribution in underground storage organs of Asteraceae species from the Brazilian rocky fields

Abstract

Geophytes are widespread in rocky fields, having evolved to survive adverse environmental conditions mainly because of their underground storage organs and reserve compounds. Among these compounds, carbohydrates have several functions other than as an energy source, including protection against drought and extreme temperatures. In this work, we analyzed the composition and tissue distribution of carbohydrates in the underground organs of four Asteraceae species from a preserved area of rocky fields in the Brazilian Cerrado. Soluble carbohydrates were quantified and analyzed by HPAEC–PAD, and starch was analyzed by an enzymatic assay. All species (Baccharis subdentata DC., Chresta curumbensis (Philipson) H.Rob., Lessingianthus floccosus (Gardner) H.Rob., and Strophopappus glomeratus (Gardner) R.Esteves) store long-chain inulin-type fructans. Among them, C. curumbensis presented the highest amount of soluble carbohydrates, comprising 25% of the reserve organ dry mass. Inulin sphero-crystals were visualized under polarized light, mainly in the vascular cylinder. Buds were found on the underground organs of B. subdentata and C. curumbensis, and secretory structures were identified in S. glomeratus, L. floccosus, and C. curumbensis. The occurrence of buds, secretory structures, and fructans in these organs is probably related to ecophysiological strategies used as defense and survival mechanisms in response to stress conditions, particularly drought and fire, that occur frequently in rocky fields.