Spatial distribution of structural elements in leaves of Ilex paraguariensis: physiological and ecological implications

Abstract

Calcium accumulation in crystals (mainly in the midrib) and silicon on the external surface of the upper epidermis suggests physiological and/or ecological roles. Concentration, form, and location of elements in leaf tissue of Ilex paraguariensis A. St.-Hil. can influence remobilization patterns and release of substances during its infusion for making yerba mate beverages. Even though, spatial distribution of elements and characterization of crystal formation in I. paraguariensis has not been elucidated. For filling this gap, this study used microanalytical techniques to evaluate accumulation and spatial distribution of elements in yerba mate leaves, which was done using chemical analyses and scanning electron microscopy combined with energy-dispersive spectroscopy (SEM–EDS). Chemical analyses confirmed high concentrations of potassium (K) and manganese (Mn) in leaves. Cell walls were predominantly composed of carbon (C) and oxygen (O). Compartmentalization of silicon (Si) occurred on the external surface of the upper epidermis between cell walls and the leaf cuticle. Precipitation of calcium (Ca) was higher in the midrib than in the leaf blade with the mesophyll and palisade mesophyll being the main accumulation sites. Microscopy–spectroscopy analysis revealed different patterns of elemental accumulation in leaves, which suggests physiological and/or ecological roles in yerba mate plants. Additionally, the abundance of Ca oxalates could explain the low Ca solubility during the beverage infusion process.