Oxalic acid content and pharmacobotany study of the leaf blades of two species of Annona (Annonaceae)

Abstract

Annona muricata L. and A. squamosa L. are species of the Annonaceae family widely used in traditional medicine in Brazil for the treatment of noncommunicable diseases. However, this species may contain, for example, calcium oxalate crystals, that can precipitate in the kidneys and contribute to the formation of kidney stones. There are still few studies on the content of oxalic acid present in medicinal species. Thus, the objective of this work was to conduct a comparative anatomical and histochemical study between the species and determining its content of oxalic acid. Semipermanent histological slides were prepared, following common plant anatomy procedures, for analysis of the leaf blades in optical microscopy, polarization and scanning electron microscopy coupled with energy-dispersive X-ray spectrometry. To determine the total, soluble and insoluble oxalate content was used titration with potassium permanganate. The anatomical characterization allowed identifying the characters useful in the differentiation of the species and the druses. The histochemistry revealed the location of the metabolites and, along with the chemical microanalyses, demonstrated that the druses are of calcium oxalate. Annona squamosa presented the highest level of total oxalate. The study assists in the quality control of A. muricata and A. squamosa and brings new information on its oxalic acid content.