Morfoanatomia, micromorfologia e histoquímica de órgãos vegetativos e reprodutivos de Hovenia dulcis Thunb. (Rhamnaceae)

Abstract

Hovenia dulcis Thunb. (Rhamnaceae), popularly known as "Japanese raisin tree," is a medicinal species widely used in Traditional Chinese Medicine. All its organs are used in various preparations, especially in the treatment of liver disorders, and it also has stomachic, antiparasitic, and diuretic properties. Despite its established traditional use, anatomical and histochemical studies supporting its botanical identification and the quality control of its raw materials are still scarce. This study aimed to characterize morphologically, anatomically, and histochemically the vegetative and reproductive organs of H. dulcis using light microscopy, scanning electron microscopy, and seventeen histochemical reagents for the detection of primary and secondary metabolites. Roots, stems, leaves, flowers, peduncles, and seeds of H. dulcis were collected, stored in ethanol, cut freehand into transverse and longitudinal sections, and subjected to double staining and histochemical reagents. Clearing was performed for analysis of the epidermal surfaces of the leaves, which were then stained with safranin. Morphologically, the species has taproots, a cylindrical stem, petiolate, oval, and alternate leaves, pentamerous and hermaphrodite flowers, fleshy and edible peduncles, dry capsule fruits, and oblong-elliptical seeds with linear hilum. Anatomically, the presence of secondary growth in the roots and stems, hypostomatic leaves with anomocytic and actinocytic stomata, a homogeneous palisade mesophyll, flowers with an ovary containing three anatropous ovules and structures adapted for pollination, peduncles with a large number of amyloplasts, and albuminous, oily seeds with palisade cotyledons are notable. Amyloplasts and starch grains were observed in various tissues, as were tector trichomes. Mucilaginous cavities were identified in all organs except roots and seeds, while phenolic idioblasts were found in all analyzed organs. Inorganic crystals with different morphologies and chemical compositions were detected in various tissues. Histochemical tests revealed the presence of mucilage, phenolic compounds, lipids, lignified tissues, pectic substances, proteins, alkaloids, and starch in different parts of the plant. The results provide relevant information for the botanical authentication of the species and the quality control of herbal products containing H. dulcis, in addition to contributing to taxonomic and systematic studies of the Rhamnaceae family.