Anatomical characteristics and tissue localization of various flavonoid subclasses in Cotinus coggygria stem and leaf cross-sections

Abstract

Leaves, twigs and wood of Cotinus coggygria (Anacardiaceae) are employed in European and Chinese traditional medicine to treat skin and mucosal injuries, fever, diarrhea, emesis and to enhance appetite. While being a popular medicinal plant, ancient tinctorial species and common ornamental shrub, its anatomical characteristics and tissue localization of major groups of active compounds have not been studied yet, to the best of our knowledge. Freehand cross sections of the stem at different developmental stages, leaf lamina and petiole were performed. Tissue types were studied using conventional dyes (toluidine blue; congo red and malachite green). Folin-Ciocalteu reagent, shift reagents (ammonia) and Naturstoffreagenz A were used to complement light microscopy and autofluorescence observations of flavonoid localization. Microscopes of type Optika XDS-3FL inverted fluorescence, and Olympus BH-2 for observation in visible light were employed. C. coggygria stem has a typical secondary structure. The bark contains resin ducts placed in the phloem; in younger twigs they are limited by outer sclerenchyma arches. Vascular cambium generates distinct annual rings, with a porous structure. The vessel frequency is of 100 – 200 mm2, and their perforations are simple. Medullar rays are narrow (1 – 2 cells). Chalcone and aurone derivatives are present in inner wood rings aged at least 2 years, in earlywood parts. Leaves display epidermis with anomocytic stomata on the lower surface. A hypodermis is present on the adaxial side. The midrib contains four main vascular bundles and cambium. The phloem encloses resin secretory cavities. The center of the midrib is occupied by parenchyma. Palisade parenchyma is two cells deep, and spongy mesophyll is situated towards the abaxial side. Reducing flavonoids are present in leaf mesophyll.