Comparative Analysis of Leaf Architecture and Histochemistry in Schinus fasciculatus and S. gracilipes (Anacardiaceae)

Abstract

Schinus fasciculatus (Griseb.) I.M. Johnst and S. gracilipes I.M. Johnst are plants rich in secondary metabolites traditionally used for dye, fodder, and medicinal purposes. This work is a comprehensive comparative analysis of leaf architecture and histochemistry between the two species to determine the in situ localization of their secondary metabolites. Leaf anatomy was characterized by classical histological methods. Fresh leaf cross-sections were treated with ferric chloride, Fast Blue B, aluminium chloride, vanillin-HCl, 1% KOH, Sudan IV, Neu´s, NADI, Liebermann-Burchard, PAS, and lugol. The leaves of both species shared morphological traits suitable for survival in water-limited environments, such as amphistomacy and anomocytic stomata. Glandular and non-glandular trichomes were abundant in S. gracilipes suggesting that they have a protective role against biotic and abiotic stresses. Some features like mesophyll structure and thickness indicate S. fasciculatus leaves respond better to the selective pressure of extreme environments. The histochemical analysis revealed a widespread distribution of phenolic compounds and terpenoids in the mesophyll tissue of both species. Glandular trichomes contained polysaccharides, terpenoids and phenolic compounds, including flavonoids. Numerous schizogenous phloem ducts containing terpenoids were observed in both species, with alkaloids only present in the phloem ducts of S. fasciculatus. These findings suggest that terpenoids and phenolic compounds in both Schinus species serve as plant defenses and protect against environmental stresses. The distribution and abundance of tannins and flavonoids suggest they protect against excessive UV radiation and reactive oxygen species. The ecophysiological significance of the results are discussed in relation to other Anacardiaceae species.

Keywords:
Alkaloids; lipids; phenolic compounds; terpenoids

HIGHLIGHTS

Secondary metabolites were localized in leaves of Schinus shrubs.

Terpenoids and phenolic compounds were widely distributed in the leaves.

Phloem ducts contained lipids and alkaloids.

Glandular trichomes produce phenolics, terpenes and polysaccharides

Ecophysiological roles are inferred from distribution of the secondary metabolites