Seasonal changes in the micromorphology, ultrastructure, and histochemistry of Carissa macrocarpa leaves

Carissa macrocarpa (Eckl.) A. DC., is a woody shrub of the family Apocynaceae used in traditional medicine. This study aimed to investigate the seasonal variations in micromorphology, ultrastructure, and histochemistry of C. macrocarpa leaves using light and electron microscopy and histochemical techniques. This novel micromorphological analysis revealed the presence of glandular trichomes consisting of a short stalk and multicellular head, located on the lower surface of the leaf. The leaf was characterized as hypostomatic, containing stomata only on its lower surface. Nonarticulated laticifers were interspersed in the leaf cortex and spongy parenchyma. Transmission electron microscopy of C. macrocarpa leaf sections showed the presence of mitochondria, vesicles, vacuoles, and chloroplasts containing starch grains and plastoglobuli. Histochemical analysis revealed a variety of phytochemicals such as proteins, alkaloids, phenols, resin acids, lipids, polyphenols, mucilage, pectin, lignin, and cutin in C. macrocarpa leaves. The chemical compounds found in the latex of its laticifers likely play a vital role in herbivory prevention. Although leaves can also be used for medicinal purposes due to the presence of many pharmacologically active metabolites, future toxicology studies of C. macrocarpa leaves are recommended to ensure their safety for medicinal use. This study is the first to describe the ultrastructure and histochemistry of C. macrocarpa leaves. Given the knowledge gap regarding this species, the present research provides a foundation for the future harvest and medicinal applications of C. macrocarpa.