Reshika Ramasar

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.

Genus Carissa represents several species that are reported to be of great phyto-medicinal and ethnopharmacological value. However, Carissa macrocarpa is relatively understudied. Furthermore, environmental conditions such as seasonal changes are known to affect the phytochemical composition of medicinal plants. Therefore, this study aimed to investigate the phytochemical composition and biological activity of the leaf extracts of C. macrocarpa in the summer and winter seasons. The phytochemical screening of C. macrocarpa leaves showed positive results for a variety of phytochemicals, such as alkaloids, tannins, phenols, naphthoquinones, flavonoids, saponins, steroids, proteins, carbohydrates, mucilage, gum and resin. The methanolic extract was evaluated for its antibacterial activity against Escherichia coli and Staphylococcus aureus using the agar well diffusion method. The winter leaf extract was distinguished for its potential antibacterial activity against both bacterial strains with inhibition zones (mm) of 8.17 ± 1.04 and 6.83 ± 0.58 at 10 mg/mL. The antioxidant activity of the leaf extracts was evaluated using the 2, 2′-diphenyl-1-picrylhydrazyl (DPPH) assay. The percentage scavenging activities of the different extracts were significantly greater than that of the control. Furthermore, at 15, 30, 60, 120 and 240 µg/mL, the percentage scavenging activities of the winter methanol leaf extract were 74.65, 78.31, 85.45, 90.02 and 95.68%, and those of the summer one were 71.66, 73.57, 84.05, 88.22 and 96.28%, respectively, indicating that the methanol leaf extract had greater percentage scavenging activity in winter than in summer. In winter, the IC₅₀ value of the methanol leaf extract (0.67 µg/mL) was lower than that of ascorbic acid (8.26 µg/mL). It is concluded that winter is the optimal season to harvest leaves of C. macrocarpa for medicinal use. To the best of our knowledge, this is the first report that relates the phytochemical composition and medicinal properties of C. macrocarpa to changes in seasons. The results obtained are promising, and this species should be further explored to decipher its pharmacological worth.