Secretory structures of croton gratissimus Burch. Var. gratissimus (Euphorbiaceae): Micromorphology and Histophytochemistry.
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Date
2018
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Abstract
Croton gratissimus Burch. variety (var.) gratissimus (Euphorbiaceae) has a widespread
distribution in tropical Africa and is frequently used in African traditional medicine to treat
various ailments. In South Africa, dried leaves of C. gratissimus are smoked to treat influenza,
colds and fever. Due to its extensive use in traditional medicine, research on the phytochemical
composition of C. gratissimus has been documented. According to literature, these
phytochemicals are possibly secreted or accumulated in secretory structures. However, little or
no research is available on the structures involved in the production and/or accumulation of
phytochemicals in C. gratissimus. Therefore, this study aimed to describe the micromorphology
of trichomes and laticifers from the leaves and stems of C. gratissimus as well as to identify the
possible site of synthesis of phytochemicals. Furthermore, the chemical composition and
antibacterial properties of phytochemicals in the leaves and stems were also determined. In
addition, the antibacterial activity of biosynthesised silver nanoparticles (AgNPs) from leaf and
stem crude extracts was also investigated. Microscopic investigations revealed the presence of
lepidote and glandular trichomes, and non-articulated unbranched laticifers on/in the leaves and
stems of C. gratissimus. The lepidote trichomes formed a dense indumentum over the abaxial
surface of leaves throughout all developmental stages, canopying the underlying glandular
trichomes. Laticifers were present in the leaves and stems and were predominantly associated
with the vascular tissue in both organs. All structures stained positive for alkaloids, phenolic
compounds and lipids with histochemical tests. Phytochemical analyses of the leaves and stems
revealed alkaloids, amino acids, phenolic compounds, flavonoids, carbohydrates, terpenoids,
saponins and fixed oils and fats in both leaf and stem extracts. The methanolic leaf and stem
extracts demonstrated weak to strong activities against various bacteria strains, which are
attributed to the several bioactive compounds identified from Gas Chromatography-Mass
Spectrometry (GC-MS) analyses. In addition, AgNPs were successfully biosynthesised from the
methanolic leaf and stem extracts. Particles synthesised from both extracts were spherical in
shape, but their size distribution differed between organs. Antibacterial assays demonstrated a
stronger activity of particles from leaf extracts compared to those from stems. These findings
corroborate the use of C. gratissimus in traditional medicine and indicate that various structures
are involved in the production of bioactive compounds which contribute to the medicinal
properties of this plant. Furthermore, the antibacterial activities exhibited by the extracts and
AgNPs suggest that C. gratissimus is a potential source of antibacterial agents.
Description
Masters Degree, University of KwaZulu-Natal, Durban.