Abstract:

In the present study, the microstructure of Gelsemium elegans vegetative organs was observed, and the alkaloids in plants were localized. Also, the antibacterial activity of the alkaloids was explored, and the antibacterial mechanism of the alkaloids was analyzed. The anatomical study of the structural characteristics of G. elegans vegetative organs was carried out with anatomical methods, and through histochemical staining, the alkaloids in the plant were localized. Microscopic observation results showed that the structure of G. elegans performed the typical characteristics of the dicotyledonous plants; the leaf of G. elegans was dorsiventral, and there were starch granules deposited in stem pith. The histochemical results showed that the vegetative organs of G. elegans contained alkaloids. Alkaloids were mainly distributed in the mesophyll tissue of leaves. In the stem, alkaloids were mainly distributed in stem epidermis, cortex cells and phloem parenchyma cells. Also, alkaloids were distributed in parenchyma cells of pith and ray cells. Yellow-brown sedimentation also could be observed in the cork cambium, the inner layer, the cortex, phloem parenchyma and ray cells of the rhizome. The antibacterial activity results showed that the G. elegans alkaloid had antibacterial activity against Listeria monocytogenes ATCC19115, Staphylococcus aureus ATCC25923, Staphylococcus aureus CMCC26003, Escherichia coli ATCC25922, Escherichia coli O157, Pseudomonas aeruginosa ATCC27853, and Pseudomonas aeruginosa CMCC10104. With the increase of alkaloid concentration, the antibacterial effect was also enhanced. The inhibitory effect on Listeria monocytogenes was the most obvious. After treatment with its minimum inhibitory and lethal concentrations, the morphology and internal structure of Staphylococcus aureus ATCC25923 and Escherichia coli O157 showed that both two kinds of bacteria changed in different degrees, such as rough surface, depression, rupture of the cell membrane and cell wall, overflow of internal substance and even cell lysis. The morphology of S. aureus changed at the minimum inhibitory concentration and the cell wall of E. coli was stratified. This indicated that G. elegans alkaloid destroyed the permeability of the cell membrane, impeded the formation of the cell wall, and lysed the bacteria. The cell death at the minimum lethal concentration might be caused by the loss and cleavage of the mechanical strength and permeability of the wall.

Key words: Gelsemium elegans Benth, anatomical structure, alkaloid distribution, bacteriostatic effect, bacteriostatic mechanism