Structure, biology and chemistry of plumbago auriculata (plumbaginaceae).

Abstract

Plumbago auriculata Lam. is endemic to South Africa and is often cultivated for its ornamental and medicinal uses throughout the world. Belonging to the family Plumbaginaceae this species contains specialized secretory structures on the leaves and calyces. This study focused on the micromorphological, chemical and biological aspects of the species. Micromorphological studies revealed the presence of salt glands on the adaxial and abaxial surface of leaves and two types of trichomes on the calyces. “Transefer cells” were reported for the first time in the genus. The secretory process of the salt glands was further enhanced by the presence of mitochondria, ribosomes, vacuoles, dictyosomes and rough endoplasmic reticulum cisternae. Histochemical and phytochemical studies revealed the presence of important secondary metabolites that possess many medicinal properties which were further analyzed by Gas chromatography-mass spectrometry (GC-MC) identifying the composition of compounds in the leaf and calyx extracts. A novel attempt at synthesizing silver nanoparticles proved leaf and calyx extracts to be efficient reducing and capping agents that further displayed good antibacterial activity against gram-positive and gram-negative bacteria. Biological studies revealed for the first time the presence of three variants of flower colour (white, pale blue and deep blue) and each colour had a characteristic sex-morph described as “Pin” or “Thrum.” Due to the “Pin” and “Thrum” scenario, plants are reported to be self-incompatible. However, the findings of this study suggested that plants were also self-compatibile. Graphical demonstration of calyx trichomes showed their involvement in insect entrapment often resulting in the death of the insect due to the struggle to free itself. This study concludes that P. auriculata is of good medicinal value and can contribute towards drug development and other medicinal uses in traditional markets as well as in the cosmetic and pharmacological industries. This species has striking morphological and biological features and possesses good value for future perspectives.