Relationships Between Glandular Trichomes and Essential Oil Production in Ocimum basilicum and Ocimum sanctum (LAMIACEAE)

Abstract

Trichomes on the leaves, stem and flowers of Ocimum basilicum and O. sanctum were studied. The seeds of the plant materials were  collected from Nigeria and Pakistan, and planted at the Laboratory of the Department of Biological Sciences, COMSATS Institute of  Information Technology (CIIT), Islamabad, Pakistan. Three trichomes types are present in the two species, namely multicellular-non glandular, peltate glandular and capitate glandular trichomes, and this formed the basis for essential oil extraction from these parts  using Soxhlet extraction methods. Oils extracted were screened for the presence of alkaloids, terpenoids, phenol, tannins, saponins and  flavonoids. There is a correlation between the density of the glandular trichomes within and between the three parts of the two plants. The density of the glandular trichomes is higher in the plant parts that produce higher essential oil. Percentage oil yield is higher in the  leaves of O. sanctum (19.85%) and O. basilicum (13.58%), followed by the flowers and stem in the two plants. In line with the percentage oil  yields, the density of the glandular trichomes also followed a similar pattern; with higher density in the leaves (86.6mm² and  21.50mm²) for Ocimum sanctum and O. basilicum respectively, followed by the flowers and stem. Comparing the two species, O. sanctum  has a higher oil yield and higher density of glandular trichomes in all its parts than O. basilicum.