Characterisation of trichomes morphology and density in the genus Ocimum L

Non-glandular and glandular trichomes (GTs) found on the stem and leaves of many plants act as a physical barrier against biotic and abiotic stresses. GTs store and secrete various materials including essential oils, which are of great interest in food, cosmetic and pharmaceutical industries (Rehman et al., 2016) Members of Lamiaceae, including Ocimum L. (basil), produce essential oils which have potent antioxidant, antiviral, and antimicrobial properties which could be used for treating various ailments (Shahrajabian et al., 2020). In this comparative study, Ocimum’s trichomes ultra-structure, pattern and distribution on leaves have been investigated, at different developmental stages of several Ocimum species, varieties, cultivars, and types, using Scanning Electron Microscopy (SEM). In the genus, both capitate and peltate types of GTs were present which were densely distributed on the leaf surface as compared to hairy non-glandular trichomes. Moreover, in the young leaves the density of GTs was very high compared to the mature leaves. It has been reported that basil oil’ concentration is controlled by density, size, and relative proportion of both types of GTs (Maurya et al., 2019). This study provides the basis for further investigation of the genetic and chemical mechanisms involved in the production of essential oils in Ocimum.