Glandular Trichomes and Essential Oils of Developing Leaves in Mentha viridis lavanduliodora

Abstract

Mentha viridis lavanduliodora leaves were collected before, during, and after bloom at different stages of leaf ontogeny. They were analyzed in order to correlate the number of trichomes with the quantity and quality of the essential oils produced. The trichomes were counted and their density was determined using scanning electron microscopy (SEM). The oil was distilled, separated using gas chromatography, and the individual compounds were identified using mass spectrometry. The number of trichomes is highest before bloom, lowest during bloom, and then following bloom increases again at all stages of leaf development. There is a positive correlation between the quantity of oil and the number of trichomes before bloom, while during and following bloom a negative correlation was found. An analysis of variance (F-ratio) was calculated for the number of trichomes at different leaf lengths for each sampling period and between the number of trichomes and the leaf lengths during the three collecting periods. There are quantitative differences in the oils distilled. Before bloom the highest quantities of aliphatic hydrocarbons are present, while oxidized aliphatic hydrocarbon compounds reach their height during bloom, and esters are present in the greatest quantity after bloom. A dynamic synergism probably favors at different development stages the production of leaf trichomes (before and after bloom) or flower development and terpene derivative synthesis (during bloom).