Development, oil storage and dehiscence of peltate trichomes in Thymus vulgaris (Lamiaceae)

The development, oil storage and dehiscence mechanism of the peltate oil\u2013producing trichome in Thymus vulgaris L. was studied by conventional, fluorescence and electron scanning microscopy. A single epidermal initial forms the glandular trichome whose primordium becomes distinguishable from non\u2013glandular trichomes at its 3\u2013celled stage. The further divisions determine the formation of three functional compartments, (a) a basal reservoir cell, (b) an \u201cendodermal\u201d cell, and (c) a group of secretory head cells. At first, the gland head shows a bowl\u2013like shape with a folded cuticular covering that raises successively assuming a dome\u2013like form. During the differentiation of the gland cells, histochemical tests reveal the occurrence of a precise sequence of metabolic events: synthesis of RNA, proteins, glycoproteins, polysaccharides and, finally osmiophilic substances. At maturity, the cuticular sheath is formed by a non\u2013cellulosic polysaccharide framework on which the cuticle is deposed. Proceeding towards the senescence, the polysaccharide framework disappears and a large crescent shaped pore forms, whereby essential oils are released. Collected results are discussed in order to interpret gland function and essential oil production