Essential oil yield and trichomes structure in two sweet marjoram (Origanum majorana L.) varieties under salt stress

Abstract

Origanum majorana L. shoots were investigated for their essential oil (EO) yield, composition and the structures responsible for its biosynthesis. Shoots EO was extracted by hydrodistillation and composition was determined by gas chromatography–mass spectrometry (GC-MS) method. Fresh Leaves were observed by light microscopy (LM). Plants were cultivated for 17 days in a basal medium supplemented with 75 mM NaCl. Salt decreased the essential oil yield in Tunisian variety (TV), but an increase was shown in Canadian variety (CV). Salt constraint induced a change in EO chemotype of two varieties. Their anatomical study showed three types of trichomes: (i) non-glandular, simple hairs; (ii) small, capitate glandular trichomes; (iii) and peltate glandular trichomes. Non-glandular trichomes provided of three types at the TV against two at the Canadian one at control. Indeed, with TV we observed; multicellular (M), bicellular (B) and unicellular (U) trichomes. Bicellular trichomes (BT) were observed in CV, and multicellular (MT) and bicellular (UT) in TV at salt constraint. The increase and the decrease of EO yield in CV and TV was respectively due to the presence of three type of EO secretion which seemed to make defect in Tunisian one. Key words: Trichomes, non-glandular, capitate, peltate, glandular, salt, chemotype.