Effects of the essential oil of Lippia gracilis Schauer on caulinary shoots of heliconia cultivated in vitro

the effects of thymol and carvacrol and the essential oil of lippia gracilis on caulinary shoots of heliconia were evaluated. after disinfection, the shoots were inoculated into ms medium and subjected to the treatments with 420 μl l-1 of essential oil (eo) of l. gracilis; 420 μl l-1 of thymol; 420 μl l-1 of carvacrol; 210 μl l-1 of thymol and 210 μl l-1 of carvacrol. the control treatment consisted of the ms medium without any phytoregulators. the main components of eo from l. gracilis are carvacrol, ρ-cimene, and thymol. seven days after the initiation of the experiments, 36.3% of the control treatment shoots were necrotized, but 90% of the caulinary shoots exposed to eo, thymol, or carvacrol appeared necrotized. transmission electron microscopy of the shoots revealed that the treatment with eo, thymol, or carvacrol caused the destruction of the plasma cell membranes, and the cell organelles and the nucleus were hardly evident. the eo and its main constituent were toxic to caulinary shoots of heliconia.