ENDOGENOUS ETHYLENE REQUIREMENT FOR ADVENTITIOUS ROOT INDUCTION AND GROWTH IN TOMATO COTYLEDONS AND LAVANDIN MICROCUTTINGS IN-VITRO

The role of ethylene in the formation of adventitious roots in vitro was studied in tomato (Lycopersicon esculentum Mill. cv. UC 105) cotyledons and lavandin Lavandula officinalis Chair x Lavandula latifolia microshoots. Both systems were able to form roots on hormone-free medium evolving low amounts of ethylene. The addition of 20-50 mu M indole-3-acetic acid (IAA) inhibited root formation in tomato cotyledons while increasing ethylene production. Naphthaleneacetic acid (NAA, 3 mu M) stimulated root number in lavandin explants and induced a transient rise in ethylene evolution. Enhanced ethylene levels via the endogenous precursors 1-aminocyclopropane-1-carboxylic acid (ACC, 25-50 mu M) drastically impaired root regeneration and growth in tomato. In lavandin, 10 mu M ACC stimulated ethylene production and significantly inhibited the rooting percentage and root growth. Conversely, ACC enhanced the root number in the presence of NAA only. Severe inhibition of rooting was also caused by ethylene reduction via biosynthetic inhibitors, aminoethoxyvinylglycine (AVG, 5-10 mu M) in tomato, and salicylic acid (SA, 100 mu M) in lavandin. A strict requirement of endogenous ethylene for adventitious root induction and growth is thus suggested.