Plant Growth Regulation 22: 1–6, 1997. 1 c 1997 Kluwer Academic Publishers. Printed in the Netherlands. Ethylene involvement in in vitro organogenesis and plant growth of Populus tremula L. A. Gonz´ alez, L. Arigita, J. Majada & R. S´ anchez Tam´ es Lab. Fisiolog´ ıa Vegetal, Dpto. B.O.S., Fac. Biolog´ ıa, Univ. Oviedo, 33071 Oviedo, Spain (Correspondence should be sent to: Aida Gonz´ alez D´ ıaz, Lab. Fisiolog´ ıa Vegetal, Dpto. B.O.S., Facultad Biolog´ ıa, Universidad Oviedo, C/ Catedr´ atico Rodrigo Ur´ ıa s/n, 33071 Oviedo, Spain) Received 15 January 1997; accepted in revised form 15 January 1997 Key words: bud, ethylene, in vitro culture, organogenesis, Populus tremula L., root Abstract The role of ethylene in the organogenesis in vitro of nodal segments of poplar (Populus tremula L) was studied. The results indicate that there is a relationship between organogenesis and ethylene because inhibition of its synthesis with AVG, added to the standard MS medium containing naphthalene acetic acid (NAA) and 6-benzylaminopurine (BAP), inhibited shoot elongation, induction and development of buds and root formation. These effects were reversed when the explants were transferred to standard MS medium before 20 days and not later than 30 days after treatment. Conversely, 1-aminocyclopropane-1-carboxylic acid (ACC) and 2-chloroethylphosphonic acid (CEPA) stimulated all these responses. Explants cultured on MS medium produce ethylene during culture. Furthermore, AVG inhibited ethylene production whereas ACC and CEPA enhanced it. Therefore ethylene can be related with organogenesis in explants of Populus tremula L. Abbreviations: ACC = 1-aminocyclopropane-1-carboxylic acid; AVG = aminoethoxyvinylglycine; BAP = 6- benzylaminopurine; CEPA = 2-chloroethylphosphonic acid; MS = Murashige and Skoog medium; NAA = 1- naphthalene acetic acid. 1. Introduction In vitro growth and differentiation of plant cells and tissues are affected by the ethylene produced and which accumulates to physiologically active levels within the propagation enclosure [2, 18, 26]. The role of ethylene in in vitro morphogenesis has been assessed previously [12, 15, 27, 28] showing some positive effects on lateral bud growth [29, 31], adventitious bud formation [12, 28] and root forma- tion [9, 10, 11], processes which constitute the basic phenomena of plant propagation by in vitro culture. In other cases, it may be inhibitory as in Magnolia soulangeana Soul. shoot cultures [6] or during root regeneration from tomato leaf discs [4]. The correlation between the amount of ethylene produced and organogenesis through the outgrowth of buds and roots in vitro has been studied less than the role of ethylene in maturation and in vivo systems [7, 9, 11, 14, 29]. A clear distinction, however, has not always been established between the strict rela- tionship of ethylene with plant development, and the effect of the ethylene produced and accumulated in the atmosphere of the culture jar. In the work reported here, we studied the relation- ship between ethylene production and the capacity of shoot and root formation of Populus tremula L. nodal segments and their subsequent development at differ- ent stages of the in vitro multiplication phase. The effect of AVG, ACC and CEPA on the morphogenic capacity of cultured explants was also examined.