PHYSIOLOGIA PLANTARUM 114: 303–312. 2002 Copyright C Physiologia Plantarum 2002 Printed in Denmark – all rights reserved ISSN 0031-9317 Origin and basipetal transport of the IAA responsible for rooting of carnation cuttings Germa ´n Garrido b , Juan Ramo ´n Guerrero a , Emilio Angel Cano b , Manuel Acosta a and Jose ´ Sa ´nchez-Bravo a,* a Departamento de Biologı ´a Vegetal (Fisiologı ´a Vegetal), Facultad de Biologı ´a, Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain b Departamento de Investigacio ´n y Seleccio ´n, Barberet & Blanc S.A., E-30890 Puerto Lumbreras, Murcia, Spain * Corresponding author, e-mail: jsbravo/um.es Received 7 February 2001; revised 11 September 2001 The origin and transport of the IAA responsible for rooting was studied in carnation (Dianthus caryophyllus L.) cuttings obtained from secondary shoots of the mother plants. The presence of mature leaves in the cuttings was essential for rooting. Removal of the apex and/or the youngest leaves did not reduce the rooting percentage as long as mature leaves remained attached. Removal of mature leaves inhibited root- ing for a 24-day period during which the basal leaves grew and reached maturity. After this period rooting progressed as in intact cuttings. Auxin (NAA π IBA) applied to the stem base of defoliated cuttings was about 60% as effective as ma- ture leaves in stimulating rooting. Application of NPA to the basal internode resulted in full inhibition of rooting. The view, deduced from these results, that auxin from mature leaves is the main factor controlling the rooting process was reinforced by the fact that mature leaves contained IAA and exported labelled IAA to the stem. The distribution of radioactivity after application of (5– 3 H)-IAA to mature leaves showed that Introduction The involvement of endogenously produced indolyl-3- acetic acid (IAA) in adventitious rooting of stem cut- tings has been demonstrated in many plant species (see reviews by Jarvis 1986, Gaspar and Hofinger 1988). Most evidence is based on the inhibition of rooting after removal of the presumed endogenous auxin source by decapitation and/or debudding and restoration of root- ing when exogenous auxin is added (Haissig 1970, Elias- son and Areblad 1984), and after application of inhibi- tors of auxin polar transport (Katsumi et al. 1969, Liu and Reid 1992). These results suggest that IAA coming from the apex or buds and polarly transported in the Abbreviations – IAA, indolyl-3-acetic acid; IBA, indolyl-3-butyric acid; I T , intensity of IAA transport; NAA, naphthalenacetic acid; NPA, 1-N- naphthylphtalamic acid; PAT, polar auxin transport. Physiol. Plant. 114, 2002 303 auxin movement in the stem was basipetal and sensitive to NPA inhibition. The features of this transport were studied by applying 3 H-IAA to the apical cut surface of stem sections excised from cuttings. The intensity of the transport was lower in the oldest node than in the basal internode, probably due to the presence of vascular traces of leaves. Irrespective of the localization of the sections and the carnation cultivar used, basipetal IAA transport was severely reduced when the temperature was lowered from 25 to 4æC. The polar nature of the IAA transport in the sections was confirmed by the inhi- bition produced by NPA. Local application of IAA to differ- ent tissues of the sections revealed that polar auxin transport was associated with the vascular cylinder, the transport in the pith and cortex being low and apolar. The present results strongly support the conclusion that IAA originating from the leaves and transported in the stem through the polar auxin transport pathway was decisive in controlling adventitious rooting. stem is responsible for the rooting of cuttings. The chemiosmotic hypothesis of polar auxin transport pro- posed by Rubery and Sheldrake (1974) and Raven (1975), has been shown to be applicable to isolated seg- ments and intact plants (see reviews by Goldsmith 1977, Kaldewey 1984, Lomax et al. 1995, Leyser 1997, see also Johnson and Morris 1989). According to this theory, the basal localization of the efflux carrier in the transporting cells is responsible for the polar nature of auxin trans- port. This assumption has been recently confirmed by Gälweiler et al. (1998). Although experimental data in- dicate that polar auxin transport in stem is confined to