ACC Oxidase and ACC Synthase Expression Profiles after Leaning of Young Radiata (P. radiata D. Don) and Maritime Pine (P. pinaster Ait.) Seedlings Patricio Ramos • Claudio Valenzuela • Gregoire le Provost • Christophe Plomion • Carlos Gantz • Maria A. Moya-Leo ´n • Raul Herrera Received: 21 September 2011 / Accepted: 5 December 2011 Ó Springer Science+Business Media, LLC 2011 Abstract Loss of verticality in conifers affects the nor- mal wood development by inducing changes and chemical modifications in tree stems called compression wood. It is known that ethylene influences the response during this abnormal wood-forming process. The expression pattern of genes involved in the ethylene biosynthesis pathway during gravitropic response in gymnosperms has been identified in adult trees. Young seedlings of radiata pine were inclined to reveal the expression pattern of these genes by the quantitative real-time PCR (qRT-PCR) technique. The seedlings were exposed to gravitropic stimuli and har- vested after 2.5 and 10 h (early responses) of inclination, and after 24 h (late response). Sampling includes trans- verse cuts at three heights of the whole stem of inclined seedlings. Our data revealed that genes encoding for 1-aminocyclopropane-1-carboxylate oxidase (ACO) and 1-aminocyclopropane-1-carboxylate synthase (ACS) were differentially expressed during the time of leaning, and, interestingly, at the basal portion of radiata pine stems. Additionally, transcriptional analysis in maritime pine showed a conserved profile of gene activation in conifers, and in mature compression wood, ACO gene transcription was strongly upregulated. These results indicate that the concerted activation of genes involved in ethylene bio- synthesis could be responding to leaning signals in young radiata and maritime pine seedlings. Keywords ACC oxidase  ACC synthase  Ethylene biosynthesis  Gravitropism  Pinus radiata Introduction Stem cells from trees respond to gravity through the induction of differential growth between upper and lower sides. Displacement of stems by slope or other mechanical stress leading to loss of verticality and tilting of the trees results in the formation of reaction wood. This response is unilateral and creates physical wood strains that force the stem back toward its original vertical orientation (Scurfield 1973; Wilson and Archer 1977; Timell 1986). The process of gravitropism can be divided into three sequential steps: (1) gravity perception, (2) signal transduction, and (3) differential growth in elongating organs with the conse- quent asymmetric radial growth in the responding parts (Fukaki and Tasaka 1999; Haswell 2003). The signal transduction pathway that controls the response to incli- nation in young seedlings is still unclear but seems to be a response related to intrinsic growth direction, phytohor- mone distribution, and interaction (Timell 1986; Sundberg and others 1994; Little and Eklund 1999). Electronic supplementary material The online version of this article (doi:10.1007/s00344-011-9248-2) contains supplementary material, which is available to authorized users. P. Ramos  C. Valenzuela  M. A. Moya-Leo ´n  R. Herrera (&) Instituto Biologı ´a Vegetal y Biotecnologı ´a, Universidad de Talca, 2 Norte 685, Talca, Chile e-mail: raherre@utalca.cl G. le Provost  C. Plomion Institut national de la recherche agronomique (INRA), UMR Biogeco 1202, 69 route d’Arcachon, 33612 Cestas, France C. Gantz Forestal Mininco, Avenida Alemania 751, Los Angeles, Chile Present Address: C. Gantz Gerente de Propagacio ´n y Mejoramiento Gene ´tico, GreenWood Resources Chile SA, Teniente Luis Cruz Martinez 265, Los Angeles, Chile 123 J Plant Growth Regul DOI 10.1007/s00344-011-9248-2