Physiologia Plantarum 130: 543–551. 2007 Copyright ª Physiologia Plantarum 2007, ISSN 0031-9317 Expression of PIP1 and PIP2 aquaporins is enhanced in olive dwarf genotypes and is related to root and leaf hydraulic conductance Claudio Lovisolo a, * ,† , Francesca Secchi a,† , Andrea Nardini b , Sebastiano Salleo b , Rosalia Buffa c and Andrea Schubert a,d a Dipartimento di Colture Arboree, Universita ` di Torino, Via Leonardo da Vinci 44, 10095 Grugliasco, Italy b Dipartimento di Biologia, Universita ` di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italy c Dipartimento di Colture Arboree, Universita ` di Palermo, Viale delle Scienze 11, 90128 Palermo, Italy d IVV, CNR, Via Leonardo da Vinci 44, 10095 Grugliasco, Italy Correspondence *Corresponding author, e-mail: claudio.lovisolo@unito.it Received 1 December 2006; revised 22 January 2007 doi: 10.1111/j.1399-3054.2007.00902.x The expression of OePIP1.1 and OePIP2.1 aquaporins in root, stem and leaf was higher in Olea europaea L. (olive) plants carrying a dwarfing (D) clone as rootstock, than in plants carrying a vigorous (M) clone as rootstock. The highest difference of expression between plants with D and M rootstocks was detected in the root and for the PIP2 gene, the transcripts of which show a high water channel activity in oocytes. Compared with plants with M rootstock, plants with D rootstock showed reduced root and canopy biomass and reduced hydraulic conductance of the bulk root system (K root ). Hydraulic conductance of D roots was higher than that of M roots when K root was scaled by root DW, in agreement with a higher expression of PIP genes. Leaf hydraulic conductance scaled by unit leaf surface area was almost twice as high in leaves from D plants compared with that in leaves from M plants. Modification of root growth imposed by grafting M onto D and D onto M slightly changed expression levels of root OePIP1.1 gene, the transcripts of which show almost null water channel activity in oocytes, suggesting a role less evident for OePIP1.1 in root hydraulic reequilibration. The role of PIP aquaporin gene expression in partially compensating reductions of plant hydraulic conductance is discussed. Introduction Root-to-shoot water flow in well-hydrated plants equili- brates water transpirational loss, maintains turgor and vehiculates nutrients through the plant. Under a given water potential gradient, flow rate is determined by the hydraulic conductance of tissues and organs along the root-to-leaf water pathway (Tyree and Zimmermann 2002). In turn, the whole-plant hydraulic conductance is influenced by several factors, including xylem vessel dimensions (Lovisolo and Schubert 1998), the occurrence of cavitations and embolisms (Lo Gullo et al. 1998, Nardini et al. 2001, Sperry 2000) and/or the presence of Abbreviations – HPFM, high-pressure flow meter; MIP, major intrinsic proteins; NCBI, National Center for Biotechnology Information; PIP, plasma membrane-located subfamily † These authors contributed equally to this work. Physiol. Plant. 130, 2007 543