Environmental and Experimental Botany 68 (2010) 83–90 Contents lists available at ScienceDirect Environmental and Experimental Botany journal homepage: www.elsevier.com/locate/envexpbot The response of broccoli plants to high temperature and possible role of root aquaporins María Iglesias-Acosta a , M. Carmen Martínez-Ballesta a , José Antonio Teruel b , Micaela Carvajal a,∗ a Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Campus Universitario de Espinardo, Apdo. de Correos 164, 30100 Murcia, Spain b Departamento de Bioquímica, Universidad de Murcia, Campus de Espinardo, 30100 Espinardo, Murcia, Spain article info Article history: Received 11 June 2009 Received in revised form 27 October 2009 Accepted 29 October 2009 Keywords: Aquaporins Brassica oleracea High temperature Osmotic water permeability Plasma membrane fluidity abstract The effect of high root temperature on the water-uptake capability of broccoli plants (Brassica oleracea cv. Parthenon), the status of the plasma membrane and the role of aquaporins in water transport through the plant plasma membrane were investigated. For this, different temperatures (25, 35, 40 and 45 ◦ C) were assayed. A decrease of the PIP1 and PIP2 aquaporins abundance with increasing temperature was observed, but the P f values of protoplasts increased with the temperature. Changes of membrane fluidity were shown only at 40 ◦ C, driving the membrane to a more rigid state. Also, the damaging effects of the stress, determined as electrolyte leakage (EL) in the whole root, and the possible osmotic adjustment, as an adaptive mechanism, were investigated. We propose that the increase in osmotic water permeability at higher temperature was not due to changes in the abundance of PIPs, but was probably due to an increase of permeability through the lipid bilayer. Also, the relation of the reduced gas exchange and aquaporins would provide a possible signal mechanism for acclimation to heat stress. © 2009 Elsevier B.V. All rights reserved. 1. Introduction It has been estimated that the global mean temperature will rise 0.2 ◦ C per decade in the coming years, according to a report of the Intergovernmental Panel on Climatic Change (IPCC) (IPCC Expert Meeting Report, 2007). This may alter the geographical distribu- tion and growing season of agricultural crops (Porter, 2005). It is known that high temperature is an important factor affecting crop production worldwide. Heat stress is defined as the rise in temperature beyond a thresh- old level for a period of time sufficient to cause irreversible damage to plant growth and development. In general, a transient eleva- tion in temperature, usually 10–15 ◦ C above ambient, is considered heat shock or heat stress (Wahid et al., 2007). Also, heat tolerance is defined generally as the ability of a plant to grow and produce economic yield under high temperatures (Singh et al., 2007). The response of plants to heat stress includes morphological alterations (Giaveno and Ferrero, 2003) and anatomical modifications (Zhang et al., 2005), as well as physiological and biochemical changes. Concerning plant physiological responses, the following have been reported: changes in water relations (Simoes-Araujo et al., 2003; Abbreviations: BSA, bovine serum albumin; DPH, 1,6-diphenyl-1,3,5-hexatriene; DTT, dithiothreitol; P f , osmotic water permeability; PVP, polyvinylpyrrolidone. ∗ Corresponding author. Tel.: +34 968 396310; fax: +34 968 396213. E-mail address: mcarvaja@cebas.csic.es (M. Carvajal). Morales et al., 2003; Caba ˜ nero et al., 2004), accumulation of com- patible osmolytes (Hare et al., 1998; Sakamoto and Murata, 2002), decrease in photosynthesis (Sharkova, 2001; Wise et al., 2004), hormonal changes (Maestri et al., 2002) and cell membrane ther- mostability (Martineau et al., 1979; Somerville and Browse, 1991). At the molecular level, alteration of gene expression and accu- mulation of transcripts, as a stress-tolerance strategy, have been observed (Iba, 2002; Xu et al., 2008). In order to cope with heat stress, plants develop several mech- anisms, including maintenance of membrane stability. Thus, many changes occur in the plasma membrane during the acclimation process, such as alterations in the lipid and polypeptide compo- sitions and fluidity (Pareek et al., 1997; Uemura et al., 1995) and in the permeability (Zhang et al., 2005). High root temperatures have been reported to produce changes in the plasma membrane fluidity (Carvajal et al., 1996; Liu and Huang, 2004), modify its fatty acid composition (Borochovneori and Shani, 1995; Behl et al., 1996; Wang and Hsin, 2006), cause leakage of ions and amino acids (Yang et al., 2005; Lyons et al., 2007) and affect the activity of some pro- teins, such as ATPase (Lindberg et al., 2005). Temperature has an important role in plant water relations. It has been described how supra-optimal root zone temperatures induced shoot water deficit in pepper, by altering the balance between root water uptake and water loss from the shoots (Dodd et al., 2000). It is known that high temperatures may induce varia- tions in the mesophyll internal conductance (Bernacchi et al., 2002) and may affect osmotic adjustment in plants due to the increase of 0098-8472/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2009.10.007