BIOLOGIA PLANTARUM 51 (2): 372-376, 2007 372 BRIEF COMMUNICATION Methyl salicylate fumigation increases monoterpene emission rates J. PEÑUELAS 1 , J. LLUSIÀ, and I. FILELLA Unitat d’Ecofisiologia CSIC-CEAB-CREAF, Centre de Recerca Ecològica i Aplicacions Forestals, Edifici C, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain Abstract We aimed to assess the potential effects of fumigation by methyl salicylate (MeSA) on plant monoterpene production and emissions. We evaluated monoterpene production and emissions both by chromatographic and proton transfer reaction mass spectrometry at the whole plant- and leaf-scales, in MeSa-fumigated (ca. 60 mm 3 m -3 in air) and control (without MeSa fumigation) holm oak (Quercus ilex L.) plants exposed to temperatures ranging from 25 to 50 ºC. The MeSa-fumigated plants showed ca. 3 - 4-fold greater leaf monoterpene concentrations and emission rates than the control plants between the temperatures of 25 to 45 ºC. Additional key words: antioxidants, limonene, β-myrcene, α-pinene, β-pinene, PTR-MS, Quercus ilex, thermotolerance. ⎯⎯⎯⎯ Methyl salicylate (MeSA) is known to be released by stressed plants. It is considered to be a signal involved in eliciting plant resistance to stressors such as chilling (Ding et al. 2002, Fung et al. 2004), salinity (Borsani et al. 2001), drought (Munné-Bosch and Peñuelas 2003), heat (Clarke et al. 2004), and the gall midge Dasineura marginemtorquens in the willow (Ollerstam and Larsson 2003). It is also known that plants respond to biotic and abiotic stresses by emitting terpenes, a fact that seem to serve diverse physiological and ecological functions including possible thermotolerance enhan-cement (Peñuelas and Llusià 2001, 2002, 2003, 2004). Fumigation with isoprene (10 cm 3 m -3 ) has been found to confer thermotolerance on Quercus ilex seedlings and at the same time to suppress the activation of antioxidants in the leaf. Among these changes, mono- terpene production and emission have been found to be reduced by 70 % (Peñuelas et al. 2005a). In another study, no clear thermotolerance or consistent changes in the emission of other monoterpenes occurred in response to limonene fumigation (7.5 cm 3 m -3 ) (Llusià et al. 2005a). Finally, in a recent study, MeSA fumigation (60 mm 3 m -3 ) was found to cause sustained accumulation of MeSA in leaves, reduced antioxidant levels (ascorbate and tocopherol) and increased oxidative damage in the holm oak at temperatures ranging from 25 to 50 ºC (Llusià et al. 2005b). We aimed to answer the question whether or not this decreased thermotolerance and anti- oxidant performance in response to the sustained accumulation of MeSA produced by MeSa fumigation would be accompanied by any increase in monoterpene production and emission. If this was the case, we would have another indication that airborne MeSA may activate this monoterpene response just as it does with the expression of defense-related or stress-related genes in other plants (Shulaev et al. 1997, Fung et al. 2004). We studied the above-mentioned question in Quercus ilex L., a dominant Mediterranean forest species (Rodà et al. 1999) whose leaves may suffer from thermal stress at temperature above 35 ºC (Larcher 2000, Peñuelas et al. 1998). Usually, CO 2 uptake suddenly decreases at temperature between 40 and 50 ºC, although Q. ilex grows in sites where maximum air temperatures reach this range (e.g. Seville, Southern Spain). We exposed Q. ilex seedlings to temperature increases from 25 to 50 ºC in 5 ºC steps in atmospheres fumigated with MeSA (ca. 60 mm 3 m -3 ). This represents a high air MeSA concentration, but it is only twice the concentration described in air surrounding tomato plants (Deng et al. 2004) and is much lower than the 100 cm 3 m -3 used in studies of gene expression enhancement by MeSa (Fung et al. 2004). ⎯⎯⎯⎯ Received 16 August 2005, accepted 27 April 2006. Abbreviations: MeSA - methyl salicylate; PTR-MS - proton transfer reaction mass spectrometry. Acknowledgements: This research was partly supported by Spanish MCYT grants CGL2004-01402/BOS and CGL2006-04025/BOS. We also gratefully acknowledge the partial funding from the ISONET European Commission contract MC-RTN-CT-2003-504720 1 Corresponding author; fax: (+34) 93 5814151; e-mail: josep.penuelas@uab.cat