Behnke, K.K.BehnkeGhirardo, A.A.GhirardoJanz, D.D.JanzKanawati, B.B.KanawatiEsperschütz, J.J.EsperschützZimmer, I.I.ZimmerSchmitt-Kopplin, P.P.Schmitt-KopplinNiinemets, Ü.Ü.NiinemetsPolle, A.A.PolleSchnitzler, J. P.J. P.SchnitzlerRosenkranz, M.M.Rosenkranz2017-09-072017-09-072013https://resolver.sub.uni-goettingen.de/purl?gro-2/4837In the present study, biogenic volatile organic compound (BVOC) emissions and photosynthetic gas exchange of salt-sensitive (Populus x canescens (Aiton) Sm.) and salt-tolerant (Populus euphratica Oliv.) isoprene-emitting and non-isoprene-emitting poplars were examined under controlled high-salinity and high-temperature and -light episode (‘sunfleck’) treatments. Combined treatment with salt and sunflecks led to an increased isoprene emission capacity in both poplar species, although the photosynthetic performance of P. × canescens was reduced. Indeed, different allocations of isoprene precursors between the cytosol and the chloroplast in the two species were uncovered by means of 13CO2 labeling. Populus × canescens leaves, moreover, increased their use of ‘alternative’ carbon (C) sources in comparison with recently fixed C for isoprene biosynthesis under salinity. Our studies show, however, that isoprene itself does not have a function in poplar survival under salt stress: the non-isoprene-emitting leaves showed only a slightly decreased photosynthetic performance compared with wild type under salt treatment. Lipid composition analysis revealed differences in the double bond index between the isoprene-emitting and non-isoprene-emitting poplars. Four clear metabolomics patterns were recognized, reflecting systemic changes in flavonoids, sterols and C fixation metabolites due to the lack/presence of isoprene and the absence/presence of salt stress. The studies were complemented by long-term temperature stress experiments, which revealed the thermotolerance role of isoprene as the non-isoprene-emitting leaves collapsed under high temperature, releasing a burst of BVOCs. Engineered plants with a low isoprene emission potential might therefore not be capable of resisting high-temperature episodes.enjournal_article10.1093/treephys/tpt0183147205