Isoprene function in two contrasting poplars under salt and sunflecks

• Published in: Tree physiology Vol. 33; no. 6; pp. 562 - 578
• Main Authors: Behnke, K, Ghirardo, A, Janz, D, Kanawati, B, Esperschütz, J, Zimmer, I, Schmitt-Kopplin, P, Niinemets, Ü, Polle, A, Schnitzler, J P, Rosenkranz, M
• Format: Journal Article
• Language: English
• Published: Canada 01-06-2013
• Subjects: Butadienes - metabolism; Carbon - metabolism; Carbon Dioxide - metabolism; Flavonoids - genetics; Flavonoids - metabolism; Hemiterpenes - biosynthesis; Hemiterpenes - genetics; Hemiterpenes - metabolism; Hot Temperature; Metabolome - genetics; Pentanes - metabolism; Photosynthesis - genetics; Phytosterols - genetics; Phytosterols - metabolism; Plant Leaves - metabolism; Populus - genetics; Populus - metabolism; Salt-Tolerance - genetics; Salts - metabolism; Salts - pharmacology; Sodium Chloride - adverse effects; Sodium Chloride - metabolism; Species Specificity; Stress, Physiological - genetics; Sunlight; Trees - genetics; Trees - metabolism; Volatile Organic Compounds - metabolism; 13C labeling; lipids; salt; isoprene; thermotolerance; metabolomics; Populus euphratica; Populus × canescens
• ISSN: 0829-318X; 1758-4469
• DOI: 10.1093/treephys/tpt018

In 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 (13)CO2 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.