Evidence That Light, Carbon Dioxide, and Oxygen Dependencies of Leaf Isoprene Emission Are Driven by Energy Status in Hybrid Aspen

Abstract

Leaf isoprene emission scales positively with light intensity, is inhibited by high carbon dioxide (CO 2 ) concentrations, and may be enhanced or inhibited by low oxygen (O 2 ) concentrations, but the mechanisms of environmental regulation of isoprene emission are still not fully understood. Emission controls by isoprene synthase, availability of carbon intermediates, or energetic cofactors have been suggested previously. In this study, we asked whether the short-term (tens of minutes) environmental control of isoprene synthesis results from alterations in the immediate isoprene precursor dimethylallyldiphosphate (DMADP) pool size, and to what extent DMADP concentrations are affected by the supply of carbon and energetic metabolites. A novel in vivo method based on postillumination isoprene release was employed to measure the pool size of DMADP simultaneously with the rates of isoprene emission and net assimilation at different light intensities and CO 2 and O 2 concentrations. Both net assimilation and isoprene emission rates increased hyperbolically with light intensity. The photosynthetic response to CO 2 concentration was also hyperbolic, while the CO 2 response curve of isoprene emission exhibited a maximum at close to CO 2 compensation point. Low O 2 positively affected both net assimilation and isoprene emission. In all cases, the variation in isoprene emission was matched with changes in DMADP pool size. The results of these experiments suggest that DMADP pool size controls the response of isoprene emission to light intensity and to CO 2 and O 2 concentrations and that the pool size is determined by the level of energetic metabolites generated in photosynthesis.

Bisphosphonate Inhibitors Reveal a Large Elasticity of Plastidic Isoprenoid Synthesis Pathway in Isoprene-Emitting Hybrid Aspen

“…As accumulation of the pathway intermediates does occur in vivo under different environmental conditions Rasulov et al, 2011Rasulov et al, , 2014Li and Sharkey, 2013a), in dependence on leaf ontogeny (Rasulov et al, 2014), and across genotypes varying in constitutive activity of DXP synthase , we argue that accumulation of phosphorylated intermediates provides a key way for fine tuning of pathway flux by regulation of energy supply. Such a possibility for regulation of isoprene synthesis has been postulated (Niinemets et al, 1999;Rasulov et al, 2009b), but a physiological explanation has been lacking so far. In addition, the study also provides evidence of a certain cooperativity of the plastidic and cytosolic isoprenoid pathways.…”

“…The experiments were conducted with 1-year-old saplings of hybrid aspen (Populus tremula 3 Populus tremuloides) clone H200 grown in 4-L pots filled with sand and commercial potting soil under optimal supply of water and nutrients as in our previous studies (Rasulov et al, 2009b(Rasulov et al, , 2011. The growth conditions were kept constant in a Percival plant growth chamber (CLF Plant Climatics GmbH).…”

Monoterpene and sesquiterpene emissions from <i>Quercus coccifera</i> exhibit interacting responses to light and temperature

“…Based on recent investigations of the metabolic control of isoprene emissions by Rasulov et al (2009Rasulov et al ( , 2010 we hypothesized that at temperatures supraoptimal for photosynthetic processes MT biosynthesis in Q. coccifera leaves could be mostly limited by the availability of isoprenoid precursors produced from photosynthates. Accordingly, we expected that light saturation of MT emissions occurs earlier in the light response at 37 • C than in the light response at 30 • C, and that T m occurs earlier in the temperature response at 150 µmol m −2 s −1 PPFD than in the temperature response at 1000 µmol m −2 s −1 PPFD.…”

“…It is generally recognized that monoterpenes in BVOC non-storing plants are produced in the methylerythritol-phosphate (MEP) pathway located in chloroplasts, where photosynthetic processes provide the major bulk of primary carbon substrate and co-factors for the biosynthesis of isoprenoid precursors thus shaping the light responses of emissions (Loreto et al, 1996;Niinemets et al, 2002;Rasulov et al, 2009). Light activation of some enzymes in the MEP pathway might further contribute to positive light effects on emissions especially in the longer term control (Rasulov et al, 2009;Rivasseau et al, 2009;Schnitzler et al, 2010). Light dependency is more uncertain for SQT emissions, whose biosynthesis are thought to proceed in the cytosol.…”

Estimations of isoprenoid emission capacity from enclosure studies: measurements, data processing, quality and standardized measurement protocols

“…For non-induced leaves, for instance after prolonged darkening, biochemical induction of photosynthesis and monoterpene (Noe et al, 2010) and isoprene (Rasulov et al, 2009b) emissions may take 20-30 min (Niinemets et al, 2010c for a review). Such non-specific storage effects and induction responses can be monitored by fast online BVOC detector systems and reaching a steadystate emission rate can be appropriately estimated.…”