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WHOLE PLANT AND ECOPHYSIOLOGY

Postillumination Isoprene Emission: In Vivo Measurements of Dimethylallyldiphosphate Pool Size and Isoprene Synthase Kinetics in Aspen Leaves¹

Department of Plant Physiology, University of Tartu, 51010 Tartu, Estonia (B.R., A.L.); and Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Tartu 51014, Estonia (L.C., Ü.N.)

The control of foliar isoprene emission is shared between the activity of isoprene synthase, the terminal enzyme catalyzing isoprene formation from dimethylallyldiphosphate (DMADP), and the pool size of DMADP. Due to limited in vivo information of isoprene synthase kinetic characteristics and DMADP pool sizes, the relative importance of these controls is under debate. In this study, the phenomenon of postillumination isoprene release was employed to develop an in vivo method for estimation of the DMADP pool size and to determine isoprene synthase kinetic characteristics in hybrid aspen (Populus tremula x Populus tremuloides) leaves. The method is based on observations that after switching off the light, isoprene emission continues for 250 to 300 s and that the integral of the postillumination isoprene emission is strongly correlated with the isoprene emission rate before leaf darkening, thus quantitatively estimating the DMADP pool size associated with leaf isoprene emission. In vitro estimates demonstrated that overall leaf DMADP pool was very large, almost an order of magnitude larger than the in vivo pool. Yet, the difference between total DMADP pools in light and in darkness (light-dependent DMADP pool) was tightly correlated with the in vivo estimates of the DMADP pool size that is responsible for isoprene emission. Variation in in vivo DMADP pool size was obtained by varying light intensity and atmospheric CO₂ and O₂ concentrations. From these experiments, the in vivo kinetic constants of isoprene synthase were determined. In vivo isoprene synthase kinetic characteristics suggested that isoprene synthase mainly operates under substrate limitation and that short-term light, CO₂, and O₂ dependencies of isoprene emission result from variation in DMADP pool size rather than from modifications in isoprene synthase activity.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ülo Niinemets (ylo.niinemets{at}emu.ee).

www.plantphysiol.org/cgi/doi/10.1104/pp.108.133512

^* Corresponding author; e-mail ylo.niinemets{at}emu.ee.

Received December 1, 2008; accepted January 4, 2009; published January 7, 2009.

This article has been cited by other articles:

				B. Rasulov, K. Huve, M. Valbe, A. Laisk, and U. Niinemets Evidence That Light, Carbon Dioxide, and Oxygen Dependencies of Leaf Isoprene Emission Are Driven by Energy Status in Hybrid Aspen Plant Physiology, September 1, 2009; 151(1): 448 - 460. [Abstract] [Full Text] [PDF]