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Published on January 7, 2009; 10.1104/pp.108.133512

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Received December 1, 2008
Accepted January 4, 2009

Postillumination isoprene emission: in vivo measurements of dimethylallyldiphosphate pool size and isoprene synthase kinetics in aspen leaves

Bahtijor Rasulov , Lucian Copolovici , Agu Laisk , and Ulo Niinemets *

Department of Plant Physiology, University of Tartu, Riia 23, 51010 Tartu, Estonia; Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 1, Tartu 51014, Estonia

* Corresponding author; email: ylo.niinemets{at}emu.ee.

The control on 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 the current study, the phenomenon of postillumination isoprene release was employed to develop an in vivo method for estimation of the DMADP pool size and determine isoprene synthase kinetic characteristics in hybrid aspen (Populus tremula L. x P. tremuloides Michx.) leaves. The method is based on observations that after switching off the light, isoprene emission continues for 250-300 s, and 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 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 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.




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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]


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