Fig. 5.

Temperature dependence of the rate constant of isoprene synthase (k) in hybrid aspen grown under control (day/night temperature 25/20 °C) and high temperature (35/27 °C) conditions. The first order reaction rate constant was estimated as the slope of the linear part of dimethylallyl diphosphate pool size vs. isoprene emission rate relationship through the dark decay of isoprene emission and corresponds to the environmental conditions (ambient CO₂ concentration of 360 μmol mol^-1, O₂ concentration of 21% and incident quantum flux density of 650 μmol m^-2 s^-1) prior to leaf darkening. The number of replicates and data presentation as in Fig. 2. The activation energies for k (ΔH_a, kJ mol^-1, Eq. 3) are also demonstrated (P < 0.001 for the difference among the treatments).