Figure 4.

Effects of willow leaf age on isoprene emission and isoprene synthase isoforms. A, Foliar isoprene emission as a function of nodal position (leaf age), average of duplicate samples. B, Leaf area as a function of nodal position, average of duplicate samples. Leaves from node 6 (YOUNG) and node 12 (MATURE) from different willow stems were then pooled. Foliar isoprene emission and total isoprene synthase activity for these pooled samples (of 10 g fresh weight) are portrayed in C. The percentages of total isoprene synthase activity in thylakoid-bound and soluble forms for these pooled samples are shown in D. Results shown in C and D are averages of three separate experiments performed on consecutive days. Leaf isoprene emission rates are shown for leaves at PAR of 100 μmol m⁻² s⁻¹. Additional experiments (not shown) utilized PAR of 1000 μmol m⁻² s−¹ and obtained a similar profile to A with increased emission rates. Further details are given in Methods.