Leaf PPDK activation state in WT and T27 leaves as a function of increasing irradiance. PPDK enzyme activity was measured in leaf extracts from leaves that had first been dark adapted for 30 min and then illuminated for 15 min at the designated irradiance level. Data points for T27 leaves at 100 and 1,200 μmol quanta m⁻²s⁻¹ were omitted due to insufficient number of replicates. Values shown are the means ± se, n = 3. Differences between genotypes for data points 600, 800, 1,000, and 1,600 μmol quanta m⁻² s⁻¹ are not significant (P > 0.05, two-tailed Student’s t test).