Figure 1.

Time course of the net photosynthetic O₂ evolution of leaf discs of PqR (▵) and PqS (○) biotypes of E. canadensis (in percentage of untreated control) in the presence of 0.5 mm Pq at a PPFD of 850 μmol m⁻² s⁻¹ (untreated leaves of the PqS and PqR biotypes evolved 53 ± 6 and 55 ± 5 μmol O₂ mg⁻¹ chlorophyll h⁻¹, respectively). Pq was applied under dim-light (15 μmol m⁻² s⁻¹) and the treated leaves were then kept in the dark for 10 min to allow the surface of the leaves to become dry before any illumination. The measurement of O₂ evolution was carried out in a leaf disc electrode and the linear rate of O₂ evolution corrected for dark respiration was used to calculate the light-dependent O₂ evolution or O₂ consumption. The data are means of six replicates and se are shown when larger than the symbols.