Figure 4. The dependence of photoinhibition on the redox state of QA.
The redox state of the primary electron acceptor QA was assayed using the qL fluorescence parameter concurrently with photoinhibitory quenching qI at 100 (solid symbols), 300 (half filled symbols), and 500 μmol photons m−2s−1 (open symbols, mean ± s.d., n = 3). Plants were exposed to at least 10 min of actinic illumination prior to qL measurement, and qI measured after 10 min of dark relaxation. While the extent of qI varies between plants, the relative redox state of QA remains similar between all plants within each actinic light intensity.