Figure 1.

Effect of bicarbonate on the amplitude of ΔF in Mn-restored PSII membrane fragments. The membranes (DT-20) were depleted of Mn by washing in 1 M Tris⋅HCl/0.5 M MgCl₂ (17). The fragments were then suspended in media at different pH before (curves 5) and after (curves 1–4) addition of MnCl₂ at 0.1 μM (2 Mn/RC) (A) or 0.2 μM (4 Mn/RC) (B). For curves 1 and 2, the PSII membranes were suspended in non-bicarbonate-depleted medium. ΔF was measured before (curves 1) and after (curves 2) addition of 0.4 mM NaHCO₃. For curves 3 and 4, the membranes were placed in bicarbonate-depleted medium. ΔF was measured before (curves 3) and after (curves 4) addition of 0.4 mM NaHCO₃. [Chl] = 10 μg/ml; 20°C. The value of photoinduced ΔF in untreated preparations at a given pH is taken as 100%.