In photoinhibited photosystem II particles pheophytin photoreduction remains unimpaired

Abstract
Oxygen‐evolving photosystem II particles (DT 20) isolated from pea chloroplasts by digitonin‐Triton X‐100 fractionation were photoinhibited with 150 W·m−2white light, at 20°C under three conditions: aerobic, anaerobic and strongly reducing (Ehpoised to approx. −250 mV with dithionite). Hill reaction rate (H2O → BQ) and variable fluorescence (Fv) declined in parallel in all three cases with shortening half times: 30, 10 and 2.5 min, respectively. Light‐induced absorbance changes at 685 nm characteristic of reversible photoaccumulation of reduced pheophytin (Eh≈ −250 mV) remained essentially unchanged. We conclude that the three types of photoinhibitory treatment do not impair the separation of charges between chlorophyll P‐680 and pheophytin in the photosystem II reaction center.