Alteration of Electron Flow around P₆₈₀: The Effect on Photoinhibition

Abstract

Inhibition of photosynthesis by excess visible light (photoinhibition (1)) has been implicated as a possible factor limiting plant productivity (2). Understanding the role of photoinhibition in the whole plant necessitates understanding the mechanism by which such photoinhibitory damage is induced. PSII is most affected by photoinhibitory treatment, the damage is observed as an inhibition of light-limited and light-saturated photosynthesis and a quenching of chl a_ fluorescence (1). At the molecular level PSII electron transport is also inhibited. The light-induced absorbance change at 320nm (ΔA₃₂₀) arising from the reduction of Q_A provides a quantitative measurement of PSII primary photochemistry and hence is an excellent gauge of photoinhibitory damage (3). In this study we compared ΔA₃₂₀, chl a fluorescence and O₂ evolution as methods to monitor photoinhibition in isolated spinach thylakoids.