Studies on the induction of chlorophyll fluorescence in isolated barley protoplasts. IV. Resolution of non-photochemical quenching

Abstract Using DCMU addition and light-saturation pulses, chlorophyll fluorescence quenching by isolated barley protoplasts has been examined upon illumination with different light intensities. Total quenching was constant at all intensities, photochemical quenching predominating in low light and non-photochemical quenching becoming increasingly important at higher intensity. The components of non-photochemical quenching were resolved by examination of kinetics of relaxation of quenching upon DCMU addition or darkening. It was found that: (a) energy-dependent quenching saturated with characteristics similar to photosynthesis; (b) a slowly relaxing, NaF-sensitive component attributed to protein phosphorylation saturated in low light and decreased at high light; (c) an irreversible component ascribed to photoinhibition was a major quencher as light levels were increased above saturation; (d) the decreased photochemical quenching at high light was not strictly correlated with alteration in rate of O2 evolution. Analysis of these data showed that the quantum yield of Photosystem II declined as the light intensity was increased from zero to that saturating for photosynthesis and was associated with the presence of energy-dependent quenching. The regulation of excitation dissipation by the thylakoid membrane is discussed.

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