Chlorophyll fluorescence transients in a barley mutant lacking Photosystem I

We have compared the properties of a mutant of barley lacking Photosystem I (viridis-zb ⁶³ ) with the corresponding wild type using modulated fluorescence measurements. The mutant showed two unexpected characteristics. Firstly, there was a slow decline in the fluorescence signal in the light which was dependent on the presence of O₂ at concentrations similar to that in air; 2% O₂ in N₂ had no effect. The observed decline was mainly due to an increase in the non-photochemical quenching. Secondly, in the absence of O₂, saturating light pulses caused a pronounced transient decrease in the fluorescence signal; a similar effect could also be observed in wild type plants when neither CO₂ nor O₂ was present.Abbreviations PPFD- photosynthetic photon flux density - q_N- non-photochemical quenching of chlorophyll fluorescence - q_p- photochemical quenching of chlorophyll fluorescence