Assessment of the impact of photosystem I chlorophyll fluorescence on the pulse-amplitude modulated quenching analysis in leaves of Arabidopsis thaliana
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© Springer Science+Business Media 2015. In their natural environment, plants are exposed to varying light conditions, which can lead to a build-up of excitation energy in photosystem (PS) II. Non-photochemical quenching (NPQ) is the primary defence mechanism employed to dissipate this excess energy. Recently, we developed a fluorescence-quenching analysis procedure that enables the protective effectiveness of NPQ in intact Arabidopsis leaves to be determined. However, pulse-amplitude modulation measurements do not currently allow distinguishing between PSII and PSI fluorescence levels. Failure to account for PSI contribution is suggested to lead to inaccurate measurements of NPQ and, particularly, maximum PSII yield (Fv/Fm). Recently, Pfündel et al. (Photosynth Res 114:189-206, 2013) proposed a method that takes into account PSI contribution in the measurements of Fo fluorescence level. However, when PSI contribution was assumed to be constant throughout the induction of NPQ, we observed lower values of the measured minimum fluorescence level (Fo′ calc.) than those calculated according to the formula of Oxborough and Baker (Photosynth Res 54:135-142 1997) (Fo′ calc.), regardless of the light intensity. Therefore, in this work, we propose a refined model to correct for the presence of PSI fluorescence, which takes into account the previously observed NPQ in PSI. This method efficiently resolves the discrepancies between measured and calculated Fo′ produced by assuming a constant PSI fluorescence contribution, whilst allowing for the correction of the maximum PSII yield.