Pam 2000 chlorophyll fluorometer

In vivo chlorophyll a fluorescence was measured using a PAM-2000 chlorophyll fluorometer (Heinz Walz, Effeltrich, Germany). Plants were dark-adapted for 30 min. First, the minimum chlorophyll fluorescence at open PSII centres in the dark (Fo) and under actinic light (Fo’) was determined using a weak, red measuring light (650 nm) with very low intensity (0.8 μmol m⁻² s⁻¹). Next, a saturating pulse of white light (3000 μmol m⁻² s⁻¹ for 800 ms) was applied to estimate the maximum chlorophyll fluorescence at closed PSII centres in the dark (Fm) and under actinic light (Fm’). The parameters of Fv/Fm, qP, qN, YII, NPQ, and Y(NPQ) were calculated as described in [44 (link)]. The build in the program for determination of induction curve and subsequently measured light curve (IC + LC) was used on whole leaves.

Chl content and the Chl a/b ratio were determined as described [21 ]. The maximal photochemical efficiency of PSII (Fv/Fm) was measured with a PAM-2000 chlorophyll fluorometer (Walz, Germany) as described [22 (link)].

Chlorophyll fluorescence was measured in attached leaves with a PAM-2000 chlorophyll fluorometer (Walz), as described in15 (link). The maximal quantum yield of PSII photochemistry was measured after a period of dark adaptation as Fv/Fm = (Fm-Fo)/Fm where Fo is the initial fluorescence level (measured with a weak, non-actinic red light) and Fm is the maximal fluorescence level (measured with a 800-ms pulse of saturating white light). The actual quantum yield of PSII photochemistry was measured in the light as ΔF/Fm’ = (Fm’-Fs)/Fm where Fs is the steady-state fluorescence level and Fm’ is the maximal fluorescence level. ΔF/Fm’ was measured in leaves adapted to different PFDs of white light.