Fig. 3

Effect of exogenous Ca²⁺ on chlorophyll fluorescence parameters and images in leaves of cucumber under normoxic conditions (a), hypoxic treatments (b) and hypoxia + Ca²⁺ treatments (c). Values are means ± SE of three independent experiments. Bars marked with dissimilar letters are significantly different from each other according to Duncan’s multiple range tests (p < 0.05). Image of Fv/Fm, ΦPSII, qP and NPQ (=Fm/Fm′-1) with actinic illumination of 450 μmol photons m^− 2 s^− 1 are shown. Fv/Fm, the maximum quantum yield of PSII; ΦPSII, actual photochemical efficiency of PSII; qP, photochemical quenching coefficient; NPQ (=Fm/Fm′-1), non-photochemical quenching coefficient. Each image in the same column represents the same leaf. The color scale at the top indicates values from 0 (black) to 1 (pink)