2.7 Evaluation of P700 redox state in leaves of SV and SA
In order to monitor the photosynthetic electron flow through PSI during steady state photosynthesis in vivo , we estimated the redox state of P700 in the light by measuring oxidation of P700 within the leaf as absorbance changes at 830 minus 875 nm. P700 was oxidized to P700+ at different intensities of actinic light ranging from 0 to 1804 μmol m-2s-1 (ΔA) then reduced in the dark and finally oxidized to a maximum level of P700+ under far-red illumination to favor PSI photochemistry (ΔAmax; Klughammer and Schreiber, 1994; Zygadlo et al., 2005; Klughammer & Schreiber, 2008). The light dependence of the P700 oxidation ratio (ΔA/ΔAmax; Klughammer & Schreiber, 1994; Zygadlo et al., 2005; Klughammer & Schreiber, 2008; Dalcorso et al., 2008) was examined inSV and SA plants. The Far-red light (FR) intensity used was 102 μmol m-2 s-1 and a 100 ms saturation pulse (SP) of PPFD of 8000 μmol m-2s-1 was applied under background AL and FR.