For detailed effects of excessive Pi application on photosynthesis, we
also examined the PSI parameters [Y(I), Y(ND), and Y(NA)] and
H+-management within the chloroplasts [proton
motive force (pmf ), H+-conductance in
chloroplastic ATPase (gH+) and
H+-efflux rate in chloroplastic ATPase
(V H+)] in the plants grown
under low-Pi, control-Pi, and 3.0 mM Pi conditions. Y(I) indicates the
photochemical quenching in PSI, whereas Y(ND) and Y(NA) indicate the
photosynthetic electron transport limitation at the donor and acceptor
sides of PSI, respectively
(Klughammer
& Schreiber, 1994). Y(I) showed a response similar to Y(II) (Figure
S1a). Y(ND) decreased with increasing Ci levels both under low-Pi and
control-Pi conditions (Figure S1b). Y(ND) in the 3.0 mM Pi plants
decreased with an increase in Ci, but the values were higher than those
in the low-Pi and control-Pi plants (Figure S1b). Y(NA) increased with
increasing Ci in both low-Pi and control-Pi plants, but Y(NA) was higher
in the low-Pi plants than in the control-Pi plants (Figure S1c). In
contrast, the 3.0 mM Pi plants showed the highest Y(NA) at low Ci
levels, and Y(NA) was maintained at higher levels in the 3.0 mM-Pi
plants than in the control-Pi plants (Figure S1c). These results
indicated that the low-Pi plants reduced PSI at higher Ci with
photosynthesis limitation, but the 3.0 mM Pi plants caused a disturbance
in the redox-state of PSI, shifting PSI to a more reduced state, despite
the donor-side PET limitation in PSI.