The g = 2 doublet signal does not correlate with the multiline signal in Ca2+-depleted PSII

Abstract

We studied the correlation between the doublet signal and the multiline signal induced in Ca2+-depleted (low-pH treated) photosystem (PS) II membranes in order to clarify the origin of the doublet signal. By illuminating the Ca2+-depleted PS II in the S2 state in the presence of DCMU, the intensity of multiline decreases concomitant with the appearance of the doublet signal at g = 2. During the dark incubation at 0°, the doublet signal decayed by the charge recombination with QA- concomitant with the recovery of the multiline, although the doublet decay was the much faster process (t1/2~ 2min) as compare with the multiline recovery (t1/2~ 10min). On the other hand, long dark storage at 77K lead to the doublet decay without the recovery of the multiline. The apparent non-correlated behaviors found between the two signals indicate that these two signals arise from the different origin, and do not support the view that the interaction between YZ radical and manganese cluster is responsible for the doublet signal. The recombination between QA- and doublet species lead to a thermoluminescence band at 7° at pH 5.5. The peak position upshifted to be 17° at pH 7.0, presumably due to the pH dependent property change of YZ.