The e.s.r. spectra of chloroplasts at the temperature of liquid nitrogen after illumination of the frozen samples have been studied. It was found that the intensity and width of the e.s.r. signal depend on the presence of inorganic phosphate (Pinorg). It was established that in the chloroplasts impoverished in the content of endogeneous Pinorg the amplitude of the e.s.r. signal I rises and its width increases; addition of phosphate, the electron donor for photosystem II (diphenylcarbazide) or diurone before freezing the chloroplasts returns these parameters to the usual values. It is shown that the curve of u.h.f.-saturation of the e.s.r. I signal of the chloroplasts without Pinorg differs from that for normal chloroplasts but matches it after adding Pinorg or diurone. It is concluded that in the absence in the chloroplasts of inorganic phosphate the influx of electrons to P680+ centres is disturbed and the cation-radical of chlorophyll P680 formed on illumination contributes to the narrow e.s.r. signal (ΔHmax ∼- 0 · 87 mTl). From comparison of the differential e.s.r. spectrum in the chloroplasts with the known e.s.r. signal of the phosphate anion-radical it is assumed that the phosphate ion may be an endogenous electron donor for P680+.
|Number of pages||5|
|Publication status||Published - Dec 1 1991|
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