Suppression of flash-induced PSII-dependent electrogenesis caused by proton pumping in chloroplasts

Abstract

Suppression of fla,sh-induced PSD-dependent electrogenesis caused hy proton pumping in chloroplasts, -Physio], Plant, 98: 156-164,Pre-illumination of the thyiakoid membrane of Peperomia meiallica chloropiasts leads to a reversible suppression of the flash-induced electrical potential as measured either with the eiectrochromic bandshift (P515), microclectrode impalement or patchclamp technique. The energization-dependent potential suppression was nol obseived in the presence of 1 uM nigericin suggesting tiie involvement of proton and/or cation gradients. Energization in the presence of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (;DCMU) and N,,N,N',N'-tetramethylphenylenediamine (TMPD), i,e, cyclic electron flow around photosystem (PS) 1, results in the accumulation of TMPD* in the thyiakoid lumen. The reversible suppression of the flash-induced tnembrane potential was nol observed in these conditions indicating that it is nol a general cation-induced increase of membrane capacitance. Cyclic electron flow around PSI in the presence of DCMU and phenazine methosulfate (PMS) results in the accumulation of P,MS' and H* in the thyiakoid lumen. The absence of reversible suppression of the flash-induced membrane potential for this condition shows that accumulation of protons does not lead to (I) a reversible increase of memhrane capacitance and (2) a reversible suppression of PSI-dependent electrogenesis. Reversible inactivation of PSIl by a low pH in the thyiakoid lumen is therefore proposed to be the cause for the lemporaiy suppression of the flash-induced electrical potential. The flash-induced PSII-dependent membrane potential, as measured after major oxidation of P700 in fai-red background light, was indeed found to be suppressed at low assay pH (pH 5) in isolated spinach {Spinacia oleracea} chioroplasts.