Effects of PsbP Knockdown on the Photosynthetic Electron Transfer in Nicotiana tabacum

Abstract

Transgenic tobacco plants deficient in PsbP (∆PsbP), one of the extrinsic proteins of pho-tosystem II (PSII), were characterized with respect to thylakoid functional properties. The ∆PsbP plants showed low PSII activity and the inhibition was located at the Mn-cluster in PSII. In addition , chlorophyll fluorescence and spectroscopic measurements indicated that the forward electron flow from Q A − to plastoquinone was hindered in ∆PsbP leaves; significant accumulation of Q A − was observed, while P700 in photosystem I (PSI) was noticeably oxidized. Consistent with this observation , thermoluminescence studies suggested the stabilization of the redox pair of S 2 Q A − in ∆PsbP leaves. We speculate that these properties of PSII in ∆PsbP leaves resemble an intermediate state of PSII biogenesis, which is almost inactive but relatively stable in thylakoid membranes. The function of PsbP is discussed in terms of the dynamic life cycle of PSII.