Cyclic electron flow within PSII functions in intact chloroplasts from spinach [Spinacia oleracea] leaves

• Published in: Plant and cell physiology 2002-08, Vol.43 (8), p.951-957
• Main Authors: "Miyake, C. (Kyushu Univ., Fukuoka (Japan)), Yonekura, K, Kobayashi, Y, Yokota, A.
• Format: Article
• Language: English
• Subjects: a pH gradient across thylakoid membranes; AEF; alternative electron flow; APX; Asc; Asc peroxidase; ascorbate; BIOCHEMICAL PATHWAYS; CEF-PSII; Chlorophyll - metabolism; CHLOROPLASTS; Chloroplasts - drug effects; Chloroplasts - metabolism; Chloroplasts - radiation effects; cyclic electron flow within PSII; defined as (F′m–Fs)/F′m; defined as Fm/Fm′–1; Electron Transport - drug effects; Electron Transport - radiation effects; Fm; Fm after illumination; Hydrogen-Ion Concentration; Ionophores - pharmacology; Je(PSII); Keywords: Alternative electron flow — Chloroplasts — Cyclic electron flow — Photoinhibition — PSII — Water–water cycle; LEAVES; Light; Light-Harvesting Protein Complexes; maximal yield of Chl fluorescence after dark adaptation; MDA; minimal Chl fluorescence after dark adaptation; monodehydroascorbate radical; Nigericin - pharmacology; non-photochemical quenching coefficient of Chl fluorescence; NPQ; Oxygen - metabolism; PCO cycle; PCR cycle; PFD; photorespiratory carbon-oxidation cycle; Photosynthesis - drug effects; Photosynthesis - physiology; Photosynthesis - radiation effects; photosynthetic carbon-reduction cycle; Photosynthetic Reaction Center Complex Proteins - drug effects; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosynthetic Reaction Center Complex Proteins - radiation effects; photosynthetically active photon flux density; PHOTOSYSTEMS; Plant Leaves - drug effects; Plant Leaves - metabolism; Plant Leaves - radiation effects; plastoquinol; plastoquinone; PQH2; SOD; SPINACIA OLERACEA; Spinacia oleracea - drug effects; Spinacia oleracea - metabolism; Spinacia oleracea - radiation effects; superoxide dismutase; the electron flux in PSII; the molar ratio of PSII to PSI in thylakoid membranes; the quantum yield of electron transport in PSII at steady state; the rate of O2 uptake; the water–water cycle; V(O2); Water - pharmacology; Water - physiology; WWC; yield of steady-state Chl fluorescence; ΔpH; Φ(PSII)
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pcf113

"Using thylakoid membranes, we previously demon strated that accumulated electrons in the photosynthetic electron transport system induces the electron flow from the acceptor side of PSII to its donor side only in the presence of a pH gradient (DpH) across the thylakoid membranes. This electron flow has been referred to as cyclic electron flow within PSII (CEF-PSII) [Miyake and Yokota (2001) Plant Cell Physiol. 42: 508]. In the present study, we examined whether CEF-PSII operates in isolated intact chloroplasts from spinach leaves, by correlating the quantum yield of PSII [F(PSII)] with the activity of the linear electron flow [V(O sub2)j. The addition of the protonophore nigericin to the intact chloroplasts decreased F(PSII), but increased V(O sub2), and relative electron flux in PSII (F(PSII) * PFD and V(O sub2) were proportional to one another. F(PSII) * PFD at a given V(O sub2) was much higher in the presence of ApH than that in its absence. These effects of nigericin on the relationship between F(PSII) * PFD and V(O sub2) are consistent with those previously observed in thyl-akoid membranes, indicating the occurrence of CEF-PSII also in intact chloroplasts. In the presence of DpH, CEF-PSII accounted for the excess electron flux in PSII that could not be attributed to photosynthetic linear electron flow. The activity of CEF-PSII increased with increased light intensity and almost corresponded to that of the water-water cycle (WWC), implying that CEF-PSII can dissipate excess photon energy in cooperation with WWC to protect PSII from photoinhibition under limited photo-synthesis conditions"