期刊
PHOTOSYNTHESIS RESEARCH
卷 129, 期 3, 页码 279-290出版社
SPRINGER
DOI: 10.1007/s11120-016-0267-5
关键词
Cyclic electron flow; Electron sink; Mehlerascorbate peroxidase (MAP)-pathway; Oxygen; Photosystem I; Photorespiration; P700
资金
- Japan Society for the Promotion of Science [21570041]
- Grants-in-Aid for Scientific Research [16H06379, 21570041] Funding Source: KAKEN
To elucidate the molecular mechanism to oxidize the reaction center chlorophyll, P700, in PSI, we researched the effects of partial pressure of O-2 (pO(2)) on photosynthetic characteristic parameters in sunflower (Helianthus annuus L.) leaves. Under low CO2 conditions, the oxidation of P700 was stimulated; however the decrease in pO(2) suppressed its oxidation. Electron fluxes in PSII [Y(II)] and PSI [Y(I)] showed pO(2)-dependence at low CO2 conditions. H+-consumption rate, estimated from Y(II) and CO2-fixation/photorespiration rates (JgH(+)), showed the positive curvature relationship with the dissipation rate of electrochromic shift signal (V (H) (+) ), which indicates H+-efflux rate from lumen to stroma in chloroplasts. Therefore, these electron fluxes contained, besides CO2-fixation/photorespiration-dependent electron fluxes, non-H+-consumption electron fluxes including Mehler-ascorbate peroxidase (MAP)-pathway. Y(I) that was larger than Y(II) surely implies the functioning of cyclic electron flow (CEF). Both MAP-pathway and CEF were suppressed at lower pO(2), with plastoquinone-pool reduced. That is, photorespiration prepares the redox-poise of photosynthetic electron transport system for CEF activity as an electron sink. Excess Y(II), [Delta Y(II)] giving the curvature relationship with V (H) (+) , and excess Y(I) [Delta CEF] giving the difference between Y(I) and Y(II) were used as an indicator of MAP-pathway and CEF activity, respectively. Although Delta Y(II) was negligible and did not show positive relationship to the oxidation-state of P700, Delta CEF showed positive linear relationship to the oxidation-state of P700. These facts indicate that CEF cooperatively with photorespiration regulates the redox-state of P700 to suppress the over-reduction in PSI under environmental stress conditions.
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