Photorespiration provides the chance of cyclic electron flow to operate for the redox-regulation of P700 in photosynthetic electron transport system of sunflower leaves

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• 作者：Daisuke Takagi ; Masaki Hashiguchi ; Takehiro Sejima ; Amane Makino…
• 关键词：Cyclic electron flow ; Electron sink ; Mehler ; ascorbate peroxidase (MAP) ; pathway ; Oxygen ; Photosystem I ; Photorespiration ; P700
• 刊名：Photosynthesis Research
• 出版年：2016
• 出版时间：September 2016
• 年：2016
• 卷：129
• 期：3
• 页码：279-290
• 全文大小：1,079 KB
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Life Sciences
  Plant Physiology
  
• 出版者：Springer Netherlands
• ISSN：1573-5079
• 卷排序：129

文摘

To elucidate the molecular mechanism to oxidize the reaction center chlorophyll, P700, in PSI, we researched the effects of partial pressure of O₂ (pO₂) on photosynthetic characteristic parameters in sunflower (Helianthus annuus L.) leaves. Under low CO₂ conditions, the oxidation of P700 was stimulated; however the decrease in pO₂ suppressed its oxidation. Electron fluxes in PSII [Y(II)] and PSI [Y(I)] showed pO₂-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 pO₂, 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), [ΔY(II)] giving the curvature relationship with V_H+, and excess Y(I) [ΔCEF] giving the difference between Y(I) and Y(II) were used as an indicator of MAP-pathway and CEF activity, respectively. Although ΔY(II) was negligible and did not show positive relationship to the oxidation-state of P700, ΔCEF 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.