Yamamoto, Hiroshi .
Stimulation of Cyclic Electron Flow around Photosystem I (CEF-PSI) by Overexpression of Ferredoxin in Transplastomic Tobacco enhances Non-Photochemical Quenching (NPQ) of Chlorophyll Fluorescence.
Recent studies indicated that under stressful conditions, CEF-PSI contributes to the formation of delta pH across the thylakoid membranes, and induces NPQ of Chl fluorescence to dissipate excess photon energy as heat. In CEF-PSI, electron flow from PSI to plastoquinone was proposed to be mediated by two enzymes; NADPH dehydrogenase and ferredoxin:quinone oxidoreductase (FQR). However, a molecular mechanism of CEF-PSI has not been fully understood. In this study, we tested the hypothesis that ferredoxin (Fd) limits the activity of CEF-PSI in vivo and that the relief of this limitation promotes the NPQ of Chl fluorescence. In transplastomic tobacco expressing Fd from Arabidopsis in its chloroplasts, the minimum yield of Chl fluorescence (Fo) was higher than in the wild type. Fo was suppressed to the wild-type level upon illumination with far-red light, implying that the transfer of electrons by FQR from the chloroplast stroma to plastoquinone was enhanced in transplastomic plants. The activity of CEF-PSI became higher in transplastomic than in wild-type plants under conditions limiting photosynthetic linear electron flow. Similarly, NPQ of Chl fluorescence was enhanced in transplastomic plants. On the other hand, pool sizes of the pigments of the xanthophyll cycle and the amounts of PsbS protein were the same in all plants. Furthermore, stimulation of CEF-PSI did not affect the rate of photosynthesis and growth of plants. All these results supported the hypothesis strongly. We conclude that breeding plants with an NPQ of Chl fluorescence increased by an enhancement of CEF-PSI activity might lead to improved tolerance for abiotic stresses, particularly under conditions of low light use efficiency.
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1 - Research Institute of Innovative Technology for the Earth, Plant Research Group, 9-2 Kizugawadai, Kizu-cho, Soraku-gun, Kyoto, 619-0292, JAPAN
cyclic electron transport
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM