Poster: Photosynthesis
Abs #
316: Post-illumination reduction of chloroplast stroma as estimated by oxidation level of P700 under far-red light
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Presenter: |
Endo, Tsuyoshi , tuendo@kais.kyoto-u.ac.jp |
Authors | Endo, Tsuyoshi (A) Sato, Fumihiko (A) | | Affiliations: |
(A): Graduate School of Biostudies, Kyoto University
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To monitor over-reduction in stroma induced by photo-oxidative stress, we employed a simple non-destructive method to monitor redox state around photosystem I before and after high-light illumination based on the level of P700 oxidation by far-red light (FR). Oxidation level of P700 induced by FR illumination decreased during daytime and recovered at night in sun leaves of Desmodium paniculatum. The recovery in the dark of once decreased oxidation level of P700 proceeded slowly with a half recovery time of about 5 hours. This depression of FR-oxidizable P700 was probably due to cyclic electron donation to P700+ or charge recombination within PSI. In either case, stromal over-reduction induced by sunlight was the direct cause, since the depression of P700 oxidation under FR was reproduced by illumination with saturating white light to dark-adapted leaves. Simultaneous measurements of P700 redox and chlorophyll fluorescence showed that the depression of P700 oxidation under FR was associated with non-photochemical reduction of the plastoquinone, which may be involved in cyclic electron transport activity.
A light-stressed transformant of tobacco, in which chloroplastic NAD(P)H dehydrogenase (NDH) was insertionally destroyed, showed stronger depression of P700 oxidation under FR and higher rate of non-photochemical reduction of the plastoqinone pool than wild type control, confirming association of both phenomena.
The dark level of blue-green fluorescence from intact chloroplasts was distinctly increased by high-light stress, suggesting NADPH was accumulated in stroma by the high-light treatment. Possible effects on photosynthetic activity of over-reduction induced by high-light stress and their physiological relevance are discussed.
