The efficiency of electron transfer from QA−to the donor side of Photosystem II decreases during induction of photosynthesis: Evidences from chlorophyll fluorescence and photoacoustic techniques
✍ Scribed by Nikolai G. Bukhov; Robert Carpentier
- Publisher
- Springer
- Year
- 1996
- Tongue
- English
- Weight
- 681 KB
- Volume
- 47
- Category
- Article
- ISSN
- 0166-8595
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✦ Synopsis
The amplitudes ratio of the fast and slow phases (Afast/Aslow) in the kinetics of the dark relaxation of variable chlorophyll fluorescence (Fv) was studied after various periods of illumination of dark-adapted primary barley leaves. Simultaneously, photosynthetic activity was monitored using the photoacoustic technique and the photochemical and non-photochemical fluorescence quenching parameters. The ratio Afast/Aslow changed with the preceding illumination time in a two-step manner. During the first stage of photosynthetic induction (0--20 s of illumination), characterized by a drop in O2-dependent photoacoustic signal following an initial spike and by a relatively stable small value of photochemical Fv quenching, the ratio Afast/Aslow remained practically unaltered. During the second stage (20-60 s of illumination), when both the rate of 02 evolution and the photochemical Fv quenching were found to be sharply developed, a marked increase in the above ratio was also observed. A linear correlation was found between the value of the photochemical quenching and the ratio Afast/Aslow during the second phase of photosynthetic induction. It is concluded that the slow phase appearing in the kinetics of Fv dark relaxation is not due to the existence of Photosystem II reaction centres lacking the ability to reduce P700 + with high rates, but is instead related to the limitation of electron release from Photosystem I during the initial stage of the induction period of photosynthesis. This limitation keeps the intersystem electron carriers in the reduced state and thus increases the probability of back electron transfer from QA to the donor side of Photosystem II.
Abbreviations: Afast/Aslow -the ratio of magnitudes between the fast and slow phases of dark relaxation of variable fluorescence; Fo-initial level of chlorophyll fluorescence; Fv-variable chlorophyll fluorescence (F -Fo); (Fv)s-the yield of variable chlorophyll fluorescence under saturating pulse in illuminated leaves; (Fv)M-the yield of variable chlorophyll fluorescence under saturating pulse in dark-adapted leaves; PA-photoacoustic; PS I -Photosystem I; PS II-Photosystem II; q N -non-photochemical quenching; qQ-photochemical quenching