High misses after odd flashes in oxygen evolution in thoroughly dark-adapted thylakoids from pea andChenopodium album
✍ Scribed by J. Dirk Naber; Jack J. S. Rensen; Govindjee
- Book ID
- 104622400
- Publisher
- Springer
- Year
- 1993
- Tongue
- English
- Weight
- 496 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0166-8595
No coin nor oath required. For personal study only.
✦ Synopsis
In Photosystem II (PS II), water is oxidized to molecular oxygen and plastoquinone is reduced to plastoquinol. The oxidation of water requires the accumulation of four oxidizing equivalents, through the so-called S-states of the oxygen evolving complex; the production of plastoquinol requires the accumulation of two reducing equivalents on a bound plastoquinone, QB' It has been generally believed that during the flash-induced transition of each of the S-states (S n ~ Sn+ 1, where n = 0, 1, 2 and 3), a certain small but equal firaction of the PS II reaction centers are unable to function and, thus, 'miss' being turned over. We used thoroughly darkadapted thylakoids from peas (Pisum sativum) and Chenopodium album (susceptible and resistant to atrazine) starting with 100% of the oxygen evolving complex in the S~ state. Thylakoids were illuminated with saturating flashes, providing a double hit parameter of about 0.07. Our experimental data on flashnumber dependent oscillations in the amount of oxygen per flash fit very well with a binary pattern of misses: 0, 0.2, 0, 0.4 during S o --~ S,, S 1 ----) 82, S 2 ~ 83 and S 3 ~ S O transitions. Addition of 2 mM ferricyanide appears to shift this pattern by one flash. These results are consistent with the 'bicycle' model recently proposed by V. P. Shinkarev and C. A. Wraight (Oxygen evolution in photosynthesis: From unicycle to bicycle, 1993, Proc Natl Acad Sci USA 90:1834-1838), where misses are due to the presence of P+ or Q2 among the various equilibrium states ofPS II centers.