The chloroplast thylakoid membrane system is a molecular conveyor belt
✍ Scribed by Critchley, Christa
- Publisher
- Springer Netherlands
- Year
- 1988
- Tongue
- English
- Weight
- 675 KB
- Volume
- 19
- Category
- Article
- ISSN
- 0167-8019
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✦ Synopsis
Light drives photosynthesis, but paradoxically light is also the most variable environmental factor influencing photosynthesis both qualitatively and quantitatively. The photosynthetic apparatus of higher plants is adaptable in the extreme, as exemplified by its capacity for acclimation to very bright sunny or deeply shaded conditions. It can also respond to rapid changes in light such as sunflecks. In this paper I offer a model that i) explains the thylakoid membrane organisation into grana stacks and stroma lamellae, ii) proposes a role for rapid D1 protein turnover and LHCII phosphorylation, and iii) suggests a mechanism for photoinhibition. I argue that the photosynthetic membrane system is dynamic in three dimensions, so much so that, in the light, it is in constant motion and operates in a manner somewhat analogous to a conveyor belt. D1 protein degradation is proposed to be the motor that drives this system. Photoinhibition is suggested to be due to the arrest of D1 protein turnover.
Abbreviations: D1 protein -photosystem II reaction centre protein, 32 kDa -rapidly turning over, herbicide, Qa binding protein, LHCII -light-harvesting chlorophyll a/b binding protein of PS II, PS II~ centres -PS II complete with LHCII located in grana stacks, Pre-PS II -PS II complexes consisting only of the 47, 43 kDa and D2 proteins, D2 -diffusely staining, reaction centre polypeptide, 34 kDa, ofPS II, CP43 -chlorophyll a binding protein, 43 kDa, of PSII, CP47 -chlorophyll a binding protein, 47 kDa, of PSII, PS IIfl centres -PS |I complex with newly inserted D1 protein but devoid of LHCII.