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The Antarctic psychrophile, Chlamydomonas subcaudata, is deficient in state I–state II transitions
- Morgan-Kiss, Rachael M., Ivanov, Alexander G., Huner, Norman P.
- Planta 2002 v.214 no.3 pp. 435-445
- Chlamydomonas reinhardtii, anaerobic conditions, chlorophyll, cytochrome b, cytochrome f, electron transfer, electron transport chain, fluorescence, magnesium, photosystem I, photosystem II, polypeptides, red light, Antarctic region
- State I–State II transitions were monitored in vivo and in vitro in the Antarctic, psychrophillic, green alga, Chlamydomonas subcaudata, as changes in the low-temperature (77 K) chlorophyll fluorescence emission maxima at 722 nm (F₇₂₂) relative to 699 nm (F₆₉₉). As expected, the control mesophillic species, Chlamydomonas reinhardtii, was able to modulate the light energy distribution between photosystem II and photosystem I in response to exposure to four different conditions: (i) dark/anaerobic conditions, (ii) a change in Mg²⁺concentration, (iii) red light, and (iv) increased incubation temperature. This was correlated with the ability to phosphorylate both of its major light-harvesting polypeptides. In contrast, exposure of C. subcaudata to the same four conditions induced minimum alterations in the 77 K fluorescence emission spectra, which was correlated with the ability to phosphorylate only one of its major light-harvesting polypeptides. Thus, C. subcaudata appears to be deficient in the ability to undergo a State I–State II transition. Functionally, this is associated with alterations in the apparent redox status of the intersystem electron transport chain and with higher rates of photosystem I cyclic electron transport in the psychrophile than in the mesophile, based on in vivo P₇₀₀ measurements. Structurally, this deficiency is associated with reduced levels of Psa A/B relative to D1, the absence of specific photosystem I light-harvesting polypeptides [R.M. Morgan et al. (1998) Photosynth Res 56:303–314] and a cytochrome b₆/f complex that exhibits a form of cytochrome f that is approximately 7 kDa smaller than that observed in C. reinhardtii. We conclude that the Antarctic psychrophile, C. subcaudata, is an example of a natural variant deficient in State I–State II transitions.