Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1557, Issue 1-3, Pages 21-33Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0005-2728(02)00391-2
Keywords
chlorophyll; light acclimation; nonphotochemical energy dissipation; photosynthetic electron transport; xanthophyll; Synechocystis PCC6803
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The hli genes, present in cyanobacteria, algae and vascular plants, encode small proteins [high-light-inducible polypeptides (HLIPs)] with a single membrane-spanning alpha-helix related to the first and third helices of eukaryotic chlorophyll a/b-binding proteins. The HLIPs are present in low amounts in low light and they accumulate transiently at high light intensities. We are investigating the function of those polypeptides in a Synechocystis PCC6803 mutant lacking four of the five hli genes. Growth of the quadruple hli mutant was adversely affected by high light intensities. The most striking effect of the quadruple hli mutation was an alteration of cell pigmentation. Pigment changes associated with cell acclimation to increasing light intensity [i.e. decrease in light-harvesting pigments, accumulation of the carotenoid myxoxanthophyll and decrease in photosystem I (PSI)-associated chlorophylls] were strongly exacerbated in the quadruple hli mutant, resulting in yellowish cultures that bleached in high light and died as light intensities exceeded (>500 mumol photon m(-2) s(-1)). However, these pigment changes were not associated with an inhibition of photosynthesis, as probed by in vivo chlorophyll fluorescence, photoacoustic and O-2-evolution measurements. On the contrary, the HLIP deficiency was accompanied by a stimulation of the photochemical activity, especially in high-light-grown cells. Western blot analyses revealed that the PSI reaction center level (PsaA/B) was noticeably reduced in the quadruple,hli mutant relative to the wild type, whereas the abundance of the PSII reaction center protein D I was comparatively little affected. The hli mutations did not enhance photoinhibition and photooxidation when cells were exposed over a short term to a very high light intensity. Together, the results of this study indicate that HLIPs are critical in the adaptation of the cyanobacterium. to variations in light intensity. The data are consistent with the idea that HLIPs are involved, through a direct or indirect means, in nonphotochemical dissipation of absorbed light energy. (C) 2002 Elsevier Science B.V. All rights reserved.
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