Heat stress induces an inhibition of excitation energy transfer from phycobilisomes to photosystem II but not to photosystem I in cyanobacterium Spirulina platensis

Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Photosynthesis Research Center, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Plant Physiology and Biochemistry (Impact Factor: 2.76). 05/2005; 43(4):389-95. DOI: 10.1016/j.plaphy.2005.03.001
Source: PubMed


The effects of high temperature (30-52.5 degrees C) on excitation energy transfer from phycobilisomes (PBS) to photosystem I (PSI) and photosystem II (PSII) in a cyanobacterium Spirulina platensis grown at 30 degrees C were studied by measuring 77 K chlorophyll (Chl) fluorescence emission spectra. Heat stress had a significant effect on 77 K Chl fluorescence emission spectra excited either at 436 or 580 nm. In order to reveal what parts of the photosynthetic apparatus were responsible for the changes in the related Chl fluorescence emission peaks, we fitted the emission spectra by Gaussian components according to the assignments of emission bands to different components of the photosynthetic apparatus. The 643 and 664 nm emissions originate from C-phycocyanin (CPC) and allophycocyanin (APC), respectively. The 685 and 695 nm emissions originate mainly from the core antenna complexes of PSII, CP43 and CP47, respectively. The 725 and 751 nm band is most effectively produced by PSI. There was no significant change in F725 and F751 during heat stress, suggesting that heat stress had no effects on excitation energy transfer from PBS to PSI. On the other hand, heat stress induced an increase in the ratio of Chl fluorescence yield of PBS to PSII, indicating that heat stress inhibits excitation energy transfer from PBS to PSII. However, this inhibition was not associated with an inhibition of excitation energy transfer from CPC to APC since no significant changes in F643 occurred at high temperatures. A dramatic enhancement of F664 occurring at 52.5 degrees C indicates that excitation energy transfer from APC to the PSII core complexes is suppressed at this temperature, possibly due to the structural changes within the PBS core but not to a detachment of PBS from PSII, resulting in an inhibition of excitation energy transfer from APC to PSII core complexes (CP47 + CP43). A decrease in F685 and F695 in heat-stressed cells with excitation at 436 nm seems to suggest that heat stress did not inhibit excitation energy transfer from the Chl a binding proteins CP47 and CP43 to the PSII reaction center and the decreased Chl fluorescence yields from CP43 and CP47 could be explained by the inhibition of the energy transfer from APC to PSII core complexes (CP47 + CP43).

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    • "The paradoxical effects of optimal temperature for growth and photosynthesis should be examined in a further study. In the photosynthetic apparatus, photosystem II (PSII) is believed to be the most heat-sensitive component, and its activity is inhibited significantly by heat stress[28]. This might be the reason that photosynthetic parame-ters at 40 °C decreased sharply and could not be detected during the latter case of experiments. "
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    • "As mentioned above, short heat treatments of Synechocystis PCC 6803 cells led to significant decoupling of PBSs from the reaction centers [16]. Similar observations were made on heat-stressed Anacystis nidulans [47] and Spirulina platensis cells [48]. PBS fluorescence likewise increased significantly when A. nidulans cells were exposed to temperatures below 10 °C [49]. "
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    ABSTRACT: Exposure of cyanobacterial or red algal cells to high light has been proposed to lead to excitonic decoupling of the phycobilisome antennae (PBSs) from the reaction centers. Here we show that excitonic decoupling of PBSs of Synechocystis sp. PCC 6803 is induced by strong light at wavelengths that excite either phycobilin or chlorophyll pigments. We further show that decoupling is generally followed by disassembly of the antenna complexes and/or their detachment from the thylakoid membrane. Based on a previously proposed mechanism, we suggest that local heat transients generated in the PBSs by non-radiative energy dissipation lead to alterations in thermo-labile elements, likely in certain rod and core linker polypeptides. These alterations disrupt the transfer of excitation energy within and from the PBSs and destabilize the antenna complexes and/or promote their dissociation from the reaction centers and from the thylakoid membranes. Possible implications of the aforementioned alterations to adaptation of cyanobacteria to light and other environmental stresses are discussed.
    Full-text · Article · Nov 2011 · Biochimica et Biophysica Acta
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    • "It should be noted that we have previously investigated the effects of heat stress on excitation energy transfer from PBS to PSII and PSI in S. platensis cell. We found that heat stress had no effect on excitation energy transfer from PBS to PSI (Wen et al., 2005). However, the results of the present study demonstrated that salt stress induced an increase in excitation energy transfer to PSI (Fig. 5). "
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    ABSTRACT: The effects of salt stress (0-0.8M NaCl) on excitation energy transfer from phycobilisomes to photosystem I (PSI) and photosystem II (PSII) in the cyanobacterium Spirulina platensis were investigated. Salt stress resulted in a significant decrease in photosynthetic oxygen evolution activity and PSII electron transport activity, but a significant increase in PSI electron transport activity. Analyses of the polyphasic fluorescence transients (OJIP) showed that, with an increase in salt concentration, the fluorescence yield at the phases J, I and P declined considerably and the transient almost leveled off at 0.8M NaCl. Analyses of the JIP test demonstrated that salt stress led to a decrease in the maximal efficiency of PSII photochemistry, the probability of electron transfer beyond Q(A), and the yield of electron transport beyond Q(A). In addition, salt stress resulted in a decrease in the electron transport per PSII reaction center, but an increase in the absorption per PSII reaction center. However, there was no significant change in the trapping per PSII reaction center. Furthermore, there was a decrease in the concentration of the active PSII reaction centers. Analyses of 77K chlorophyll fluorescence emission spectra excited either at 436 or 580nm showed that salt stress inhibited excitation energy transfer from phycobilisomes to PSII but induced an increase in the efficiency of energy transfer from phycobilisomes to PSI. Based on these results, it is suggested that, through a down-regulation of PSII reaction centers and a shift of excitation energy transfer in favor of PSI, the PSII apparatus was protected from excess excitation energy.
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