Protection of Photosystem II Against UV-A and UV-B Radiation in the Cyanobacterium Plectonema boryanum: The Role of Growth Temperature and Growth Irradiance¶ (original) (raw)
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Environmental and Experimental Botany, 2004
The impact of artificial ultraviolet-B (UV-B 280-315 nm) irradiation and monocrotophos (an organophosphorus insecticide), singly and in combination, on survival, growth and photosynthetic activities and energy transfer within the pigments has been studied in a non-heterocystous cyanobacterium Plectonema boryanum. Survival and growth of the cyanobacterium decreased with selected dose of UV-B (30 min and 90 min) and monocrotophos (5 g ml −1). The various doses of UV-B (30, 60, 90 and 120 min exposures) damaged the photosynthetic pigments, phycocyanin, carotenoids and chlorophyll a (Chl a); phycocyanin, however, appeared to be the main target of UV-B. This was further proved by the prominent decrease in phycocyanin absorption peak in intact cells. 14 C-fixation was found to be more sensitive to UV-B and monocrotophos, singly and in combination than photosynthetic oxygen evolution. Photosynthetic electron transport activity decreased in response to UV-B and monocrotophos individually as well as in their combined dose (UV-B + monocrotophos). This inhibition was due to a greater susceptibility of PSII than PSI. UV-B and monocrotophos either alone or in combination induced inhibition of PSII activity and its partial restoration by artificial electron donors (DPC, NH 2 OH and MnCl 2) suggests that these stresses blocked the electron flow at water oxidation side. However, less restoration in combination of these stresses and 90 min UV-B exposure alone indicated that the PSII reaction centre was also affected. Suppression in emission peak (650 nm) of phycocyanin revealed that both the stresses, either singly or in combination, altered the energy transfer efficiency of phycocyanin to PSII. The present findings suggest that the doses of UV-B radiation and monocrotophos singly and in combination, have adversely affected the photosynthetic activity of P. boryanum, leading to the significant decrease in survival and growth. The interactive effect of both the stresses was, however, less than additive.
European Journal of Biochemistry, 1996
The effects of ultraviolet-B radiation (280-320 nm) on photosystem I1 of $JneChoCJJStk sp. PCC 6803 were investigated at the functional and structural levels. Loss of oxygen-evolving and electrontransport activity, measured by various techniques including Clark electrode polarography, fluorescence induction and fluorescence relaxation after a single turnover flash, are discussed in terms of two types of damage caused by ultraviolet-B radiation : (a) depletion of the plastoquinone pool ; (b) perturbation and degradation of the D1 protein, with cleavage in the second transmembrane segment. These findings are in full agreement with those obtained, both in vivo and in vitro for higher plants for which a donor-side mechanism involving the water-splitting Mn cluster has been proposed for the main cleavage of the D1 protein. At the structural level, complete disruption of the photosystem 11 core is documented as a consequence of (or in parallel with) degradation of the D1 protein. From this point of view, ultraviolet-Binduced photoinhibition is unlike the visible-induced type and less susceptible to repair by synthesis and reinsertion of new D1 protein
Photosynthesis Research, 2013
We have previously investigated the response mechanisms of photosystem II complexes from spinach to strong UV and visible irradiations (Wei et al J Photochem Photobiol B 104:118-125, 2011). In this work, we extend our study to the effects of strong light on the unusual cyanobacterium Acaryochloris marina, which is able to use chlorophyll d (Chl d) to harvest solar energy at a longer wavelength (740 nm). We found that ultraviolet (UV) or high level of visible and near-far red light is harmful to A. marina. Treatment with strong white light (1,200 lmolquanta m -2 s -1 ) caused a parallel decrease in PSII oxygen evolution of intact cells and in extracted pigments Chl d, zeaxanthin, and a-carotene analyzed by high-performance liquid chromatography, with severe loss after 6 h. When cells were irradiated with 700 nm of light (100 lmolquanta m -2 s -1 ) there was also bleaching of Chl d and loss of photosynthetic activity. Interestingly, UVB radiation (138 lmol quanta m -2 s -1 ) caused a loss of photosynthetic activity without reduction in Chl d. Excess absorption of light by Chl d (visible or 700 nm) causes a reduction in photosynthesis and loss of pigments in light harvesting and photoprotection, likely by photoinhibition and inactivation of photosystem II, while inhibition of photosynthesis by UVB radiation may occur by release of Mn ion(s) in Mn 4 CaO 5 center in photosystem II.
The role of growth temperature and growth irradiance on the regulation of the stoichiometry and function of the photosynthetic apparatus was examined in the cyanobacterium Plectonema boryanum UTEX 485 by comparing mid-log phase cultures grown at either 29°C/150 micromol m-2 s-1, 29°C/750 micromol m-2 s-1, 15°C/150 micromol m-2 s-1, or 15°C/10 micromol m-2 s-1. Cultures grown at 29°C/750 micromol m-2 s-1 were structurally and functionally similar to those grown at 15°C/150 micromol m-2 s-1, whereas cultures grown at 29°C/150 micromol m-2 s-1 were structurally and functionally similar to those grown at 15°C/10 micromol m-2 s-1. The stoichiometry of specific components of the photosynthetic apparatus, such as the ratio of photosystem (PS) I to PSII, phycobilisome size and the relative abundance of the cytochrome b6/f complex, the plastoquinone pool size, and the NAD(P)H dehydrogenase complex were regulated by both growth temperature and growth irradiance in a similar manner. This indicates that temperature and irradiance may share a common sensing/signaling pathway to regulate the stoichiometry and function of the photosynthetic apparatus in P. boryanum. In contrast, the accumulation of neither the D1 polypeptide of PSII, the large subunit of Rubisco, nor the CF1 a-subunit appeared to be regulated by the same mechanism. Measurements of P700 photooxidation in vivo in the presence and absence of inhibitors of photosynthetic electron transport coupled with immunoblots of the NAD(P)H dehydrogenase complex in cells grown at either 29°C/750 micromol m-2 s-1 or 15°C/150 micromol m-2 s-1 are consistent with an increased flow of respiratory electrons into the photosynthetic intersystem electron transport chain maintaining P700 in a reduced state relative to cells grown at either 29°C/150 micromol m-2 s-1 or 15°C/10 micromol m-2 s-1. These results are discussed in terms of acclimation to excitation pressure imposed by either low growth temperature or high growth irradiance.
Effects of UV and visible light on cyanobacteria at the cellular level
Photochemical & Photobiological Sciences, 2002
The effect of UV and visible light on cyanobacteria was determined at the cellular level by means of epifluorescence and confocal microscopy techniques. These methods allow the examination of light effects in spatial resolution. Series of measurements were performed to determine the effect of different light qualities and quantities on cyanobacteria. To analyze the effect of the light quality, samples of Anabaena and Scytonema sp. were exposed to intense blue, green or red light applied from the epifluorescence path of the microscope. The fluorescence of the phycobiliproteins was recorded by means of epifluorescence (excitation 550 nm, 20 nm half band width (HBW), emission above 635 nm) or by confocal microscopy (560 nm laser line). Upon exposure to blue or green light the cells showed an increase in fluorescence followed by a sudden and complete loss of fluorescence. Blue light was more effective (bleaching of phycobiliproteins within 45 min) than green light (bleaching within 120 min). Red light was not as effective, and bleaching of the cells took at least 24 h. Initially the cells showed an increase in fluorescence followed by fast bleaching of the fluorescence signal. Cells exposed to UV plus PAR were bleached within 60 min, while cells exposed to photosynthetically active radiation (PAR) only were totally bleached after about 120 min. FL-DHP (dihydropyridine) labeling was performed in two cyanobacteria, Anabaena sp. and Nostoc commune, to visualize L-type calcium channels. Both cyanobacterial strains showed a pronounced FL-DHP signal of the heterocysts and akinetes but only a weak signal from the vegetative cells. The results clearly indicate the presence of calcium channels in these cells. UV radiation decreased the amount of chlorophyll and phycocyanin as could be seen from a decline in the autofluorescence of the cells. In contrast, the FL-DHP signal was not affected by UV.
Acta Protozoologica, 1995
The effects of artificial UV-B irradiation on growth, survival, pigmentation, nitrate reductase (NR), glutamine synthetase (GS) and total protein profile have been studied in a number of Infixing cyanobacterial strains isolated from rice (paddy) fields in India. Different organisms show different effects in terms of growth and survival. Complete killing of Anabaena sp. and Nostoc carmium occurs after 120 min of UV-B exposure, whereas the same occurs only after 150 min of exposure in the case of Nostoc commune and Scytonema sp. Growth patterns of the cells treated with UV-B revealed that Nostoc commune and Scytonema sp. are comparatively more tolerant than Anabaena sp. and Nostoc carmium. Pigment content, particularly phycocyanin, was severely decreased following UV-B irradiation in all strains tested so far. In vivo NR activity was found to increase, while in vivo GS activity was decreased following exposure to UV-B for different durations in all test organisms; although complete inhibition of GS activity did not occur even after 120 min of UV-B exposure. SDS PAGE analysis of the total protein profile of the cells treated with UV-B shows a linear decrease in the protein content with increase in UV-B exposure time. Complete elimination of most of the protein bands occurs after 90 and 120 min of UV-B exposure in Nostoc carmium and Anabaena sp. whereas the same occurs only after 150 min of UV-B treatment in Nostoc commune and Scytonema sp.
2013
Damage of DNA and Photosystem-II are among the most significant effects of UV-B irradiation in photosynthetic organisms. Both damaged DNA and Photosystem-II can be repaired, which represent important defense mechanisms against detrimental UV-B effects. Correlation of Photosystem-II damage and repair with the concurrent DNA damage and repair was investigated in the cyanobacterium Synechocystis PCC6803 using its wild type and a photolyase deficient mutant, which is unable to repair UV-B induced DNA damages. A significant amount of damaged DNA accumulated during UV-B exposure in the photolyase mutant concomitant with decreased Photosystem-II activity and D1 protein amount. The transcript level of psbA3, which is a UV-responsive copy of the psbA gene family encoding the D1 subunit of the Photosystem-II reaction center, is also decreased in the photolyase mutant. The wild-type cells, however, did not accumulate damaged DNA during UV-B exposure, suffered smaller losses of Photosystem-II activity and D1 protein, and maintained higher level of psbA3 transcripts than the photolyase mutant. It is concluded that the repair capacity of Photosystem-II depends on the ability of cells to repair UV-B-damaged DNA through maintaining the transcription of genes, which are essential for protein synthesis-dependent repair of the Photosystem-II reaction center.
2000
The increase of UV-B radiation (280 nm - 320 nm) in the solar spectrum due to the depletion of the stratospheric ozone causes enhanced exposure to UV-B, which is dangerous for all living cells, but especially to photosynthetic organisms due to their light dependency. In search of the basis of UV tolerance in terrestrial cyanobacteria, liquid cultures Nostoc commune derived from field material were treated with artificial UV-B and UV-A irradiation. The induction of various pigments which are thought to provide protection against damaging UV-B irradiation were studied. First, UV-B irradiation induced a rapid increase in carotenoids, especially echinenone and myxoxanthophyll, but did not influence chlorophyll a. Second, an enormous increase of an extracellular, water-soluble UV-A/B-absorbing mycosporine occurred, which was associated with extracellular glycan synthesis. Finally, synthesis of scytonemin, a lipid-soluble, extracellular pigment known to function as UV-A sunscreen was obse...
The green alga Chlorella vulgaris and the cyanobacterium Synechocystis salina cells isolated from Antarctic and mesophilic environments, grown in batch cultures under continuous visible light, were used to assess the effect of the UV-B radiation on the photosystem II (PSII). UV-induced changes in its functional activity were estimated by Pulse Amplitude Modulated chlorophyll fluorescence and oxygen evolution (measured with oxygen rate electrode). The data reveal a relatively stronger UV-Binduced inhibition of oxygen evolution in comparison to that of the primary photochemistry of the PSII in both green algae and cyanobacteria. The inhibition of oxygen evolution was a result of the decrease in the number of functionally active PSII centers. The modification of active reaction centers was also recorded through the relatively more effect on fast operating PSII centers than that of the slow operating PSII centers. On the other hand, the PSII activity of cyanobacteria was more vulnerable to UV-B radiation than that of green algae. Likewise, the mesophilic strain of S. salina was more susceptible to UV-B radiation than the Antarctic isolates.
Biochemical and Biophysical Research Communications, 1998
UV-B induced loss of water oxidation capacity of Exposure of ultraviolet-B (280-320 nm, 1.9 mW m 02 PSII, due to loss of mostly D1 and also D2 protein of s 01) radiation of intact Spirulina platensis for 9 h the PSII reaction centres have been well characterized caused specific loss of the 85.5 KDa anchor protein of (12, 13). It has been claimed that the absorption of UVphycobilisomes, the major light-harvesting antenna B by quinones of the photosynthetic electron transport complex of photosystem II. Associated with the loss chain enhances the free radical induced damage of PSII of 85.5 KDa protein, the UV-B irradiation also caused reaction centres protein D1/D2 and causes irreversible photobleaching of phycobilins and alteration in the damage to the photosynthetic apparatus (14,15). chromophore protein interactions, as evidenced from The studies of UV-B effects on cyanobacteria are limthe visible circular dichroic measurements, and it also ited. The cyanobacteria are oxygenic photosynthetic affected the energy transfer process within the phyprokayotes and are exposed to various types of environcobilisomes, as inferred from the low-temperature, 77 mental stresses which, in turn, have facilitated them K, fluorescence spectral analysis. Our results, thus, to be colonized in a range of habitats. Cyanobacterial clearly demonstrate for the first time that the phycobiphycobilisomes (PBS) serves as the primary light harlisomes effectively act as targets for UV-B induced vesting antenna for PSII, and are attached to the thyladamage of photosynthetic apparatus in cyanobacteria.