作者机构：
[Qiu, Baosheng; Ai, Yufeng; Gao, Xiang] Huazhong Normal Univ, Coll Life Sci, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Peoples R China.
通讯机构：
[Gao, Xiang] H;Huazhong Normal Univ, Coll Life Sci, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Peoples R China.
关键词：
Nostoc flagelliforme is a terrestrial macroscopic cyanobacterium with a hair-like appearance that is distributed in arid and semi-arid areas. It exhibits remarkable tolerance to extremely acute or long-term dehydration stress. However;it cannot withstand prolonged hydration or water saturation. It appears that too little water limits its growth while too much water becomes a burden. This seemingly contradictory situation is particularly pronounced in N. flagelliforme;reflecting its distinctiveness among Nosotcspecies with respect to the ways they adapt to dry environments. In this review;we call attention to potentially important drought-adaptation mechanisms in this species;including mechanisms related to its morphology;structure;ecophysiology and genetic background;summarizing the available studies relevant to this topic. This species may become a good model for investigating the diverse genetic mechanisms of Nostoc adaptation to dry environments.
摘要：
Nostoc flagelliforme is a terrestrial macroscopic cyanobacterium with a hair-like appearance that is distributed in arid and semi-arid areas. It exhibits remarkable tolerance to extremely acute or long-term dehydration stress. However, it cannot withstand prolonged hydration or water saturation. It appears that too little water limits its growth while too much water becomes a burden. This seemingly contradictory situation is particularly pronounced in N. flagelliforme, reflecting its distinctiveness among Nosotc species with respect to the ways they adapt to dry environments. In this review, we call attention to potentially important drought-adaptation mechanisms in this species, including mechanisms related to its morphology, structure, ecophysiology and genetic background, summarizing the available studies relevant to this topic. This species may become a good model for investigating the diverse genetic mechanisms of Nostoc adaptation to dry environments.
摘要：
Nostoc flagelliforme is a terrestrial, highly drought-tolerant cyanobacterium. However, the molecular mechanism of its drought adaptation still remains little known. In this paper, we attempted to isolate those osmotic stress-regulated cDNA fragments by traditional differential display reverse transcriptase–polymerase chain reaction (DDRT-PCR). The PCR primers were chosen and evaluated from the reported HIP1D sequence-based primers and Ea/Es primers. The physiologically recovered samples were treated with 0.7 M sorbitol for 3 h. A total of 21 cDNA fragments were obtained by DDRT-PCR, and among them, 16 are up-regulated by osmotic stress. BlastX analyses showed that these up-regulated cDNA fragments are most related to ATPases, methyltransferases, transporters, glutathione synthase, signal transduction-associated components, and other unknown proteins. They are potentially important genes for N. flagelliforme to cope with drought stress since they are distinctly up-regulated by osmotic stress. In addition, five cDNA fragments are down-regulated by osmotic stress, such as the cDNA fragment of PSII protein. They may represent those genes involved in normal physiological processes and thus were inhibited by the osmotic stress. Taken together, the interpretation of the functional clues of these osmotic stress-responsive cDNA fragments has provided us an insight into the molecular mechanism of N. flagelliforme coping with the early phase of drought stress.
摘要：
The photosynthetic responses of Microcystis aeruginosa, Scenedesmus obliquus, and Cyclotella meneghiniana to temperature and light regimes were investigated. M. aeruginosa had a higher specific growth rate at 30°C than at 14 and 20°C. Its specific growth rate was the maximum among the three species at 30°C. This suggests that M. aeruginosa could predominate in a water body having high temperature. When exposed to high light, M. aeruginosa showed lower maximal photosystem II (PSII) quantum yield (ΦM), operational PSII quantum yield (
$$ \Phi_{\text{M}}^{\prime } $$
), and active reaction centers per excited cross section (RC/CSm) than S. obliquus and C. meneghiniana. Moreover, after 2 h low light recovery at 14°C and 20°C, the recovery of ΦM,
$$ \Phi_{\text{M}}^{\prime } $$
and RC/CSm in M. aeruginosa were less than the other two species. This indicates that the capacity of high light adaptation of M. aeruginosa is the lowest among the studied species at 14–20°C. When exposed to high light, C. meneghiniana had higher ΦM and
$$ \Phi_{\text{M}}^{\prime } $$
lost and induced higher nonphotochemical quenching at 14–20°C. This suggests that C. meneghiniana developed a higher resistance to high light under low growth temperatures. M. aeruginosa showed the lowest light compensation point among these three species, which indicates that it could utilize low light more efficiently than the other two species. Cyclic electron flow around PSII may play a role in the photoprotective mechanism of all these three species.
摘要：
The phenomenon of cyanobacteria bloom occurs widely in lakes, reservoirs, ponds and slow flowing rivers. Those blooms can have important repercussions, at once on recreational and commercial activities but also on the health of animals and human beings. Indeed, many species are known to produce toxins which are released in water mainly at cellular death. The cyanotoxin most frequently encountered is the microcystin (MC), a hepatotoxin which counts more than 70 variants. The use of fast tests for the detection of this toxin is thus a necessity for the protection of the ecosystems and the human health. A promising method for their detection is a bioassay based on the chlorophyll a fluorescence of algae. Many studies have shown that algae are sensible to diverse pollutants, but were almost never used for cyanotoxins. Therefore, our goals were to evaluate the effect of microcystin on the fluorescence of different species of algae and how it can affect the flow of energy through photosystem II. To reach these objectives, we exposed four green algae (Scenedesmus obliquus CPCC5, Chlamydomonas reinhardtii CC125, Pseudokirchneriella subcapitata CPCC37 and Chlorella vulgaris CPCC111) to microcystin standards (variants MC-LF, LR, RR, YR) and to microcystin extracted from Microcystis aeruginosa (CPCC299), which is known to produce mainly MC-LR. Chlorophyll a fluorescence was measured by PEA (Plant Efficiency Analyzer) and LuminoTox. The results of our experiment showed that microcystins affect the photosynthetic efficiency and the flow of energy through photosystem II from 0.01 μg/mL, within only 15 min. From exposure to standard of microcystin, we showed that MC-LF was the most potent variant, followed by MC-YR, LR and RR. Moreover, green algae used in this study demonstrated different sensitivity to MCs, S. obliquus being the more sensitive. We finally demonstrated that LuminoTox was more sensitive to MCs than parameters measured with PEA, although the latter brings indication on the mode of action of MCs at the photosynthetic apparatus level. This is the first report showing a photosynthetic response within 15 min of exposure. Our results suggest that bioassay based on chlorophyll fluorescence can be used as a rapid and sensitive tool to detect microcystin.
摘要：
Cyanobacteria are known to survive in iron-deficient environments, but the ways in which they acquire Fe and acclimate are not completely understood. Here we report a novel gene sll1263 that is required for Synechocystis sp. strain PCC 6803 to grow under iron-deficient conditions. sll1263 encodes a putative cation diffusion facilitator protein (CDF) that shows 50% amino acid similarity with ferrous iron efflux protein (FieF) of heterotrophic bacteria. In bacteria, the gene product is involved in metal export from the cell, but in Synechocystis sll1263 plays a role in iron uptake. The results show that expression of sll1263 was induced by iron-deficient conditions and its inactivation significantly decreased the growth rate of an sll1263– mutant. Other genes known to be required for Fe acquisition were also strongly up-regulated in the mutant even in the presence of high Fe. Overexpression of sll1263 increased growth under iron deficiency but reduced growth under high-iron stress, suggesting that the gene product was involved in iron uptake rather than detoxification. Expression of FieF in the sll1263– mutant was unable to rescue the Fe-deficient phenotype, but Sll1263 completely restored it. Measurements of cellular iron content and the iron uptake rate showed that they were significantly less in the sll1263– mutant than in the wild type, consistent with a role for sll1263 in iron uptake. We hypothesize that the low-iron habitats and high-iron requirements of cyanobacteria may be the reason why cyanobacterial CDF protein functions in Fe uptake and not efflux as in non-photosynthetic bacteria.
摘要：
Two coastal Synechococcus stains PCC 7002 and CC9311 and one oceanic strain WH8102 were cultured with 41000 nM Fe in Aquil medium. Compared with those under iron-replete conditions, their growth rates were significantly decreased by 59% for WH8102 at 15 nM Fe, by 37% for CC9311 at 15 nM Fe and by 57% for PCC 7002 at 4 nM Fe. Among these three strains, PCC 7002 was the most tolerant to iron limitation while WH8102 was the most sensitive to iron limitation. For each strain under the same iron concentration, the growth rates calculated from the minimal fluorescence yield and cell concentration showed no significant difference. The linear correlation was established between the minimal fluorescence yield and cell concentration although the minimal fluorescence yield per cell varied depending on the strains and iron levels. Under iron-replete conditions, the minimal fluorescence yield per cell was 100-fold higher for the phycoerythrin-lacking strain PCC 7002 than two phycoerythrin-containing strains WH8102 and CC9311. Under iron-deplete conditions, it was increased respectively by 128% and 7% for WH8102 and CC9311 but was decreased by 30% for PCC 7002. Furthermore, the minimal fluorescence yield per cell for PCC 7002 and CC9311 showed little difference throughout the light and dark diel cycle. However, it was significantly higher for WH8102 in the daytime than in the dark.
作者机构：
[Qiu, Bao-Sheng] Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Hubei, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Hubei, Peoples R China.
通讯机构：
[Qiu, Bao-Sheng] C;Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Hubei, Peoples R China.
摘要：
Effects of ammonium on the photosynthetic recovery of Nostoc flagelliforme Berk. et M. A. Curtis were assayed when being rehydrated in low-K(+) or high-K(+) medium. Its photosynthetic recovery was K(+) limited after 3 years of dry storage. The potassium absorption of N. flagelliforme reached the maximum after 3 h rehydration in low-K(+) medium but at 5 min in high-K(+) medium. The K(+) content of N. flagelliforme rehydrated in high-K(+) medium was much higher than that in low-K(+) medium. The maximal PSII quantum yield (F(v)/F(m)) value of N. flagelliforme decreased significantly when samples were rehydrated in low-K(+) medium treated with 5 mM NH(4)Cl. However, the treatment of 20 mM NH(4)Cl had little effect on its F(v)/F(m) value in high-K(+) medium. The relative F(v)/F(m) 24 h EC(50) (concentration at which 50% inhibition occurred) value of NH(4)(+) in high-K(+) medium (64.35 mM) was much higher than that in low-K(+) medium (22.17 mM). This finding indicated that high K(+) could alleviate the inhibitory action of NH(4)(+) upon the photosynthetic recovery of N. flagelliforme during rehydration. In the presence of 10 mM tetraethylammonium chloride (TEACl), the relative F(v)/F(m) 24 h EC(50) value of NH(4)(+) was increased to 46.34 and 70.78 mM, respectively, in low-K(+) and high-K(+) media. This observation suggested that NH(4)(+) entered into N. flagelliforme cells via the K(+) channel. Furthermore, NH(4+) could decrease K(+) absorption in high-K(+) medium.
摘要：
The photosynthetic performance of Microcystis aeruginosa FACHB 854 during the process of UV-B exposure and its subsequent recovery under photosynthetic active radiation (PAR) was investigated in the present study. Eight hours UV-B radiation (3.15Wm−2) stimulated the increase of photosynthetic pigments content at the early stage of UV-B exposure followed by a significant decline. It suggested that UV-B damage was not an immediate process, and there existed a dynamic balance between damage and adaptation in the exposed cells. Short-term UV-B exposure severely inhibited the photosynthetic capability, but it could restore quickly after being transferred to PAR. Further investigations revealed that the PS II of M. aeruginosa FACHB 854 was more sensitive to UV-B exposure than PS I, and the oxygen-evolving complex of PS II was an important damage target of UV-B. The inhibition of photosynthetic performance caused by UV-B could be recovered to 90.9% of pretreated samples after 20h exposure at low PAR, but it could not be recovered in the dark as well as under low PAR in the presence of Chloromycetin. It can be concluded that PAR and de novo protein synthesis were essential for the recovery of UV-B-damaged photosynthetic apparatus. KeywordsBloom-forming cyanobacteria–Electron transport– Microcystis aeruginosa –Photosynthesis–Pigments–UV-B
作者机构：
[Qiu, Bao-Sheng] Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Peoples R China.;Cent China Normal Univ, Hubei Key Lab Genet Regulat & Integrat Biol, Wuhan 430079, Peoples R China.
通讯机构：
[Qiu, Bao-Sheng] C;Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Peoples R China.
关键词：
detoxification;heavy metal;hyperaccumulation
摘要：
Phytochelatin (PC) synthesis is considered necessary for Cd tolerance in non-resistant plants, but roles for PCs in hyper-accumulating species are currently unknown. In the present study, the relationship between PC synthesis and Cd accumulation was investigated in the Cd hyperaccumulator Sedum alfredii Hance. PCs were most abundant in leaves followed by stems, but hardly detected by the reversed-phase high-performance liquid chromatography (HPLC) in roots. Both PC synthesis and Cd accumulation were time-dependent and a linear correlation between the two was established with about 1:15 PCs : Cd stoichiometry in leaves. PCs were found in the elution fractions, which were responsible for Cd peaks in the anion exchange chromatograph assay. About 5% of the total Cd was detected in these elution fractions as PCs were found. Most Cd was observed in the cell wall and intercellular space of leaf vascular cells. These results suggest that PCs do not detoxify Cd in roots of S. alfredii. However, like in non-resistant plants, PCs might act as the major intracellular Cd detoxification mechanism in shoots of S. alfredii.
