Overexpression of phytoene synthase gene from Salicornia europaea alters response to reactive oxygen species under salt stress in transgenic Arabidopsis

A phytoene synthase gene SePSY was isolated from euhalophyte Salicornia europaea L. The 1655 bp full-length SePSY has an open reading frame of 1257 bp and encodes a 419-amino acid protein. The overexpression of SePSY enhanced the growth of transgenic Arabidopsis. When the plants were exposed to 100 mM NaCl, the photosynthesis rate and photosystem II activity (Fv/Fm) increased from 92% to 132% and from 9.3% to 16.6% in the transgenic lines than in the wild-type, respectively. The transgenics displayed higher activities of SOD and POD and lower contents of H(2)O(2) and MDA than the WT. In conclusion, the transgenic lines showed higher tolerance to salt stress than WT plants by increased photosynthesis efficiency and antioxidative capacity. This is the first report about improving the salt tolerance by genetic manipulation of carotenoid biosynthesis.     

A Synechococcus sp. PCC 7942 mutant with a higher tolerance towards bentazone

In this article we describe the partial characterization of a Synechococcus sp. PCC 7942 mutant Mu1 with an enhanced resistance towards the herbicide bentazone (3-isopropyl-1H-2,1,3-benzothiadiazine-4(3H)-one 2,2-dioxide). The mutant was derived from a random mutagenesis with N-methyl-N′-nitro-N-nitrosoguanidine (NSG) and exhibited superior growth rates, pigment content and overall photosynthetic activities under regular growth conditions compared to wild type. Whereas Synechococcus PCC 7942 wild type showed significant photoinhibition, especially in the presence of lincomycin, Mu1 was much more robust. A comparative analysis of the content of several photosynthesis-associated proteins revealed that Mu1 had an increased expression of PsbO on mRNA and protein level and that PsbO is tightly bound to Photosystem II, relative to wild type. This result was substantiated by mass spectrometer measurements of photosynthetic water oxidation revealing a higher stability and integrity of the water oxidizing complex in Mu1 cells grown under regular or calcium deficient conditions. Therefore, our results give rise to the possibility that the overexpression of PsbO in mutant Mu1 confers resistance to reactive oxygen species (ROS) formed as a consequence of bentazone binding to the acceptor side of PS II. In addition, we observed a significantly higher tolerance towards bentazone in iron depleted wild type cells, conditions under which the IdiA protein becomes expressed in highly elevated amounts. As we have previously shown, IdiA preferentially protects the acceptor site of PS II against oxidative stress, especially under iron limitation. Thus, it is likely that IdiA due to its topology interferes with bentazone binding or protects PS II against ROS generated in the presence of bentazone. This revised version was published online in June 2006 with corrections to the Cover Date.     

Overexpression of wheat dehydrin DHN-5 enhances tolerance to salt and osmotic stress in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Late Embryogenesis Abundant (LEA) proteins are associated with tolerance to water-related stress. A wheat (Triticum durum) group 2 LEA proteins, known also as dehydrin (DHN-5), has been previously shown to be induced by salt and abscisic acid (ABA). In this report, we analyze the effect of ectopic expression of Dhn-5 cDNA in Arabidopsis thaliana plants and their response to salt and osmotic stress. When compared to wild type plants, the Dhn-5 transgenic plants exhibited stronger growth under high concentrations of NaCl or under water deprivation, and showed a faster recovery from mannitol treatment. Leaf area and seed germination rate decreased much more in wild type than in transgenic plants subjected to salt stress. Moreover, the water potential was more negative in transgenic than in wild type plants. In addition, the transgenic plants have higher proline contents and lower water loss rate under water stress. Also, Na⁺ and K⁺ accumulate to higher contents in the leaves of the transgenic plants. Our data strongly support the hypothesis that Dhn-5, by its protective role, contributes to an improved tolerance to salt and drought stress through osmotic adjustment.     

Insight into the salt tolerance factors of a wild halophytic rice, <Emphasis Type="Italic">Porteresia coarctata</Emphasis>: a physiological and proteomic approach

Salinity poses a serious threat to yield performance of cultivated rice in South Asian countries. To understand the mechanism of salt-tolerance of the wild halophytic rice, Porteresia coarctata in contrast to the salt-sensitive domesticated rice Oryza sativa, we have compared P. coarctata with the domesticated O. sativa rice varieties under salinity stress with respect to several physiological parameters and changes in leaf protein expression. P. coarctata showed a better growth performance and biomass under salinity stress. Relative water content was conserved in Porteresia during stress and sodium ion accumulation in leaves was comparatively lesser. Scanning electron microscopy revealed presence of two types of salt hairs on two leaf surfaces, each showing a different behaviour under stress. High salt stress for prolonged period also revealed accumulation of extruded NaCl crystals on leaf surface. Changes induced in leaf proteins were studied by two-dimensional gel electrophoresis and subsequent quantitative image analysis. Out of more than 700 protein spots reproducibly detected and analyzed, 60% spots showed significant changes under salinity. Many proteins showed steady patterns of up- or downregulation in response to salinity stress. Twenty protein spots were analyzed by MALDI-TOF, leading to identification of 16 proteins involved in osmolyte synthesis, photosystem functioning, RubisCO activation, cell wall synthesis and chaperone functions. We hypothesize that some of these proteins confer a physiological advantage on Porteresia under salinity, and suggest a pattern of salt tolerance strategies operative in salt-marsh grasses. In addition, such proteins may turn out to be potential targets for recombinant cloning and introgression in salt-sensitive plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Transformation of beta-lycopene cyclase genes from Salicornia europaea and Arabidopsis conferred salt tolerance in Arabidopsis and tobacco

Inhibition of lycopene cyclization decreased the salt tolerance of the euhalophyte Salicornia europaea L. We isolated a β-lycopene cyclase gene SeLCY from S. europaea and transformed it into Arabidopsis with stable expression. Transgenic Arabidopsis on post-germination exhibited enhanced tolerance to oxidative and salt stress. After 8 and 21 d recovery from 200 mM NaCl treatment, transgenic lines had a higher survival ratio than wild-type (WT) plants. Three-week-old transgenic plants treated with 200 mM NaCl showed better growth than the WT with higher photosystem activity and less H(2)O(2) accumulation. Determination of endogenous pigments of Arabidopsis treated with 200 mM NaCl for 0, 2 or 4 d demonstrated that the transgenic plants retained higher contents of carotenoids than the WT. Furthermore, to compare the difference between SeLCY and AtLCY from Arabidopsis, we used viral vector mediating ectopic expression of SeLCY and AtLCY in Nicotiana benthamiana. Although LCY genes transformation increased the salt tolerance in tobacco, there is no significant difference between SeLCY- and AtLCY-transformed plants. These findings indicate that SeLCY transgenic Arabidopsis improved salt tolerance by increasing synthesis of carotenoids, which impairs reactive oxygen species and protects the photosynthesis system under salt stress, and as a single gene, SeLCY functionally showed no advantage for salt tolerance improvement compared with AtLCY.     

Improved salt tolerance in tobacco plants by co-transformation of a betaine synthesis gene <Emphasis Type="Italic">BADH</Emphasis> and a vacuolar Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> antiporter gene <Emphasis Type="Italic">SeNHX1</Emphasis>

Three types of transgenic tobacco plants were acquired by separate transformation or co-transformation of a vacuolar Na⁺/H⁺ antiporter gene, SeNHX1, and a betaine synthesis gene, BADH. When exposed to 200 mM NaCl, the dual gene-transformed plants displayed greater accumulation of betaine and Na⁺ than their wild-type counterparts. Photosynthetic rate and photosystem II activity in the transgenic plants were less affected by salt stress than wild-type plants. Transgenic plants exhibited a greater increase in osmotic pressure than wild-type plants when exposed to NaCl. More importantly, the dual gene transformed plants accumulated higher biomass than either of the single transgenic plants under salt stress. Taken together, these findings indicate that simultaneous transformation of BADH and SeNHX1 genes into tobacco plants can enable plants to accumulate betaine and Na⁺, thus conferring them more tolerance to salinity than either of the single gene transformed plants or wild-type tobacco plants. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Differential expression of LEA proteins in two genotypes of mulberry under salinity

The relative water content (RWC), cell membrane integrity, protein pattern and the expression of late embryogenesis abundant proteins (LEA; group 1, 2, 3 and 4) under different levels of salt stress (0, 1.0, 1.5 and 2.0 % NaCl) were investigated in mulberry (Morus alba L.) cultivars (S1 and ATP) with contrasting salt tolerance. RWC and membrane integrity decreased with increase in NaCl concentration more in cv. ATP than in cv. S1. SDS-PAGE protein profile of mulberry leaves after the NaCl treatments showed a significant increase in 35, 41, 45 and 70 kDa proteins and significant decrease in 14.3, 18, 23, 28, 30, 42, 47 and 65 kDa proteins. Exposure of plants to NaCl resulted in higher accumulation of LEA proteins in S1 than ATP. The maximum content of LEA (group 3 and 4) was detected in S1 at 2.0 % NaCl, which correlates with its salt tolerance.     

A bentazone-resistant mutant of cyanobacterium,Synechococcus elongatus PCC7942 adapts different strategies to counteract on bromoxynil- and salt-mediated oxidative stress

A bentazone-resistant mutant of Synechococcus elongatus PCC7942, called Mu2, tolerated elevated NaCl concentrations. As bentazone and bromoxynil exhibit similar mechanism of action, we investigated whether the mutant also toleratedbromoxynil and found it to be true. The line of investigation was then whether the acclimation strategy for the three stressors, bentazone, bromoxynil and NaCl was same or different. The cellular contents of malondialdehyde, hydrogen peroxide and superoxide increased in wild type strain following all the treatments suggesting their toxicities due to oxidative response. Notwithstanding, there were apparently different anti-oxidative measures pertaining to the herbicide and salinity stress. Glutathione contents and activities of superoxide dismutase, catalase-peroxidase, glutathione S-transferase and glutathione reductase decreased under NaCl, whereas bromoxynil affected only glutathione S-transferase reductase. Moreover, in-gel assays revealed that bromoxynil promoted appearance of isozymes of catalase-peroxidase, while NaCl induced such response only for superoxide dismutase. On the other hand, in Mu2, glutathione peroxidase-reductase and glutathione showed upward trend after bromoxynil exposure, whereas NaCl raised peroxidase and superoxide dismutase. Proteome comparison revealed peroxiredoxin Q to be highly expressed in wild type strain under bromoxynil, whereas NaCl favoured flavodoxin over-expression. Their amounts were already high in Mu2. We suggest that Mu2 acclimatized to bromoxynil in a manner similar to bentazone by upgrading peroxiredoxin Q and glutathione peroxidase-reductase. Conversely, for NaCl it devised another mechanism involving peroxidase and superoxide dismutase, and flavodoxin.     

Ethylene and nitric oxide are involved in maintaining ion homeostasis in <Emphasis Type="Italic">Arabidopsis</Emphasis> callus under salt stress

In the present study, the role of ethylene in nitric oxide (NO)-mediated protection by modulating ion homeostasis in Arabidopsis callus under salt stress was investigated. Results showed that the ethylene-insensitive mutant etr1-3 was more sensitive to salt stress than the wild type (WT). Under 100 mM NaCl, etr1-3 callus displayed a greater electrolyte leakage and Na⁺/K⁺ ratio but a lower plasma membrane (PM) H⁺-ATPase activity compared to WT callus. Application of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor) or sodium nitroprusside (SNP, a NO donor) alleviated NaCl-induced injury by maintaining a lower Na⁺/K⁺ ratio and an increased PM H⁺-ATPase activity in WT callus but not in etr1-3 callus. The SNP actions in NaCl stress were attenuated by a specific NO scavenger or an ethylene biosynthesis inhibitor in WT callus. Under 100 mM NaCl, the NO accumulation and ethylene emission appeared at early time, and NO production greatly stimulated ethylene emission in WT callus. In addition, ethylene induced the expression of PM H⁺-ATPase genes under salt stress. The recovery experiment showed that NaCl-induced injury was reversible, as signaled by the similar recovery of Na⁺/K⁺ ratio and PM H⁺-ATPase activity in WT callus. Taken together, the results indicate that ethylene and NO cooperate in stimulating PM H⁺-ATPase activity to modulate ion homeostasis for salt tolerance, and ethylene may be a part of the downstream signal molecular in NO action.     

Salt stress effects on the photosynthetic electron transport chain in two chickpea lines differing in their salt stress tolerance

The main objective of this study was to evaluate the effects of salt stress on the photosynthetic electron transport chain using two chickpea lines (Cicer arietinum L.) differing in their salt stress tolerance at the germination stage (AKN 87 and AKN 290). Two weeks after sowing, seedlings were exposed to salt stress for 2 weeks and irrigated with 200 ml of 200 mM NaCl every 2 days. The polyphasic OJIP fluorescence transient and the 820-nm transmission kinetics (photosystem I) were used to evaluate the effects of salt stress on the functionality of the photosynthetic electron transport chain. It was observed that a signature for salt stress was a combination of a higher J step (V_J), a smaller IP amplitude, and little or no effect on the primary quantum yield of PSII (φ_Po). We observed for AKN 290 a shorter leaf life cycle, which may represent a mechanism to cope with salt stress. For severely salt-stressed leaves, an inhibition of electron flow between the PQ pool and P700 was found. The data also suggest that the properties of electron flow beyond PSI are affected by salt stress.     

Growth,fluorescence, photosynthetic O<Subscript>2</Subscript> production and pigment content of salt adapted cultures of <Emphasis Type="Italic">Arthrospira</Emphasis> (<Emphasis Type="Italic">Spirulina</Emphasis>) <Emphasis Type="Italic">platensis</Emphasis>

The effect of salt concentration (NaCl) on growth, fluorescence, photosynthetic activities and pigment content of the cyanobacterium Arthrospira platensis has been investigated over 15 days. It has been observed that high NaCl concentration induces an increase of the growth, photosynthetic efficiency (α), phycobilin/chlorophyll ratio and a slight decrease of dark respiration and compensation points. Moreover, high NaCl concentration enhances photosystem II (PSII) activity compared to photosystem I (PSI). Results show that the phycobilin-PSII energy transfer compared to the chlorophyll-PSII (F_695,600/F_695,440) increases. However, data obtained about the maximal efficiency of PSII photochemistry are controversial. Indeed, the Fv/Fm ratio decreases in salt adapted cultures, while at the same time the trapping flux per PSII reaction center (TR₀/RC) and the probability of electron transport beyond Q_A (₀) remain unchanged at the level of the donor and the acceptor sites of PSII. This effect can be attributed to the interference of phycobilin fluorescence with Chl a when performing polyphasic transient measurements.     

过表达OsCatC基因水稻的获得及其耐盐性机理分析

过氧化氢酶C(Catalase C,CatC)作为重要的抗氧化酶,在水稻发育和胁迫响应方面起重要作用.为了探究CatC在盐胁迫响应中的功能及其作用机制,该研究构建了OsCatC过表达转基因水稻,并比较了其耐盐性和相关抗逆生理指标的变化.结果表明:(1)成功构建过量表达载体pCUbi1390-OsCatC-Flag,并经...     

Enhancement of salt tolerance in transgenic rice expressing an Escherichia coli catalase gene, katE

Rice (Oryza sativa) is sensitive to salt stresses and cannot survive under low salt conditions, such as 50 mM NaCl. In an attempt to improve salt tolerance of rice, we introduced katE, a catalase gene of Escherichia coli, into japonica rice cultivar, Nipponbare. The resultant transgenic rice plants constitutively expressing katE were able to grow for more than 14 days in the presence of 250 mM NaCl, and were able to form flower and produce seeds in the presence of 100 mM NaCl. Catalase activity in the transgenic rice plants was 1.5- to 2.5-fold higher than non-transgenic rice plants. Our results clearly indicate that simple genetic modification of rice to express E. coli-derived catalase can efficiently increase its tolerance against salt stresses. The transformant presented here is one of the most salt-tolerant rice plants created by molecular breeding so far.     

Effects of NaCl stress on photochemical activity and thylakoid membrane polypeptide composition of a salt-tolerant and a salt-sensitive rice cultivar

NaCl stress (200 mM) inhibited the electron transport activity of photosystem 2 (PS2) more than that of PS1. The degree of electron transport activity inhibition was lower in the salt-tolerant cultivar Pokkali than in the salt-sensitive cultivar Peta. The polypeptide composition of the thylakoid membrane and PS2 particles did not change after NaCl treatment but there was a difference in polypeptide compositions of thylakoid membrane and PS2 particles between the two cultivars. PS2 particles of cv. Pokkali contained more 33-kDa and 43-kDa polypeptides than cv. Peta. Additionally, PS2 particles after NaCl treatment showed deficiency of 23-kDa outside polypeptides of PS2.     

A cytosolic NADP-malic enzyme gene from rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) confers salt tolerance in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

NADP-malic enzyme (NADP-ME, EC 1.1.1.40) functions in many different pathways in plant and may be involved in plant defense such as wound and UV-B radiation. Here, expression of the gene encoding cytosolic NADP-ME (cytoNADP-ME, GenBank Accession No. AY444338) in rice (Oryza sativa L.) seedlings was induced by salt stress (NaCl). NADP-ME activities in leaves and roots of rice also increased in response to NaCl. Transgenic Arabidopsis plants over-expressing rice cytoNADP-ME had a greater salt tolerance at the seedling stage than wild-type plants in MS medium-supplemented with different levels of NaCl. Cytosolic NADPH/NADP⁺ concentration ratio of transgenic plants was higher than those of wild-type plants. These results suggest that rice cytoNADP-ME confers salt tolerance in transgenic Arabidopsis seedlings.