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A full-length cDNA of a new serine/threonine (Ser/Thr) protein kinase gene, designated as BnSOS2 (GenBank Acc. No.AY310413), was cloned from Brassica napus by rapid amplification of cDNA ends (RACE). The fulllength cDNA of BnSOS2 was 1779 bp and contained a 1539-bp open reading frame encoding a protein of 512 amino acids. Homology analysis shows that BnSOS2 strongly resembles other Ser/Thr protein kinase genes, and that its putative protein belongs to a typical Ser/Thr kinase family. Northern blot analysis reveals that BnSOS2 is salt-inducible. Our results indicate that BnSOS2 is a new member of the plant SOS2 gene family, which may play an important role in salt tolerance of plants.
Salt usually stresses plants in two ways, osmotic stress and ion toxicity. Plant responds to salinity in two distinct phases through time. It is known that silicon (Si) could alleviate salt stress by decreasing the Na⁺ accumulated in the leaf. In order to determine the function of Si in the two-phase growth response (osmotic and ion toxicity) to salinity, we selected the wheat cultivar ‘‘Changwu 134’’ out of 10 wheat cultivars, and confirmed that it responds to salinity in two distinct phases through time. The fresh weight, leaf area, and leaf Na⁺ concentration were measured during 31 days of 120 mM NaCl supplemented with 1 mM Si treatment. The results revealed that the growth of plants under salinity conditions both with and without Si application were in accordance with the two-phase growth model. Si alleviated the salt stress in the both two-phase growth, but the alleviative effects were more pronounced in the osmotic stress phase than ion toxicity phase. These results clearly showed that Si can enhance plant salt tolerance by alleviating the salt-induced osmotic stress.
Salinization of soils or waters is one of the world’s most serious environmental problems in agriculture. It is necessary to determine the environmental factors under which medicinal and aromatic plants give higher yields and better quality. The problem of salinity is characterized by an excess of inorganic salts and is common in the arid and semi-arid lands, where it has been naturally formed under the prevailing climatic conditions and due to higher rates of evapotranspiration and lack of leaching water. Although more frequent in arid lands, salt-affected soils are also present in areas where salinity is caused by poor quality of irrigation water. Saline soil induces physiological and metabolic disturbances in plants, affecting development, growth, yield, and quality of plants. Plants affects adversely as a result of salinity, seed germination, survival percentage, morphological characteristics, development and yield and its components. In general, salt stress decreases the photosynthesis and respiration rate of plants. Total carbohydrate, fatty acid and protein content were adversely affected due to salinity effect, but increased the level of amino acids, particularly proline. The content of some secondary plant products is significantly higher in plants grown under salt stress than in those cultivated in normal conditions. The salinity tolerance depends on the interaction between salinity and other environmental factors.
Salinity in soil affects about 7 % of the land’s surface and about 5 % of cultivated land. Most importantly, about 20 % of irrigated land has suffered from secondary salinisation and 50 % of irrigation schemes are affected by salts. In many hotter, drier countries of the world salinity is a concern in their agriculture and could become a key issue. Consequently, the development of salt resistant crops is seen as an important area of research. Although there has been considerable research into the effects of salts on crop plants, there has not, unfortunately, been a commensurate release of salt tolerant cultivars of crop plants. The reason is likely to be the complex nature of the effect of salts on plants. Given the rapid increase in molecular biological techniques, a key question is whether such techniques can aid the development of salt resistance in plants. Physiological and biochemical research has shown that salt tolerance depends on a range of adaptations embracing many aspects of a plant’s physiology: one of these the compartmentation of ions. Introducing genes for compatible solutes, a key part of ion compartmentation, in salt-sensitive species is, conceptually, a simple way of enhancing tolerance. However, analysis of the few data available suggests the consequences of transformation are not straightforward. This is not unexpected for a multigenic trait where the hierarchy of various aspects of tolerance may differ between and within species. The experimental evaluation of the response of transgenic plants to stress does not always match, in quality, the molecular biology. We have advocated the use of physiological traits in breeding programmes as a process that can be undertaken at the present while more knowledge of the genetic basis of salt tolerance is obtained. The use of molecular biological techniques might aid plant breeders through the development of marker aided selection.
The suadea salsa full-length S-adenosylmethionine synthetase (SsSAMS2) was introduced into tobacco (Nicotiana tabacum L.) by Agrobacterium tumefaciens-mediated transformation. The gene transformation and expression in tobacco were confirmed by PCR, RT-PCR and Northern blotting analysis. Several transgenic lines (ST lines) overexpressing SsSAMS2 gene under the control of cauliflower mosaic virus 35S promoter showed more seeds number and weight, and accumulated higher free total polyamines (PAs) than wild-type plants (WT lines) and transformants with blank vector (BT lines). Salt stress-induced damage was attenuated in these transgenic plants, in the symptom of maintaining higher photosynthetic rate and biomass. These results that the transgenic plants overexpressing suadea salsa SAMS2 are more tolerant to salt stress than wild-type plants suggest that PAs may play an important role in contributing salt tolerance to plants.
Recently, an increasing attention is focused on the role of silicon in the improvement of plant tolerance to biotic and abiotic stresses. Salinity and drought are important constraints limiting plant growth and yield. Therefore, the main objective of this study was to compare the response of two maize cultivars (KB 1902, KB 1903) to the osmotic stress (induced by 50 mmol∙dm-3 NaCl or 6% PEG - polyethylene glycol) and to investigate the possible ability of silicon (1 mmol∙dm-3 H4SiO4) in mitigating the adverse effects of osmotic stress. The experiments were conducted on 7-day old seedlings grown in hydroponic culture. The obtained results showed that both maize cultivars are very susceptible to osmotic stress. All the examined growth parameters were significantly reduced under stress conditions. Si supply an increased dry matter of shoots and roots of maize cv. KB 1903, however, this positive response did not occur under stress conditions. The exceptions were roots of maize growing in nutrient solution containing NaCl and silicon, their dry matter was 38% higher as compared to NaCl alone. In the case of KB 1902 cv. silicon added to the nutrient solution containing PEG caused approximately 33 and 23% increase in fresh and dry matter of roots in comparison to the PEG treatment alone. Changes in water content in both maize cultivars were relatively small and Si did not influence this parameter. Concentrations of photosynthetic pigments and electrolyte leakage were not affected by the examined treatments. Generally, stress conditions caused a decrease in nitrate reductase activity and Si supply under stress conditions caused the stimulation of the enzyme activity in the leaves of KB 1903. In conclusion, both examined maize cultivars are very sensitive to osmotic stress and the addition of Si to the nutrient solution does not mitigate evidently this negative effect.
Plants adopt several strategies to maintain cellular ion homeostasis, including physiological, biochemical, cellular, subcellular, and molecular mechanisms for fighting against salt stress. We investigated the responses of tolerant Tibetan wild barley (XZ16), tolerant (CM72) and sensitive (Gairdner) barley cultivars at physiological, cellular, and molecular levels. The results revealed that salinity induced a significantly greater reduction in total root length, surface area, diameter, and total volume in Gairdner than in CM72 and XZ16. Analysis of gene expression using quantitative RT-PCR showed that transcripts of vacuolar H⁺-ATPase and inorganic pyrophosphatase (HvHVA/68 and HvHVP1) were more abundant in leaves and roots of XZ16 and CM72 than those of Gairdner. Observation of electron microscopy detected the difference in the damage of leaf and root ultrastructure among the three genotypes under salt stress, with XZ16 and Gairdner being least and most affected, respectively. Subcellular study showed that a primary strategy to protect the cytosol against sodium toxicity was compartmentalization of sodium ions into soluble fraction (vacuoles). Gairdner showed drastically stronger sodium-specific fluorescence visualized by CoroNa-Green, a sodium-specific fluorophore, than CM72 and XZ16.
Rice (Oryza sativa L.) is a principle crop as the main economic importance in Vietnam, providing daily food for over 90 million people in this country. However, a large rice growing areas and rice production are being seriously affected by salinity intrusion, the threats of devastation from climate change. The need to develop salinity tolerance rice varieties to cope with adverse climate change is very imperative. In this study, based on the genome sequence databases of 36 Vietnamese rice landraces, we have identified nine Vietnamese rice landraces carrying nine SalT candidate genes with the sequence similarity to O. sativa SalT (the published GenBank: Z25811.1) which have shown salinity tolerance are included: Te Nuong, Khau mac buoc, Chan thom, Khau giang, Tan ngan, Nang thom cho dao, OM5629, Hom rau and Thom Lai landraces). Amongst them, four rice landraces, Nang thom cho dao, OM5629, Hom rau and Thom lai have revealed two fragments of deletion with six and seven nucleotides which were the most identical to the SalT reference gene. Two primer pairs have been successfully designed to identify the SalT candidate genes in Vietnamese rice landraces. This study provides useful information of salinity tolerance of some Vietnamese rice landraces for breeding programs.
Salinity inhibition of plant growth is the result of osmotic and ionic effect and different plant species have developed different mechanisms to cope with those effects. With the discovery of molecular markers and marker assisted selection technology, it is possible to develop markers that identify salt tolerance. The genetic diversity of tomato genotypes were analyzed using SSRs polymorphic markers and Unweighted Pair Group Method with Arithmetic Mean. Leaves of the twenty tomato genotypes (landraces/accessions in Nigeria) were used to isolate their DNA using Bioland Plant Genomic DNA protocols. Primers were designed from 15 different salt responsive candidate genes, using Vector NTI and the sequence of the genes were obtained from ncbi genomic web site. All 15 primers sets generated shows clear distinct polymorphic profiles as evident from the 6% agarose gel profile. Dendrogram generated shows three groups, none of the panel intermixed in a subgroup. The genetic distance information reported in this study might be used by breeders when planning future crosses among tomato genotypes. From the result obtained UC82B recorded the highest vegetative and yield parameters, therefore, adoption of this genotype could be help to increase the tomato production in Sokoto agro-climatic area.
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