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Study On Physiological And Molecular Basis Of Salt Cress (Thellungiella Halophila) Salt Tolerance

Posted on:2005-11-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z L WangFull Text:PDF
GTID:1100360152966452Subject:Botany
Abstract/Summary:PDF Full Text Request
High salt stress disrupts homeostasis in water potential and ion distribution. This disorder of homeostasis occurs at both the cellular and the whole plant levels. Drastic changes in ion and water homeostasis lead to molecular damage, growth inhibition and even death. Therefore, one important strategy for plants to survive under salt stress is to re-establish the homeostasis in high salt environment. Both ionic and osmotic homeostasis must be restored. With salt cress(T. halophila), a halophytic model system, we constructed a NaCl-treated cDNA library and sequenced randomly selected clones and constructed a EST Database; compared the growth and osmotic adjustment of salt cress with Arabidopsis; analyzed the expression of ThP5CS under various stresses and in different plant tissues, and discussed the relation between the expression of ThP5CS with Proline synthesis and osmotic adjustment; analyzed the effects of various stresses on the expression of ThTRX h and ThGOLS; constructed ThTRX h-GST fusion protein and expressed in E. Coli., and completed the constructions of binary Ti vector with ThTRX h, ThGOLS and ThSOS3, and transformed into Arabidopsis, respectively; and also completed the construction of gene silencing vector with ThSOS3 and transformed into salt cress. The transgenic Arabidopsis plants overexpressing ThTRX h, ThGOLS and ThSOS3 were also been analyzed to detect salt tolerance of the transgenic plants, respectively. The results were shown as follows: 1. Construction of EST Database from Salt CressWe constructed a NaCl-treated cDNA library of T. halophila and sequenced randomly selected clones. 1699 ESTs were generated. Among them, 1178 ESTs had significantly homology to previously identified genes. By sequence analysis, 813 unique clones were identified:549 shoewd homology to previous identified genes, 264 sequences matched uncharacterized genes. All our EST Data were submitted to dbEST in GenBank and are available on the internet now. The identity between T. halophila and Arabidopsis thaliana cDNA sequences in our EST collection are 95.76% in total ESTs and 95.36% in non-redundant clones. At least eight classes of genes were related to the salt tolerance, which accounted for about 18.89% of total sequenced ESTs.2. Comparation of Growth and Osmotic Adjustment of Salt Cress(T. halophila) and Arabidopsis under NaCl stressFour-week-old seedlings of salt cress and Arabidopsis were treated with different concentrations of NaCl, respectively. Salinity threshold for salt cress growth was determined. The changes in dry and fresh weights, K+ and Na+ contents, free amino acid, Proline, organic acid, soluble sugars were compared between salt cress and Arabidopsis. And the effects of NaCl on osmotic potential and MDA content were also compared between the two plants.The results showed that NaCl 300mmol/L was a salinity threshold for salt cress growth which decreased the survival rate by 50% relative to the medium without salt. Low and moderate salinity(50-150mmol/L NaCl) did not inhibit the growth of salt cress and only the high salinity(up to 250-300mmol/L NaCl) could inhibit its growth, while Arabidopsis growth always decreased with the increase in NaCl concentration.Under NaCl stress, Changes in Na+ and K+ content showed different tendency between salt cress and Arabidopsis.The decrease in K+content of Arabidopsis leaves was more than that of salt cress. The Na+ content in salt cress roots increased slightly with the increase in salinity, while the Na+ content in Arabidopsis roots had more increase with salinity increase. Our data also showed that Arabidopsis could accumulated more Proline and soluble sugars and result in more decrease in osmotic potential than salt cress. The MDA content in salt cress leaves almost had no changes under salt stress, while that of Arabidopsis leaves increased significantly with the increase of NaCl concentration. All these data demonstrated that salt cress had more salt tolerance than Arabidopsis. 3.Cloning and Expression Analysis of ThP5CS Gene under Various StressesPartia...
Keywords/Search Tags:salt cress, EST data, osmotic adjustment, ThP5CS, ThTRX h, ThGOLS and ThSOS3, plant salt tolerance
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