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The Pathway Of Low-affinity Na~+Uptake And Na~+,K~+Homeostasis In Arabidopsis Thaliana Under Salt Stress

Posted on:2015-03-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q WangFull Text:PDF
GTID:1220330467957185Subject:Grassland
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Salinity is one of adverse environments that limits production of crop plants worldwide. High [NaCl]ext disturbs intracellular ion homeostasis, leads to cell membrane dysfunction and attenuation of metabolic activity, which cause growth inhibition and lead ultimately to plant death. Low-affinity Na+uptake is toxic to the cytoplasm of most of crop plant, so reducing Na+influx must be the key step for controlling Na+accumulation in plants and improving salt tolerance of crop plants. However, the pathways by which plants take up Na+are still unclear. At the same time, the distribution of toxic Na+and nutrient K+is still the key of salt tolerance of crop plants. Therefore, we not only research the pathway of low-affinity Na+uptake in plants, but also study on the mechanism of Na+, K+homeostasis in plants, which is also important to improve salt resistance of crop plants. Nevertheless, there is little research on this field. The aims of this Ph.D work, therefore, are to discuss the pathway of low-affinity Na+uptake in Arabidopsis thaliana by analyzing22Na+influx, net Na+and K+uptake rate, Na+and K+accumulations, and the expression patterns of relevant genes in both WT and athkt1;1under different treatments. Simultaneously, we investigated the roles of AtHKT1;1and AtSOS1in mediating homeostasis of Na+and K+in plants. The main foundings and conclusions are as follows:1. Under2.5mM K+plus25mM NaCl,10mM Ca2+and5mM Ba2+could inhibit22Na+influx and net Na+uptake rate in WT; Meanwile, AtHKT1;1was induced by short-term of25mM NaCl, and its expression level up-regulated sharply after3h treatment. The results indicated that NSCC and AtHKT1;1might are main pathway of low-affinity Na+uptake in WT under2.5mM K+plus25mM NaCl. 2. Under2.5mM K+plus25mM NaCl,10mM Ca2+,5mM Ba2+,10mM TEA+and5mM NH4+could inhibit22Na+influx and net Na+uptake rate in athkt1;1significantly; Meanwile, AIHAK5was induced by short-term of25mM NaCl, and its expression level up-regulated sharply after3h treatment. The results indicated that NSCC and AtHAK5might are main pathway of low-affinity Na+uptake in athkt1;1under2.5mM K+plus25mM NaCl.3. After low K+(0.01mM) for7d, net Na+uptake rate, root and shoot Na+concentrations were increased greatly in both WT and athkt1;1, while the tissue water had no difference. These results implied that Na+uptake by roots was induced by K+deficiency, because Na+could instead of K+to keep the osmotic equilibrium and cell turgor under low K+condition.4. Under0.01mM K+plus25mM NaCl, the inhibitors had on effect on net Na+, K+uptake rate in WT. However, compared with2.5mM K+plus25mM NaCl, Na+uptake rate was increased from50nmol/g. RFW/min to130nmol/g. RFW/min in WT under0.01mM K+plus25mM NaCl; Meanwile, compared with2.5mM K+plus25mM NaCl, AtHKT1;1down-regulated as well as AtHAK5up-regulated under0.01mM K+plus25mM NaCl. The results indicated that AtHAK5might are main pathway of low-affinity Na+uptake in WT under0.01mM K+plus25mM NaCl.5. Under0.01mM K+plus25mM NaCl, the inhibitors had on effect on net Na+, K+uptake rate in athkt1;1, which was similar to WT. However, compared with2.5mM K+plus25mM NaCl, Na+uptake rate was increased from50nmol/g. RFW/min to100nmol/g. RFW/min in athkt1;1under0.01mM K+plus25mM NaCl; Meanwile, AtHAK5up-regulated significantly under0.01mM K+plus25mM NaCl, and its expression level increased continuously with prolonging of salt stress. The results indicated that AtHAK5might are main pathway of low-affinity Na+uptake in athkt1;1under0.01mM K+plus25mM NaCl.6. Under2.5mM K+plus25mM NaCl, there were the less root Na+concentration and the more shoot Na+concentration in athkt1;1, and there were the more root K+ concentration and the less shoot K+concentration in athktl;1, however, there was no difference on growth conditon between WT and athktl;1. While atsosl possessed the more root Na+concentration and the lower net K+uptake rate, meanwhile, compared with WT, the growth conditon of atsosl was inhibited significantly. These results implied that coordination between AtHKT1;1and AtSOS1in mediating Na+、K+homeostasis in Arabidopsis thaliana under the normal K+with mild salt stress: AtHKT1;1mainly involved in Na+unloading and AtSOS1mainly involved in Na+exclusion, which kept the low Na+level in plants.7. Under2.5mM K+plus100mM NaCl, there were the less root Na+concentration and the more shoot Na+concentration in athktl;1, and there were the lower net K+uptake rate in athkt1;1. While atsosl possessed the more root and shoot Na+concentrations. These results implied that coordination between AtHKT1;1and AtSOS1in mediating Na+、K+homeostasis in Arabidopsis thaliana under the normal K+with severe salt stress:AtHKT1;1mainly involved in Na+unloading and AtSOS1mainly involved in Na+exclusion, which kept the low Na+level in plants.8. Under0.01mM K+plus25mM NaCl, there were no difference between WT and athkt1;1on both growth conditon and ions accumulations. While atsosl possessed the more root Na+concentration and the less shoot Na+concentration, meanwhile, compared with WT, the growth conditon of atsosl was inhibited significantly. These results implied that coordination between AtHKT1;1and AtSOS1in mediating Na+、K+homeostasis in Arabidopsis thaliana under the low K+with mild salt stress:the activity of AtHKT1;1was inhibted by low K+, AtSOS1mainly involved in Na+loading into the xylem, which could insure Na+insteaded of K+to keep the osmotic equilibrium and cell turgor under low K+condition.9. Under0.01mM K+plus100mM NaCl, there were the less root Na+concentration and the more shoot Na+concentration in athkt1;1, and there were the more root K+concentration and the less shoot K+concentration in athkt1;1, at the same time, it growth conditon was inhibited significantly. While atsosl possessed the less root Na+concentration and net K+uptake rate, meanwhile, compared with WT, the growth conditon of atsosl was inhibited significantly. These results implied that coordination between AtHKTl;1and AtSOS1in mediating Na+、K+homeostasis in Arabidopsis thaliana under the low K+with severe salt stress:AtHKT1;1mainly involved in Na+uptake and AtSOS1mainly involved in Na+loading into the xylem, which could insure Na+insteaded of K+to keep the osmotic equilibrium and cell turgor under low K+condition.In summary, our study suggest that the NSCC, AtHKT1;1and AtHAK5mediate low-affinity Na+uptake together in Arabidopsis thaliana under different Na+, K+conditons; In addition, AtHKT1;1and AtSOSl play the key roles in keeping Na+, K+homeostasis in Arabidopsis thaliana under salt stress and K+deficiency conditions.
Keywords/Search Tags:Arabidopsis thaliana, low-affinity Na~+uptake, 22Na+influx, athkt1, 1, atsos1, Na~+, K~+, mild salt stress, severe salt stress
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