| Plant may be affected by many stress in the process of growth and development, especially salt stress and potassium deficiency stress. The adjustion to salt stress and the absorption of potassium in the K~+-deficient soil is a very complex progress. Salt and low potassium stress can cause the inhibition of growth, leaf chlorosis, and even gradually dying.In addition, there are more lateral and negative geotropism roots under low potassium condition. We analyzed the phenotype of plants under the stress, screened for stress-related genes and investigated function and mechanisms of the genes, which are very important not only to uncover the mechanism of stress tolerance but to cultivate the stress resistant crops.In this study, model plant Arabidopsis thaliana was used to screen high-Na+ tolerant and low-K~+ sensitive mutants at the different salt and potassium stress conditions. The main results were as following:1. Screening for high-Na+ tolerant mutants(1)To investigate the threshold of Na+ concentration that wild-type arabidopsis can live with, the root bending experiment was employed. Wild-type arabidopsis were seeded on the 1/2 MS medium containing different [Na+].This study showed that the roots growth were inhibited under the concentration of Na+ at 200 mmol/L.(2)After screening 5000 activation-tagging mutants, we found 137 lines showed salt tolerance symptom, but the phenotype couldn't be inherited in T2.2. Screening high-Na+ tolerant mutants and low-Na+ sensitive mutants on LK mediumSince the low level Na+ can compensate K~+-deficient as seedling at low potassium condition, we designed both-high salt and low salt concentration with low-K~+ medium in order to identified the mutants with different mechanism of sodium and potassium absorption.(1)We analyzed five kinds of agar and finally chose Seakem LE Agarose for the low-K~+ medium. Which the final [K~+] was 43.07μmol/L throughout this study. The growth of wild type arabidopsis's roots could be inhibted in this K~+ concentration. Because of the compensation effect of sodium to potassium, root would continue to grow on low potassium medium with low concentration salt. As the concentration of Na+ rising, the growth of the roots were gradually inhibited the final [Na+] in the low-K~+ medium was 50 mmol /L and 150 mmol /L in this study.(2)After screening 900 activation-tagging mutants respectively at the two conditions, 37 lines showed salt-tolerant phenotype and 92 lines showed low-salt sensitive in T1, but we failed to found the phenotypes in T2.3. Screening for low-K~+ sensitive mutants on LK medium(1)We also designed an experiment to screen low-K~+ sensitive mutants .In this study we chose common agar to solidify low-K~+ medium. The [K~+] in the LK medium was 66.7μmol/L. The roots of wild-type seedling could still grow, but the growth of low-K~+ sensitive seedlings slowed down under LK condition.(2)After screening 495 activation-tagging mutants, we found a line which can stably inherit the low-K~+ sensitive phenotype which is the inhibition of root growth.(3)The next, we analyzed the physiological traits of the low-K~+ sensitive mutant.It showed that the biomasses of mutant were much less than the wild-type seedlings. Chlorophyll content of the mutant in both 1/2 MS and LK medium were less than the wild-type seedlings, but which was not significantly. The [K~+] of mutant was lower than wild-type in 1//2 MS medium, but higher in LK medium, which was not remarkable .Compared with lks1, hak5, akt1 and sas, we found that the phenotype of mutant was different from these mutants. Leaves of these known mutants showed chlorotic phenotype after 12 days but our mutant did not, and apart from sas, the other mutant roots maintained a faster pace of elongation.compared with our mutant.(4) TAIL-PCR were used to obtain the flanking genomic sequences of the mutant, and the result of the BLAST showed that T-DNA insert in a UTR.We proposed that three genes which were closed to the loci correlated to the pheotype of low potassium sensitivity.
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