Enhancement of NaCl tolerance in Arabidopsis thaliana by exogenous L-asparagine and D-asparagine |
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Authors: | Fredric R. Lehle Futai Chen Karen R. Wendt |
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Affiliation: | Dept of Plant Sci., Univ. of Arizona, Tucson, AZ 85721, USA. |
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Abstract: | The tolerances of Columbia Arabidopsis thaliana (L.) Heynh. to NaCl, L-asparagine (L-Asn) and D-asparagine (D-Asn) during seedling establishment on sterile agar medium were determined. Germination and the establishment of upright seedlings with expanded green cotyledons were increasingly inhibited by NaCl concentrations from 20 to 180 m M and radicle growth was prevented at 225 m M NaCl. Tolerance of established seedlings to NaCl was similar at these concentrations. Seedling establishment was prevented at 20 m M L-Asn and 60 m M D-Asn, but L-Asn was not toxic to established seedlings. At lower concentrations, exogenous L- and D-Asn enhanced NaCl tolerance during germination and seedling establishment. Inhibition of seedling establishment by NaCl concentrations below 225 m M was reduced by the addition of L- and D-Asn to the medium. Maximal reduction of NaCl inhibition occurred between 2 and 4 m M for both L- and D-Asn. Higher concentrations of NaCl prevented establishment whether exogenous Asn was present or not. Reduction of NaCl inhibition occurred to the same extent whether L-Asn was presented simultaneously with the NaCl or preloaded for up to 24 h. The total seedling content of Na+ increased about 4-fold to 55 μg (mg dry weight)−1 as the medium concentration of NaCl was increased from 9 μ M to 150 m M NaCl. Total K+ content declined about 80% from about 34 μg (mg dry weight)−1 over the same range of NaCl concentrations. The Na+ uptake and K+ efflux by whole seedlings were similar whether or not NaCl tolerance was increased by exogenous Asn. |
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Keywords: | Arabidopsis thaliana asparagine potassium efflux salt tolerance seed germination sodium uptake |
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