JXB Advance Access originally published online on November 7, 2005
Journal of Experimental Botany 2005 56(422):3149-3158; doi:10.1093/jxb/eri312
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RESEARCH PAPER |
Uptake of sodium in protoplasts of salt-sensitive and salt-tolerant cultivars of rice, Oryza sativa L. determined by the fluorescent dye SBFI
Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, SE 750 07 Uppsala, Sweden
* To whom correspondence should be addressed. Fax: +46 18 673279. E-mail: Sylvia.Lindberg{at}vbsg.slu.se
In this study, the uptake of Na+ into the cytosol of rice (Oryza sativa L. cvs Pokkali and BRRI Dhan29) protoplasts was measured using the acetoxy methyl ester of the fluorescent sodium-binding benzofuran isopthalate, SBFI-AM, and fluorescence microscopy. By means of inhibitor analyses the mechanisms for uptake and sequestration of Na+ in the salt-sensitive indica rice cv. BRRI Dhan29 and in the salt-tolerant indica rice cv. Pokkali were detected. Less Na+ was taken up into the cytosol of Pokkali than into BRRI Dhan29. The results indicate that K+-selective channels do not contribute to the Na+ uptake in Pokkali, whereas they are the major pathways for Na+ uptake in BRRI Dhan29 along with non-selective cation channels. However, non-selective cation channels seem to be the main pathways for Na+ uptake in Pokkali. Protoplasts from Pokkali leaves took up Na+ only transiently in the presence of extracellular Na+ at 5100 mM. Therefore, it is likely that the protoplasts have a mechanism for fast extrusion of Na+ out of the cytoplasm. Experiments with protoplasts pretreated with NH4NO3 and NH4VO3 suggest that the salt-tolerant Pokkali extrudes Na+ mainly into the vacuole. After cultivation of both cultivars in the presence of 10 or 50 mM NaCl for 72 h, the isolated protoplasts from Pokkali took up less Na+ than the control protoplasts. The results suggest that the salt-tolerance in Pokkali depends on reduced uptake through K+-selective channels and a fast extrusion of Na+ into the vacuoles.
Key words: Benzofuran isophthalate, compartmentalization, fluorescence ratio microscopy, influx, rice, salt stress, sodium uptake
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