Roshandel, Parto .
Na+ entrance into rice genotypes: By-pass flow or transporters?
Salinity damage in rice and other salt-sensitive species is due to excessive transport of NaCl through the root system to the leaves and consequently low salt transport to the shoot can be a major trait determining salt resistance. Since the rapid uptake of sodium ions is such a crucial part of the response of rice to salinity, physiological experiments were carried out to compare by-pass flow in two genotypes of rice (IR4630 & IR15324) differing in salt tolerance, because it has been suggested that an apoplastic pathway, by-pass flow, is a major contributory pathway for Na+ entrance into rice plants. Experiments on the youngest fully expanded photosynthetic leaf (the third), using PTS as a tracer for apoplastic movement and Philaenus spumarius as a means to sample the xylem sap, did not demonstrate any apparent difference in by-pass flow between the two lines. The similarity of Na+ concentration in the xylem sap of both genotypes paralleled the results of PTS measurements. Despite the similarity of Na+ concentration in the xylem sap of the third leaves, Na+ concentration in the bulk of these leaves of IR15324 plants (the sensitive line) was about twice that of IR4630 (the tolerant one). Measurements of transpiration over 8 days of salinisation showed the similarity of rates in both lines providing evidence that the greater accumulation of NaCl in IR15324 than IR4630 plants was unlikely to be due to a difference in the delivery of salt to the leaves by an apoplastic route. Results of the current work suggest that the difference in salt tolerance might be a consequence of a difference in the selectivity of transporters and channels to Na+: IR15324 conducts more Na+ and less K+ into its roots upon salinisation than IR4630. The data on Na+/K+ selectivity in the third leaves as well as those in the whole plants of both lines plus the values of Na+ influx were evidence for this suggestion. The lower selectivity of K+ transportation of IR15234 in comparison to IR4630 resulted in a higher Na+ influx from the medium into roots and also caused a higher concentration of Na+ in the photosynthetic tissues of leaves of IR15324. Key words: Rice, Na+ influx, by-pass flow, transporters, salt stress.
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1 - Sussex University, Biology, Biology departmnet, JMS building, The school of life Science, Sussex Uni., Falmer, BN1 9QG, Brighton, Esat Sussex, BN1 9QG, UK
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM