Regulation of K+ transport in tomato roots by the TSS1 locus. Implications in salt tolerance.
The tss1 tomato (Lycopersicon esculentum) mutant exhibited reduced growth in low K+ and hypersensitivity to Na+ and Li+. Increased Ca2+ in the culture medium suppressed the Na+ hypersensitivity and the growth defect on low K+ medium of tss1 seedlings. Interestingly, removing NH4+ from the growth medium suppressed all growth defects of tss1, suggesting a defective NH4(+)-insensitive component of K+ transport. We performed electrophysiological studies to understand the contribution of the NH4(+)-sensitive and -insensitive components of K+ transport in wild-type and tss1 roots. Although at 1 mm Ca2+ we found no differences in affinity for K+ uptake between wild type and tss1 in the absence of NH4+, the maximum depolarization value was about one-half in tss1, suggesting that a set of K+ transporters is inactive in the mutant. However, these transporters became active by raising the external Ca2+ concentration. In the presence of NH4+, a reduced affinity for K+ was observed in both types of seedlings, but tss1 at 1 mm Ca2+ exhibited a 2-fold higher Km than wild type did. This defect was again corrected by raising the external concentration of Ca2+. Therefore, membrane potential measurements in root cells indicated that tss1 is affected in both NH4(+)-sensitive and -insensitive components of K+ transport at low Ca2+ concentrations and that this defective transport is rescued by increasing the concentration of Ca2+. Our results suggest that the TSS1 gene product is part of a crucial pathway mediating the beneficial effects of Ca2+ involved in K+ nutrition and salt tolerance.
Rubio
Lourdes
L
Departamento de Biología Vegetal, Universidad de Málaga, 29071 Málaga, Spain.
Rosado
Abel
A
Linares-Rueda
Adolfo
A
Borsani
Omar
O
García-Sánchez
María J
MJ
Valpuesta
Victoriano
V
Fernández
José A
JA
Botella
Miguel A
MA
D000483:Alleles; D002118:Calcium / Q000378:metabolism; D017343:Genes, Plant; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism*; D017136:Ion Transport; D008094:Lithium / Q000494:pharmacology; D018551:Solanum lycopersicum / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D009154:Mutation; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology
D000644:Quaternary Ammonium Compounds; D012965:Sodium Chloride; D008094:Lithium; D012964:Sodium; D005964:Glucosyltransferases; C023180:trehalose-6-phosphate synthase; D011188:Potassium; D002118:Calcium