High-affinity potassium transport in barley roots. Ammonium-sensitive and -insensitive pathways.
In an attempt to understand the process mediating K(+) transport into roots, we examined the contribution of the NH(4)(+)-sensitive and NH(4)(+)-insensitive components of Rb(+) transport to the uptake of Rb(+) in barley (Hordeum vulgare L.) plants grown in different ionic environments. We found that at low external Rb(+) concentrations, an NH(4)(+)-sensitive component dominates Rb(+) uptake in plants grown in the absence of NH(4)(+), while Rb(+) uptake preferentially occurs through an NH(4)(+)-insensitive pathway in plants grown at high external NH(4)(+) concentrations. A comparison of the Rb(+)-uptake properties observed in roots with those found in heterologous studies with yeast cells indicated that the recently cloned HvHAK1 K(+) transporter may provide a major route for the NH(4)(+)-sensitive component. HvHAK1 failed to complement the growth of a yeast strain defective in NH(4)(+) transport, suggesting that it could not act as an NH(4)(+) transporter. Heterologous studies also showed that the HKT1 K(+)/Na(+)-cotransporter may act as a pathway for high-affinity Rb(+) transport sensitive to NH(4)(+). However, we found no evidence of an enhancement of Rb(+) uptake into roots due to Na(+) addition. The possible identity of the systems contributing to the NH(4)(+)-insensitive component in barley plants is discussed.
Santa-María
G E
GE
Instituto de Investigaciones Biotecnológicas, Universidad Nacional de San Martín, Instituto Nacional de Tecnologia Industrial, Edificio 24, San Martín 1650, Provincia de Buenos Aires, Argentina. gsantama@iib.unsam.edu.ar
Danna
C H
CH
Czibener
C
C
D001467:Hordeum / Q000254:growth & development / Q000378:metabolism*; D017136:Ion Transport; D018517:Plant Roots / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*
D000644:Quaternary Ammonium Compounds; D011188:Potassium