- High-affinity potassium transport in barley roots: Ammonium-sensitive and -insensitive pathways

SANTA MARIA G.E.; DANNA CRISTIAN; CZIBENER CECILIA

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Lugar: Rockville; Año: 2000 vol. 123 p. 297 - 306

0032-0889

In an attempt to understand the process mediating K transport into roots, we examined the contribution of the NH4 sensitive and NH4-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 NH4-sensitive componentdominates Rb uptake in plants grown in the absence of NH4, while Rb uptake preferentially occurs through an NH4-insensitive pathway in plants grown at high external NH4 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 NH4-sensitive component. HvHAK1 failed to complement the growth of a yeast strain defective in NH4 transport, suggesting that it could not act as an NH4 transporter. Heterologous studies also showed that the HKT1 K/Na-cotransporter may act as a pathway for high-affinity Rb transport sensitive to NH4. 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 NH4-insensitive component in barley plants is discussed.