High-Affinity Potassium Transport in Barley Roots. Ammonium-Sensitive and -Insensitive Pathways

• Published in: Plant physiology (Bethesda) 2000-05, Vol.123 (1), p.297-306
• Main Authors: Santa-María, G E, Danna, C H, Czibener, C
• Format: Article
• Language: English
• Subjects: Absorption. Translocation of ions and substances. Permeability; Agronomy. Soil science and plant productions; Ammonium; Barley; Biological and medical sciences; Cell growth; Cell physiology; Economic plant physiology; Environmental Stress and Adaptation; Fundamental and applied biological sciences. Psychology; Hordeum - growth & development; Hordeum - metabolism; Ion Transport; Kinetics; Nutrition. Photosynthesis. Respiration. Metabolism; Plant cells; Plant growth; Plant physiology and development; Plant roots; Plant Roots - metabolism; Plants; Plasma membrane and permeation; Potassium; Potassium - metabolism; Quaternary ammonium compounds; Quaternary Ammonium Compounds - pharmacology; Roots; Yeasts
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.123.1.297

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 component dominates 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 $\text{K}^{+}/\text{Na}^{+}$-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.