The physiological significance of HKT1, a Na+ - coupled high affinity K+ transporter in 'Triticum aestivum'

Full text: Several mechanisms for high affinity K+ uptake by higher plants have been proposed:-an ATP-energised K:+ pump, a K+/H+ antiport and a H+coupled carrier. Recently, a Na+--coupled high affinity K+ transporter, HKT1, was isolated from wheat roots. Whilst Na+K+ symports have been described in charophyte algae, the cloning of HKT1 from wheat is the first, evidence that this type d transport mechanism may function in higher plants. Is the activity of HKT1 an important mechanism involved in K+ acquisition by wheat? The aim of this study was to assess the physiological significance of Na+- coupled high affinity K+ uptake in T. aestivum. To determine whether HKT1 plays a significant role in wheat growth, we measured the dry weights and ion content of plants grown in a range of [K+], with and without Na+. To directly assess the activity of Na+- coupled K+ transport, 86Rb+ and 22Na+ flux analyses were performed on the elongation zones and whole roots of intact seedlings, expressing a high affinity K+ uptake system. The results of these growth and tracer flux studies will be discussed in relation to the expression of the gene encoding HKT1 in T. aestivum