Expression of potassium-transporter coding genes, and kinetics of rubidium uptake, along a longitudinal root axis

A.J. VALLEJO, M.L. PERALTA, G.E. SANTA-MARÍA

PLANT, CELL AND ENVIRONMENT (PRINT)

Año: 2005 p. 850 - 862

0140-7791

The pattern of mRNA accumulation of genes coding for the putative potassium transporters HvHAK1A, HvHAK1B, HvHAK2, HvHAK3 and HvAKT1 along seminal roots was studied in K+ starved barley (Hordeum vulgare) plants. Accumulation of these transcripts was lower in young, relative to older root zones, indicating the existence of a coordinated spatial pattern of gene regulation. A study of rubidium (Rb+) uptake kinetics showed that for all root zones transport can be dissected into a linear and a saturable component. Paralleling the pattern of mRNA accumulation the Vmax of the saturable term was lowest in the youngest root zone. No differences in the Rb+ Km or in the linear term were observed among root zones. K+ channel blockers Ba2+, Al3+, and TEA exerted no effect on Rb+ uptake from diluted Rb+ solutions, while it was inhibited by Cs+, NH4+, methylamine, and K+ in all root zones. These results show that high-affinity Rb+ transport over the entire axis is mediated by transporters displaying HAK1-like properties. The observation of a differential effect of Na+ on Rb+ uptake along roots is compatible with a change in the proportion and/or the activity of those transport entities following a longitudinal gradient.