Transport Processes of Two Lolium ✕ Festuca Hybrid Derivatives Differing in Potassium Concentration

To facilitate the development of forages with mineral composition optimal for ruminant production, knowledge of the biochemical and physiological processes determining genotypic differences in nutrient uptake is needed. Experiments were conducted to identify the mechanism(s) that regulated the difference in leaf blade K concentration between two selections of Lolium × Festuca hybriderivatives. Selection differences in rates of K uptake werestimated by measuring Rb uptake by excised roots, and the selectivity of cation uptake for K over Na was determined using intact tillers grown in modified Hoagland's solutions containing varying ratios of K:Na. Differences in Rb uptake by excised roots were of sufficient magnitude to explain differences in leaf blade K concentration. Results indicate differences in K and Na uptake between these two selections reflected an alteration in cation uptake selectivity by roots. Perturbing the plasma membrane integrity by Ca depletion treatments eliminated the difference between selections in K uptake but not in Na uptake. Differences in K uptake were associated with differences in the stimulation of the plasma membrane ATPase by K. These results were interpreted in terms of at least two transport processes contributing to the differences in leaf blade cation concentrations, one process on the plasma membrane affecting K accumulation and another affecting Na accumulation, possibly on the tonoplast membrane.