Efficiency of Potassium Utilization by Barley Varieties: The Role of Subcellular Compartmentation

Memon, A. R., Saccomani, M. and Glass, A. D. M. 1985. Efficiency of potassium utilization by barley varieties: The role of subcellular compartmentation.¯J. exp. Bot. 36: 1860–1876. The subcellular distributions of K+ in roots of three barley (Hordeum vulgare L.) varieties, grown at 10 and 100 mmol m−3 external K+ ([K+]o) were estimated by compartmental analyses. In general, increased [K+]o caused a 2–3 fold increase in vacuolar [K+], but cytoplasmic [K+] increased only slightly. Nevertheless, the three varieties, which had been selected for study on the basis of their different rates of K+ utilization, showed distinct differences in the allocation of K+ between cytoplasm and vacuole. At 10 mmol m−3 [K+]ovar. Betzes exhibited typical K+ deficiency symptoms while var. Fergus and var. Compana did not, even though Betzes had higher [K+] in shoots and roots. The inefficient utilization of K+ in this variety appears to be associated with a failure to mobilize vacuolar K+ into the cytoplasmic compartment (the ratio of vacuolar: cytoplasmic K+ contents for Betzes was 4.1 compared to 2.7 and 2.5, respectively, for Fergus and Compana). Fergus and Betzes, which demonstrate pronounced growth responses to increased [K+]0 between 10 and 100 mmol m−3, showed significant increases of cytoplasmic [K+] in this range of [K+]o. By contrast, cytoplasmic [K+] in Compana, a variety whose growth is not stimulated by increased [K+]0 (from 10 to 100 mmol m−3) showed virtually no increase. It is suggested that the efficiency of K+ utilization and the growth response to [K+]0 in these varieties are functions of the subcellular distribution of this ion between cytoplasm and vacuole.