ENERGY-REQUIREMENTS FOR MAINTENANCE OF ION CONCENTRATIONS IN ROOTS

Maintenance of ion gradients across plant membranes is considered to be an important process requiring respiratory energy in plant tissues. In order to test this hypothesis, roots of intact plants of potato (Solanum tuberosum L. cv. Alcmaria and cv. Pimpernel) were incubated in a closed circulation system. Electrical conductivity of the solution surrounding these roots was continuously monitored to determine total ion efflux into demineralized water. Anion efflux rate from the symplast was 35 neq (g dry weight)-1 s-1. In combination with literature data on the specific costs of ion transport, this efflux rate yields the respiration rate associated with re-uptake balancing efflux (i.e. maintenance of cellular ion concentrations). The results suggest that energy costs associated with re-uptake of ions may account for up to 25-50% of the total respiratory costs involved in ion influx.