Maintenance of ion gradients across plant membranes is considered to b
e an important process requiring respiratory energy in plant tissues.
In order to test this hypothesis, roots of intact plants of potato (So
lanum tuberosum L. cv. Alcmaria and cv. Pimpernel) were incubated in a
closed circulation system. Electrical conductivity of the solution su
rrounding these roots was continuously monitored to determine total io
n 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 re
spiration rate associated with re-uptake balancing efflux (i.e. mainte
nance 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.