Glucose Induced H+ Influx and Transient Currents in Excised Roots: particularly those of Zea mays |
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Authors: | KENNEDY, C. D. STEWART, R. A. |
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Abstract: | The application of D-glucose to solutions bathing excised maize,wheat, pea and bean roots causes a rapid depolarization of theelectrical potentials between the cut tops of the roots andthe bathing solutions. Similar effects are observed for theplasma membrane potentials of maize lateral roots. A flow cell apparatus was used to demonstrate qualitative andquantitative relations between glucose induced H+ influx andthe transient decrease in current through the root. The currentchanges appear to be due entirely to H+ fluxes. Current andH+ fluxes are strongly influenced by external pH, the optimumpH for glucose induced current change being about 4.0. A similarpH optimum was found for 3-O-methyl-D-glucopyranoside but 1-O-methyl--D-glucopyranosidedid not significantly affect the trans-root potential at anypH, suggesting a significant role for the anomeric hydroxylgroup of glucose. Compounds which depolarize the trans-root potential also inhibitthe glucose induced depolarization. Surface -SH groups are probablynot involved in the glucose/H+ cotransport. Eadie-Hofstee plots relating the depolarization of trans-rootpotential to the concentrations of D-glucose or 3-O-methyl-D-glucopyranosidehave shown that Km values increase with increasing monosaccharideconcentration and are very similar to reported values of 3-O-methyl-D-glucopyranosideuptake in maize root segments. Km values for a similar rangeof D-glucose concentrations do not vary significantly with pHor with membrane depolarization due to a 10-fold increase ofKCl concentration. However, Vmax is lowered by an increase inexternal pH or a decrease in trans-root potential. It appearsthat both proton and electrical gradients can affect glucoseinduced H+ influx. The auxin herbicide, 2, 4-dichlorophenoxyethanoic acid (0.01mM) stimulates the glucose induced depolarizations in a mannerconsistent with an increase in cytoplasmic pH. This is discussedin relation to the reported action of indole-3-acetic acid andfusicoccin on maize root tissue. |
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