Structure and function of the elongation sink in thesteruls of higher plants I. Effects of anoxia and IAA on the growth rate and the spatially separate electrogenic ion pumps

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Two spatially separate membrane potentials of the parenchyma symplast (7, 8) and the rate of elongation growth were measured simultaneously in bean hypocotyl segments. Both the membrane potentials, V_<ps> (electric potential difference between parenchyma symplast and organ surface) and V_<px> (electric potential difference between parenchyma symplast and xylem), were rapidly depolarized by anoxia, and were repolarized with re-aeration. Anoxia reduced the growth rate by about 85%, and re-aeration restored it. Changes in the membrane potentials preceded those in the growth rate by 30-50 sec. About 8 min after the application of aerosol generated from 10^<-3> M indole acetic acid (IAA) solution to the segments, V_<ps> began to hyperpolarize, and the growth rate increased with a delay of several minutes after the potential change and subsequently became ten times the control rate. This hyperpolarization of V_<ps> Was due to the increase in the activity of the respiration-dependent electrogenic ion pump at the outer surface membrane of the parenchyma symplast. A clear correlation was observed between the growth rate and pump activity (ΔV_<ps>) with the change in IAA concentration.
日本植物生理学会の論文