Basis for changes in the auxin-sensitivity of Avena sativa (oat) leaf-sheath pulvini during the gravitropic response.
During the gravitropic response, auxin-sensitivity of the lower flanks of leaf-sheath pulvini of Avena sativa (oat) is at least 1000-fold higher than those of the upper flanks and non-gravistimulated pulvini.  When the pulvini are treated with 1 mM Ca2+, a 10-fold increase in auxin-sensitivity of the pulvini is observed.  Related to this difference in auxin-sensitivity, in vitro activation of the vanadate-sensitive H(-)-ATPase by IAA was observed.  Results show that the activation of the H(+)-ATPase by IAA is probably mediated by soluble protein factors and that the H(+)-ATPase prepared from the lower flanks is activated by IAA with a 1000-fold higher auxin-sensitivity as compared with that from the upper flanks of the graviresponding pulvini.  Ammonium sulfate fractionation experiments show that these soluble protein factors are in the 30 to 60% fraction.  Auxin-binding assays reveal that lower flanks contain more high-affinity soluble auxin-binding sites (kD; on the order of 10(-9) M) and less low-affinity soluble auxin-binding sites (kD; on the order of 10(-6) M) than upper flanks.  It is concluded that differential auxin-sensitivity of graviresponding oat-shoot pulvini is achieved by the modulation of affinities of auxin-binding sites in upper and lower flanks of the pulvini, that Ca2+ is involved in such modulation, and that one of the probable cellular functions of these auxin binding sites is the activation of the proton pump on the plasma membranes.
Kim
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Department of Biology, University of Michigan, Ann Arbor 48109-1048, USA.
Kaufman
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PB
D018554:Avena / Q000378:metabolism* / Q000502:physiology; D001665:Binding Sites; D002118:Calcium / Q000502:physiology*; D018522:Gravitropism / Q000502:physiology*; D007210:Indoleacetic Acids / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000502:physiology; D017494:Proton Pumps; D006180:Proton-Translocating ATPases / Q000378:metabolism; D018516:Pulvinus / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D014415:Tunicamycin / Q000494:pharmacology
D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D017494:Proton Pumps; D014415:Tunicamycin; C030737:indoleacetic acid; D006180:Proton-Translocating ATPases; D002118:Calcium