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  • Title: Auxin-induced K+ channel expression represents an essential step in coleoptile growth and gravitropism.
    Author: Philippar K, Fuchs I, Luthen H, Hoth S, Bauer CS, Haga K, Thiel G, Ljung K, Sandberg G, Bottger M, Becker D, Hedrich R.
    Journal: Proc Natl Acad Sci U S A; 1999 Oct 12; 96(21):12186-91. PubMed ID: 10518597.
    Abstract:
    Auxin-induced growth of coleoptiles depends on the presence of potassium and is suppressed by K+ channel blockers. To evaluate the role of K+ channels in auxin-mediated growth, we isolated and functionally expressed ZMK1 and ZMK2 (Zea mays K+ channel 1 and 2), two potassium channels from maize coleoptiles. In growth experiments, the time course of auxin-induced expression of ZMK1 coincided with the kinetics of coleoptile elongation. Upon gravistimulation of maize seedlings, ZMK1 expression followed the gravitropic-induced auxin redistribution. K+ channel expression increased even before a bending of the coleoptile was observed. The transcript level of ZMK2, expressed in vascular tissue, was not affected by auxin. In patch-clamp studies on coleoptile protoplasts, auxin increased K+ channel density while leaving channel properties unaffected. Thus, we conclude that coleoptile growth depends on the transcriptional up-regulation of ZMK1, an inwardly rectifying K+ channel expressed in the nonvascular tissue of this organ.
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