Cytokinin stimulates dihydropyridine-sensitive calcium uptake in moss protoplasts

Karen S. Schumaker, Michael J. Gizinski

Research output: Contribution to journalArticle

50 Scopus citations

Abstract

Ca2+ influx through dihydropyridine (DHP)-sensitive Ca2+ channels is thought to be an early event in cytokinin-induced bud formation in moss protonema because DHP antagonists inhibit bud formation in the presence of cytokinin and DHP agonists stimulate bud formation in the absence of cytokinin [Conrad, P. A. & Hepler, P. K. (1988) Plant Physiol. 86, 684-687]. In the present study, we established the presence of a DHP-sensitive Ca2+ transport system by measuring 45Ca2+ influx into moss protoplasts. Ca2+ influx was stimulated by external KCI (up to 5 mM), indicating that transport is voltage-dependent. K+-induced Ca2+ influx was DHP-sensitive with >50% inhibition at 500 nM nifedipine. Ca2+ influx was stimulated by increasing concentrations of the DHP Ca2+ channel agonist Bay K8644 with half-maximal effects at 25 nM; this stimulation was seen only in the absence of K+, suggesting that the agonist works preferentially on polarized membranes. Ca2+ influx was also inhibited by phenylalkylamines (verapamil) and benzothiazepines (diltiazem). The phytohormone 6-benzylaminopurine consistently stimulated Ca2+ influx with a Km value of 1 nM, whereas adenine, indoleacetic acid, and gibberellic acid had no effect on Ca2+ transport. The cytokinins kinetin and trans-zeatin caused a greater stimulation of Ca2+ influx and induced more bud formation than did 6-benzylaminopurine. These results indicate that Ca2+ is taken up into moss protoplasts through voltage-dependent DHP-sensitive Ca2+ channels on the plasma membrane and that one of the cytokinin effects in the induction of bud formation is regulation of this plasma membrane Ca2+ channel.

Original languageEnglish (US)
Pages (from-to)10937-10941
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume90
Issue number23
DOIs
StatePublished - Dec 1 1993

Keywords

  • Bud formation
  • Physcomitrella patens
  • Phytohormone
  • Plant ion channel
  • Signal transduction

ASJC Scopus subject areas

  • General

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