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Ca²⁺-Permeable Channels in the Plasma Membrane of Arabidopsis Pollen Are Regulated by Actin Microfilaments¹

State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100094, China

Cytosolic free Ca²⁺ and actin microfilaments play crucial roles in regulation of pollen germination and tube growth. The focus of this study is to test the hypothesis that Ca²⁺ channels, as well as channel-mediated Ca²⁺ influxes across the plasma membrane (PM) of pollen and pollen tubes, are regulated by actin microfilaments and that cytoplasmic Ca²⁺ in pollen and pollen tubes is consequently regulated. In vitro Arabidopsis (Arabidopsis thaliana) pollen germination and tube growth were significantly inhibited by Ca²⁺ channel blockers La³⁺ or Gd³⁺ and F-actin depolymerization regents. The inhibitory effect of cytochalasin D (CD) or cytochalasin B (CB) on pollen germination and tube growth was enhanced by increasing external Ca²⁺. Ca²⁺ fluorescence imaging showed that addition of actin depolymerization reagents significantly increased cytoplasmic Ca²⁺ levels in pollen protoplasts and pollen tubes, and that cytoplasmic Ca²⁺ increase induced by CD or CB was abolished by addition of Ca²⁺ channel blockers. By using patch-clamp techniques, we identified the hyperpolarization-activated inward Ca²⁺ currents across the PM of Arabidopsis pollen protoplasts. The activity of Ca²⁺-permeable channels was stimulated by CB or CD, but not by phalloidin. However, preincubation of the pollen protoplasts with phalloidin abolished the effects of CD or CB on the channel activity. The presented results demonstrate that the Ca²⁺-permeable channels exist in Arabidopsis pollen and pollen tube PMs, and that dynamic actin microfilaments regulate Ca²⁺ channel activity and may consequently regulate cytoplasmic Ca²⁺.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.042754.

^* Corresponding author; e-mail wuwh{at}public3.bta.net.cn; fax 8610–6289–3491.

Received March 15, 2004; returned for revision June 28, 2004; accepted June 28, 2004.

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