title: Identification of hyperpolarization-activated calcium channels in apical pollen tubes of Pyrus pyrifolia.
abstract: The pollen tube has been widely used to study the mechanisms underlying polarized tip growth in plants. A steep tip-to-base gradient of free cytosolic calcium ([Ca(2+)](cyt)) is essential for pollen-tube growth. Local Ca(2+) influx mediated by Ca(2+)-permeable channels plays a key role in maintaining this [Ca(2+)](cyt) gradient. Here, we developed a protocol for successful isolation of spheroplasts from pollen tubes of Pyrus pyrifolia and identified a hyperpolarization-activated cation channel using the patch-clamp technique. We showed that the cation channel conductance displayed a strong selectivity for divalent cations, with a relative permeability sequence of barium (Ba(2+)) approximately Ca(2+) > magnesium (Mg(2+)) > strontium (Sr(2+)) > manganese (Mn(2+)). This channel conductance was selective for Ca(2+) over chlorine (Cl(-)) (relative permeability P(Ca)/P(Cl) = 14 in 10 mm extracellular Ca(2+)). We also showed that the channel was inhibited by the Ca(2+) channel blockers lanthanum (La(3+)) and gadolinium (Gd(3+)). Furthermore, channel activity depended on extracellular pH and pollen viability. We propose that the Ca(2+)-permeable channel is likely to play a role in mediating Ca(2+) influx into the growing pollen tubes to maintain the [Ca(2+)](cyt) gradient.
authors: College of Horticulture, NanJing Agricultural University, NanJing, China.|HuaiYin Institute of Technology, HuaiAn, China.
authors: Hai-Yong
authors: HY
authors: Qu
authors: College of Life Sciences, HeBei Normal University, Shi Jia Zhuang, China.
authors: Zhong-Lin
authors: ZL
authors: Shang
authors: College of Horticulture, NanJing Agricultural University, NanJing, China.
authors: Shao-Ling
authors: SL
authors: Zhang
authors: HuaiYin Institute of Technology, HuaiAn, China.
authors: Lian-Mei
authors: LM
authors: Liu
authors: College of Horticulture, NanJing Agricultural University, NanJing, China.
authors: Ju-You
authors: JY
authors: Wu
mesh_terms: D002118:Calcium / Q000032:analysis; D015220:Calcium Channels / Q000032:analysis*; D002469:Cell Separation; D004594:Electrophysiology; D005682:Gadolinium / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007811:Lanthanum / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010940:Plant Proteins / Q000032:analysis; D011058:Pollen / Q000502:physiology; D053205:Pollen Tube / Q000737:chemistry*; D027824:Rosaceae / Q000737:chemistry*
chemical_list: D015220:Calcium Channels; D010940:Plant Proteins; D007811:Lanthanum; D005682:Gadolinium; D002118:Calcium