Ca2+ influx into lily pollen grains through a hyperpolarization-activated Ca2+-permeable channel which can be regulated by extracellular CaM.
Confocal laser scanning microscopy (CLSM) and whole-cell patch-clamp were used to investigate the role of Ca2+ influx in maintaining the cytosolic Ca2+ concentration ([Ca2+]c) and the features of the Ca2+ influx pathway in germinating pollen grains of Lilium davidii D. [Ca2+]c decreased when Ca2+ influx was inhibited by EGTA or Ca2+ channel blockers. A hyperpolarization-activated Ca2+-permeable channel, which can be suppressed by trivalent cations, verapamil, nifedipine or diltiazem, was identified on the plasma membrane of pollen protoplasts with whole-cell patch-clamp recording. Calmodulin (CaM) antiserum and W7-agarose, both of which are cell-impermeable CaM antagonists, lead to a [Ca2+]c decrease, while exogenous purified CaM triggers a transient increase of [Ca2+]c and also remarkably activated the hyperpolarization-activated Ca2+ conductance on plasma membrane of pollen protoplasts in a dose-dependent manner. Both the increase of [Ca2+]c and the activation of Ca2+ conductance which were induced by exogenous CaM were inhibited by EGTA or Ca2+ channel blockers. This primary evidence showed the presence of a voltage-dependent Ca2+-permeable channel, whose activity may be regulated by extracellular CaM, in pollen cells.
Shang
Zhong-lin
ZL
Institute of Molecular and Cell Biology, Hebei Normal University, Shijiazhuang 050016, PR China.
Ma
Li-geng
LG
Zhang
Hai-lin
HL
He
Rui-rong
RR
Wang
Xue-chen
XC
Cui
Su-juan
SJ
Sun
Da-ye
DY
D000906:Antibodies; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002147:Calmodulin / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D027762:Lilium / Q000254:growth & development / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011058:Pollen / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology
D000906:Antibodies; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002147:Calmodulin; D002614:Chelating Agents; D004533:Egtazic Acid; D002118:Calcium