Identification and characterization of stretch-activated ion channels in pollen protoplasts.
Pollen tube growth requires a Ca2+ gradient, with elevated levels of cytosolic Ca2+ at the growing tip. This gradient's magnitude oscillates with growth oscillation but is always maintained. Ca2+ influx into the growing tip is necessary, and its magnitude also oscillates with growth. It has been widely assumed that stretch-activated Ca2+ channels underlie this influx, but such channels have never been reported in either pollen grains or pollen tubes. We have identified and characterized stretch-activated Ca2+ channels from Lilium longiflorum pollen grain and tube tip protoplasts. The channels were localized to a small region of the grain protoplasts associated with the site of tube germination. In addition, we find a stretch-activated K+ channel as well as a spontaneous K+ channel distributed over the entire grain surface, but neither was present at the germination site or at the tip. Neither stretch-activated channel was detected in the grain protoplasts unless the grains were left in germination medium for at least 1 h before protoplast preparation. The stretch-activated channels were inhibited by a spider venom that is known to block stretch-activated channels in animal cells, but the spontaneous channel was unaffected by the venom. The venom also stopped pollen tube germination and elongation and blocked Ca2+ entry into the growing tip, suggesting that channel function is necessary for growth.
Dutta
Rajiv
R
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
Robinson
Kenneth R
KR
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D011058:Pollen / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011312:Pressure; D011523:Protoplasts / Q000502:physiology*; D013111:Spider Venoms / Q000494:pharmacology
D015220:Calcium Channels; D007473:Ion Channels; D015221:Potassium Channels; D013111:Spider Venoms; D002118:Calcium