JXB Advance Access published online on August 23, 2005
Journal of Experimental Botany, doi:10.1093/jxb/eri256
1 Department of Biology, College of Charleston, Charleston, SC 29424, USA
* To whom correspondence should be addressed. Pollen tubes are an established model system for examining polarized cell growth. The focus here is on pollen tubes of the conifer Norway spruce (Picea abies, Pinaceae); examining the relationship between cytosolic free Ca2+, tip elongation, and intracellular motility. Conifer pollen tubes show important differences from their angiosperm counterparts; they grow more slowly and their organelles move in an unusual fountain pattern, as opposed to reverse fountain, in the tip. Ratiometric ion imaging of growing pollen tubes, microinjected with fura-2-dextran, reveals a tip-focused [Ca2+]i gradient extending from 450 nM at the extreme apex to 225 nM at the base of the tip clear zone. Injection of 5,5' dibromo-BAPTA does not dissipate the apical gradient, but stops cell elongation and uniquely causes rapid, transient increases of apical free Ca2+. The [Ca2+]i gradient is, however, dissipated by reversible perfusion of extracellular caffeine. When the basal cytosolic free Ca2+ concentration falls below 150 nM, again a large increase in apical [Ca2+]i occurs. An external source of calcium is not required for germination but significantly enhances elongation. However, both germination and elongation are significantly inhibited by the inclusion of calcium channels blockers, including lanthanum, gadolinium, or verapamil. Modulation of intracellular calcium also affects organelle position and motility. Extracellular perfusion of lanthanides reversibly depletes the apical [Ca2+]i gradient, altering organelle positioning in the tip. Later, during recovery from lanthanide perfusion, organelle motility switches direction to a reverse fountain. When taken together these data show a unique interplay in Picea abies pollen tubes between intracellular calcium and the motile processes controlling cellular organization.
Received February 16, 2005
Accepted June 23, 2005
RESEARCH PAPER
Calcium gradients in conifer pollen tubes; dynamic properties differ from those seen in angiosperms
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2 Department of Biology, University of Massachusetts, Amherst, MA 01003, USA; Present address: Departamento de Biologia Molecular de Plantas, Instituto de Biotecnologia, UNAM, Cuernavaca, Morelos 62271, Mexico
3 Department of Biology, University of Massachusetts, Amherst, MA 01003, USA; Present address: 32 Carcoola Crescent, Normanhurst, NSW 2076, Australia
4 Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
Mark D. Lazzaro, E-mail: lazzarom{at}cofc.edu
Abstract
Undergraduate student when the research was conducted.
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