Imaging of the Yellow Cameleon 3.6 indicator reveals that elevations in cytosolic Ca2+ follow oscillating increases in growth in root hairs of Arabidopsis.
In tip-growing cells, the tip-high Ca(2+) gradient is thought to regulate the activity of components of the growth machinery, including the cytoskeleton, Ca(2+)-dependent regulatory proteins, and the secretory apparatus. In pollen tubes, both the Ca(2+) gradient and cell elongation show oscillatory behavior, reinforcing the link between the two. We report that in growing root hairs of Arabidopsis (Arabidopsis thaliana), an oscillating tip-focused Ca(2+) gradient can be resolved through imaging of a cytosolically expressed Yellow Cameleon 3.6 fluorescence resonance energy transfer-based Ca(2+) sensor. Both elongation of the root hairs and the associated tip-focused Ca(2+) gradient show a similar dynamic character, oscillating with a frequency of 2 to 4 min(-1). Cross-correlation analysis indicates that the Ca(2+) oscillations lag the growth oscillations by 5.3 +/- 0.3 s. However, growth never completely stops, even during the slow cycle of an oscillation, and the concomitant tip Ca(2+) level is always slightly elevated compared with the resting Ca(2+) concentration along the distal shaft, behind the growing tip. Artificially increasing Ca(2+) using the Ca(2+) ionophore A23187 leads to immediate cessation of elongation and thickening of the apical cell wall. In contrast, dissipating the Ca(2+) gradient using either the Ca(2+) channel blocker La(3+) or the Ca(2+) chelator EGTA is accompanied by an increase in the rate of cell expansion and eventual bursting of the root hair tip. These observations are consistent with a model in which the maximal oscillatory increase in cytosolic Ca(2+) is triggered by cell expansion associated with tip growth and plays a role in the subsequent restriction of growth.
Monshausen
Gabriele B
GB
Department of Botany, University of Wisconsin, Madison, Wisconsin 53706, USA.
Messerli
Mark A
MA
Gilroy
Simon
S
D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D049108:Cell Enlargement / Q000187:drug effects; D003600:Cytosol / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008164:Luminescent Proteins / Q000032:analysis; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011994:Recombinant Proteins / Q000032:analysis
D007476:Ionophores; D008164:Luminescent Proteins; D011994:Recombinant Proteins; D000001:Calcimycin; D002118:Calcium