Calcium influx at the tip of growing root-hair cells of Arabidopsis thaliana

Abstract

The role of extracellular Ca(2+) in root-hair tip growth has been investigated in Arabidopsis thaliana (L.) Heynh. Root-hair length was found to be dependent on the concentration of Ca(2+) in the growth medium, with maximum length achieved at [Ca(2+)] of 0.3-3.0 mM. Using a non-intrusive calcium-specific vibrating microelectrode, an extracellular Ca(2+) gradient was detected at the tips of individual growing root-hair cells. The direction of the gradient indicated a net influx of Ca(2+) into root-hair cells. No gradient was detected near the sides of the root hairs or at the tips of non-growing root hairs. When root hairs were exposed to the Ca(2+)-channel blocker nifedipine, tip growth stopped and the extracellular Ca(2+) gradient was abolished. These results indicate that Ca(2+) influx through plasma-membrane Ca(2+) channels is required for normal root-hair tip growth.

Infection and Invasion of Roots by Symbiotic, Nitrogen-Fixing Rhizobia during Nodulation of Temperate Legumes

“…Disruption of the gradient by a variety of methods results in pollen tube tip growth that is isodiametric (recently reviewed in references 28 and 75). Blocking of Ca 2ϩ channels pharmacologically causes root hairs to stop growing (141,188). Manipulation of the Ca 2ϩ gradients and observations made during reestablishment of Ca 2ϩ gradients indicate that the direction of tip growth is toward regions of highest calcium ion concentration in both pollen tubes and root hairs (13,14,40).…”

The rhd6 Mutation of Arabidopsis thaliana Alters Root-Hair Initiation through an Auxin- and Ethylene-Associated Process

“…Five-day-old seedlings were placed in molten 3% agarose made with APW (Schiefelbein et al, 1992). After solidification, sections were cut using a double-edged razor blade and were stained with a 1:20 dilution of 0.05% toluidine blue (made in 1 mM Mes, pH 6.0) in APW (pH 6.0).…”

Pressure Regulation of the Electrical Properties of Growing Arabidopsis thaliana L. Root Hairs

“…It is already clear that a variety of ion transport processes occur during the process of cellular expansion: the plasma membrane proton pump and electrophoretic K+ uptake are both active; when either is inhibited, growth is inhibited transiently (Lew, 1991). Furthermore, inward Ca2+ currents at the root hair tip are observed only in growing hairs; indeed, externa1 Ca2+ is required for growth (Schiefelbein et al, 1992). Based on the demonstration of a tip-high gradient of stretch-activated Ca'+-permeable channels implicated in tip growth and maintenance of a tip-high gradient of cytosolic Ca2+ in the oomycete Saprolegniaferax (Garrill et al, 1993), it is tempting to believe that the inward Ca'+ current results from the activity of stretch-activated channels located at the growing tip of the root hair.…”

“…A variety of ion transport processes are known to affect Arabidopsis root hair growth. For example, inhibition of the Proton PumP 01 potassium channels transiently inhibits growth (Lew, 1991), and calcium currents inward at the hair tip are associated with actively growing root hairs (Schiefelbein et al, 1992). I find that the electrical properties of the cells are Water relations are a key determinant of growth and development in plants (Milthorpe and Moorby, 1974;Kramer, 1983).…”