Calcium at the Cell Wall‐Cytoplast Interface

Abstract

Attention is given to the role of Ca 2+ at the interface between the cell wall and the cytoplast, especially as seen in pollen tubes. While the cytoplasm directs the synthesis and deposition of the wall, it is less well appreciated that the wall exerts considerable self control and influences activities of the cytoplasm. Ca 2+ participates as a crucial factor in this two way communication. In the cytoplasm, a [Ca 2+ ] above 0.1 μM, regulates myriad processes, including secretion of cell wall components. In the cell wall Ca 2+ , at 10 μM to 10 mM, binds negative charges on pectins and imparts structural rigidity to the wall. The plasma membrane occupies a pivotal position between these two compartments, where selective channels regulate influx of Ca 2+ , and specific carriers pump the ion back into the wall. In addition we draw attention to different factors, which either respond to the wall or are present in the wall, and usually generate elevated [Ca 2+ ] in the cytoplasm. These factors include: (i) stretch activated channels; (ii) calmodulin; (iii) annexins; (iv) wall associated kinases; (v) oligogalacturonides; and (vi) extracellular adenosine 5 -triphosphate. Together they provide evidence for a rich and multifaceted system of communication between the cytoplast and cell wall, with Ca 2+ as a carrier of information.Hepler PK, Winship LJ (2010) Calcium at the cell wall-cytoplast interface.

Pollen Tube Growth Regulation by Free Anions Depends on the Interaction between the Anion Channel SLAH3 and Calcium-Dependent Protein Kinases CPK2 and CPK20

“…Studies based on chemical and genetically encoded reporters showed that tip-focused cytosolic calcium ([Ca 2+ ] cyt ) and proton (H + ) gradients direct pollen tube growth (Pierson et al, 1994;Feijó et al, 1999;Michard et al, 2008). These cytosolic ion gradients are in line with the amplitude and direction of extracellular Ca 2+ fluxes and H + fluxes and it is generally accepted that the cytosolic gradients are, to a great extent, a consequence of local plasma membrane ion fluxes (Michard et al, 2009;Hepler and Winship, 2010). Protons enter the pollen tube tip via a yet unknown transport system, but a pronounced H + efflux is maintained behind the subapical region .…”

Homogalacturonan deesterification during pollen–ovule interaction in Larix decidua Mill.: an immunocytochemical study

“…These ions are taken up by germinating pollen grains and growing pollen tubes forming a specific tip-to-base Ca 2+ gradient. Elevated levels of Ca 2+ at the tube tip are involved in vesicle secretion and in determining the orientation of the tube growth (see the review by Ge et al 2007; Hepler and Winship 2010). Similarly, in gymnosperms, Ca 2+ is taken up by growing pollen tubes (Lazzaro et al 2005; Chen et al 2009), and as Wu et al (2008) found, the Ca 2+ influx in Pinus bungeana is even higher than in angiosperm pollen tubes.…”

Cell-Specific Vacuolar Calcium Storage Mediated by CAX1 Regulates Apoplastic Calcium Concentration, Gas Exchange, and Plant Productivity in Arabidopsis

“…Within the apoplast, the majority of Ca 2+ binds to negatively charged carboxylic groups of galacturonic acids (pectin) and oxalates (Sattelmacher, 2001), with the residual Ca 2+ remaining free in the apoplast for signaling functions (Hirschi, 2004). Pectate cross-linking by Ca 2+ within the cell wall affords greater strength, but little is known about the role of Ca 2+ signaling in regulating cell wall extensibility (Hepler and Winship, 2010). Apoplastic Ca 2+ is also taken up by cells where it fulfills roles in intracellular signaling, but as Ca 2+ is relatively immobile in the cell and is not transported in the phloem, it is not normally redistributed following deposition in leaf vacuoles (Clarkson, 1984;Leigh, 1997;White and Broadley, 2003).…”