Plasma Membrane H+-ATPase Is Involved in Auxin-Mediated Cell Elongation during Wheat Embryo Development

Abstract

Previous investigations suggested that specific auxin spatial distribution due to auxin movements to particular embryonic regions was important for normal embryonic pattern formation. To gain information on the molecular mechanism(s) by which auxin acts to direct pattern formation in specific embryonic regions, the role of a plasma membrane (PM) ATPase was evaluated as downstream target of auxin in the present study. Western-blot analysis revealed that the PM H ϩ -ATPase expression level was significantly increased by auxin in wheat (Triticum aestivum) embryos (two-three times increase). In bilaterally symmetrical embryos, the spatial expression pattern of the PM H ϩ -ATPase correlates with the distribution pattern of the auxin analog, tritiated 5-azidoindole-3-acetic acid. A strong immunosignal was observed in the abaxial epidermis of the scutellum and in the epidermal cells at the distal tip of this organ. Pseudoratiometric analysis using a fluorescent pH indicator showed that the pH in the apoplast of the cells expressing the PM H ϩ -ATPase was in average more acidic than the apoplastic pH of nonexpressing cells. Cellulose staining of living embryos revealed that cells of the scutellum abaxial epidermis expressing the ATPase were longer than the scutellum adaxial epidermal cells, where the protein was not expressed. Our data indicate that auxin activates the proton pump resulting in apoplastic acidification, a process contributing to cell wall loosening and elongation of the scutellum. Therefore, we suggest that the PM H ϩ -ATPase is a component of the auxin-signaling cascade that may direct pattern formation in embryos.

Mathematical model of morphogen electrophoresis through gap junctions

“…Indeed, many of the same players that have been implicated in left-right asymmetry (K ϩ channels, plasma membrane H ϩ flux, cell membrane transporters, and gradients of serotonin/auxin, regulatory roles of pH, fusicoccin, etc.) are now known to be crucial components of auxin signaling (Arend et al, 2002;Coenen et al, 2002;Pasternak et al, 2002;Hager, 2003;Rober-Kleber et al, 2003;Wind et al, 2004). As with serotonin, there is thought to be a soluble auxin receptor (Dharmasiri et al, 2003;Woodward and Bartel, 2005a,b).…”

“…As with serotonin, there is thought to be a soluble auxin receptor (Dharmasiri et al, 2003;Woodward and Bartel, 2005a,b). Most interestingly, auxin has been suggested to move under electrophoretic control Rathore and Goldsworthy, 1985;Rathore et al, 1988;Rathore and Robinson, 1989;Wang et al, 1989;Rathore et al, 1991;Fischer et al, 1997;Fischer-Iglesias et al, 2001;Rober-Kleber et al, 2003). Paponov et al (2005) proposed an auxin-flow canalization hypothesis: auxin flow, starting by diffusion, induces formation of polar transport system.…”

Humic matter elicits proton and calcium fluxes and signaling dependent on Ca2+-dependent protein kinase (CDPK) at early stages of lateral plant root development

“…These processes are described by the 'acidgrowth theory' [11] that suggests a close relationship between H + pump activity and wall acidification and cell expansion. This mechanism has been also associated with the auxin effects on seed embryo growth [12] and early growth responses to gravistimulation of root cells [13].…”

The Spatially Variable Inhibition by Water Deficit of Maize Root Growth Correlates with Altered Profiles of Proton Flux and Cell Wall pH

“…For image processing, the non-cell wall area in the 488-nm image was first manually deleted using the magic wand tool in Photoshop to eliminate fluorescence from underlying cell walls (Rober-Kleber et al, 2003). The image pairs were then transferred to Matlab, in which a custom program divided each pixel value in the 488-nm image of the walls by the equivalent pixel value in the 457-nm image in order to generate pixel ratios.…”

“…For example, according to the acid growth hypothesis of Rayle and Cleland (1992), maintenance of sufficiently acid pH in the cell wall facilitates turgor-driven expansion by directly loosening the polysaccharide matrix or by optimizing the activity of cell wall proteins and enzymes associated with loosening (Cosgrove, 1997;Tanimoto et al, 2000;Wu and Cosgrove, 2000). Recent findings that cell wall acidification is associated with auxin effects on seed embryo growth (Rober-Kleber et al, 2003) and with early growth responses to gravistimulation of root cells (Taylor et al, 1996;Fasano et al, 2001) support the existence of a close relationship between wall acidification and cell expansion. Similarly, the spatial profile of growth rate along the elongation zone of maize roots has been shown to coincide with the spatial profile of rootsurface acidification (Pilet et al, 1983;Peters and Felle, 1999).…”