New Ways to Look at the Architecture of Plant Cell Walls

Abstract

We report the use of Ni2" and Co2l on free-hand sections of soybean (Glycine max L.) and Bidens sp to localize polygalacturonates. In soybean only the hourglass cells of the seedcoat stain intensely. In the pod the epidermis of the outer pod wall and a few layers of subepidermal cells stain lightly, while that part of the funiculus adjacent to the seedcoat palisade epidermal cells stains heavily and the neck of the funiculus close to the pod also stains. In Bidens stem sections, the walls of the collenchyma stain most intensely.We are interested in the architecture of the cell walls of dicotyledonous plants. The general plan of a typical wall involves cellulose microfibrils embedded in a more or less amorphous matrix; the microfibrils resist tension, the matrix resists compression. The matrix includes hemicelluloses and pectins. Growing cells produce walls appropriate to their place in the cell body by controlling the relative rates of synthesis and secretion of the various wall components. In the case of pectin, because it is secreted with its uronic acid residues largely in the methyl ester form, dramatic changes in physical properties can be achieved in muro. Secretion ofpectin methyl esterase (PME) or perhaps activation of PME already in place generates uronic acids with pKs in the range of 3.5 to 5. Thus protons are generated in muro. These lower the pH and raise the osmotic potential of the wall. PME preferentially hydrolyzes uronic acid esters in blocks, thereby generating blocks of polygalacturonate residues that can bind Ca2" to form egg box structures with a high linear charge density (2). These structures consist of dimers and larger aggregates (6). The gelling ability of partially deesterified pectins in dilute solutions is remarkably sensitive to degree of esterification and concentration of Ca2" (and Ba2 , Sr", Cu2", Cd2", and Co2" but not K+ or Mg2+; Ni2" was not tried) (8

Exocytosis Precedes and Predicts the Increase in Growth in Oscillating Pollen Tubes

“…While the chemical basis for PI fluorescence in the pollen tube apical wall has not been established, we suspect that its positive charge allows the dye to interact with negative charges on pectin (i.e., carboxyl residues) in a manner similar to several other pectin dyes, such as ruthenium red (Ischebeck et al, 2008;Szumlanski and Nielsen, 2009), coriphosphine O (Weis et al, 1988), and cobalt and nickel (Varner and Taylor, 1989;Jauneau et al, 1997). That PI fluorescence and DIC thickness measurements provide nearly identical results strongly supports the conclusion that these two independent assays respond to the same feature.…”

“…Although the basis for staining is not known, PI carries positive charges and may interact with the negative charges that are present on the pectins, especially the carboxyl residues. The basis for PI staining may therefore be similar to other reagents better known for their ability to react with pectin, such as ruthenium red (Ischebeck et al, 2008;Szumlanski and Nielsen, 2009), coriphosphine O (Weis et al, 1988), and nickel or cobalt (Varner and Taylor, 1989;Jauneau et al, 1997), which also carry positive charges. We have applied PI to growing pollen tubes of lily and tobacco.…”

Last exit: senescence, abscission, and meristem arrest in Arabidopsis.

“…For example, specific cellulase (i.e., endo-p-l,4-glucanase) genes are induced in AZs in association with the abscission process (Varner and Taylor, 1989;de1 Campillo and Lewis, 1992;Lashbrook et al, 1994). In bean, a specific cellulase isoform is ,induced at the separation layer but also in a less localized pattern in adjacent vascular tissue (de1 Campillo et al, 1990;Tucker et al, 1991).…”

Reduction in Pectin Methylesterase Activity Modifies Tissue Integrity and Cation Levels in Ripening Tomato (Lycopersicon esculentum Mill.) Fruits

“…We have utilized the ability of Ni2+ to replace cations in plant tissues (Varner and Taylor, 1989) to visualize the modifications in fruit pectins due to low PME activity. Figure 4 shows binding of Ni2+ to fruit tissues from transgenic 37-81-with low PME activity and wild-type Rutgers plants.…”