Cell wall charge

The Gibbs-Donnan effect is a phenomenon that occurs because of differing concentrations of ions across a semipermeable membrane, like a cell wall. Charge balance is maintained by other ions, like proteins. The differing concentrations set up a concentration cell whose voltage is... 

The strength of cell walls differs among bacteria, yeasts, and molds. The strength also varies with the species and the growth conditions, and must Be determined experimentally. Beads of 0.5 mm are typically used for yeast and bacteria. Recommended bead charge is 85 percent for 0.5 mm beads, and 80 percent for 1 mm beads [Schuette et al.. Enzyme Microbial Technology, 5, 143 (1983)]. 

The presence of nanopartides suspended within the starch matrix would ensure continuous release of ions into the nutrient media. Copper ions released by the nanopartides may attach to the negatively charged bacterial cell wall and rupture it, thereby leading to protein denaturation and cell death [31]. The attachment of both ions and nanopartides to the cell wall caused accumulation of envelope protein precursors, which resulted in dissipation of... 

The galacturonic acids of a plant cell wall mainly belong to smooth chains of homopolygalacturonic acid (PGA) and to hairy regions of rhamnogalacturonan I (RGI). In green plants, other uronic acids can be found in hemicelluloses. Provided they are not methylesterified, all these carboxylic acids deprotonate at the more or less acidic pH of wall water. The electrostatic charges of these polyanions are then compensated by cations ultimately derived from the environment. 

Since cupric ions are paramagnetic, it is possible by electron paramagnetic resonance (EPR) to obtain information on the status and the environment of the Cu ions adsorbed on uronic acids [4, 5]. Nitella cell walls with uronate charges compensated to 9 or 100% with copper in equilibrium with mixed copper and zinc chloride solutions had their EPR spectra recorded at two different temperatures, 93 and 293 °K (Fig. 3.a, b). 

Some divalent cations such as Cu and Pb form very stable complexes with pectate, but are unlikely to be present at sufiScient concentration in the apoplast of plants to form a major fraction of the counterions associated with the pectic fraction in vivo. The Al ion may deserve closer examination, as it is certainly able to displace Ca from cell walls and reaches substantial concentrations in plant roots under some conditions [60,61]. aluminium is not usually considered to be freely translocated, however. Basic peptides with their negative charges spaced at a similar interval to galacturonans (0.43 nm or a small multiple thereof) can in principle have a very high afiBnity for pectate [62,63], but the extensins that are associated with the most insoluble pectic fractions [M] do not appear to have this type of structure. The possibility that the non-extractable pectic polymers in most cell walls are very strongly complexed with some cation other than Ca " cannot be ruled out, but there is little evidence to support it at present. 

In soil, the chances that any enzyme will retain its activity are very slim indeed, because inactivation can occur by denaturation, microbial degradation, and sorption (61,62), although it is possible that sorption may protect an enzyme from microbial degradation or chemical hydrolysis and retain its activity. The nature of most enzymes, particularly size and charge characteristics, is such that they would have very low mobility in soils, so that if a secreted enzyme is to have any effect, it must operate close to the point of secretion and its substrate must be able to diffuse to the enzyme. Secretory acid phosphatase was found to be produced in response to P-deficiency stress by epidermal cells of the main tap roots of white lupin and in the cell walls and intercellular spaces of lateral roots (63). Such apoplastic phosphatase is safe from soil but can be effective only when presented with soluble organophosphates, which are often present in the soil. solution (64). However, because the phosphatase activity in the rhizo-sphere originates from a number of sources (65), mostly microbial, and is much higher in the rhizosphere than in bulk soil (66), it seems curious that plants would have a need to secrete phosphatase at all. 

Bacterial cell walls contain different types of negatively charged (proton-active) functional groups, such as carboxyl, hydroxyl and phosphoryl that can adsorb metal cations, and retain them by mineral nucleation. Reversed titration studies on live, inactive Shewanella putrefaciens indicate that the pH-buffering properties of these bacteria arise from the equilibrium ionization of three discrete populations of carboxyl (pKa = 5.16 0.04), phosphoryl (oKa = 7.22 0.15), and amine (/ Ka = 10.04 0.67) groups (Haas et al. 2001). These functional groups control the sorption and binding of toxic metals on bacterial cell surfaces. 

The chemical and structural features of the membrane and cell wall are extensively discussed elsewhere in this volume (see Chapters 2, 6, 7 and 10). They usually contain numerous charged groups, which, as far as they are not internally compensated by counterions, give rise to the formation of an electric double layer at the interphase. The net charge of membrane surface plus cell wall is counterbalanced by a diffuse charge with opposite sign. This so-called diffuse... 

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