Callose, synthesis

Kauss, H. and Jeblick, W. 1991. Induced calcium uptake and callose synthesis in suspension-cultured cells of Catharanthus roseus are decreased by the protein phosphatase inhibitor okadaic acid. Physiol. Plant. 

Schliipmann, H., Bacic, A., and Read, S.M., 1994, Uridine diphosphate glucose metabolism and callose synthesis in cultured pollen tubes of Nicotiana alata Link et Otto. Plant Physiol. 105 650-670. 

Figure 3 The effect of Triton X-l 00 on total fi-glucan and callose synthesis...

Indeed, given the small amounts of callose that occur in the crude hemi-cellulose fractions of plant cell walls, the synthetase may well be operative all the time, at a low level. The response to injury may not be to produce a new callose synthetase or to activate nascent form of the enzyme, but to remove some simple block to the full function of enzyme already present. In other words, callose synthesis may occur unless it is actively prevented. 

Kohle, H., Jeblick, W., Poten, F. et al. 1985. Chitosan-elicited callose synthesis in soybean cells as a Ca-dependent process. Plant Physiol. 77(3) 544-551. 

Most of the biochemical studies on polysaccharide synthesis to date have been concerned with the formation of homopolymers even when it is known that the synthesis of the homopolymer chain occurs in vivo as part of a heteropolysaccharide (4-6). Cytochemical investigations have made no such distinctions and the polymers located by these studies have nearly always been sites at which heteropolymers were present and where deposition in the wall occurred. The bulk of the polysaccharides that occur in the wall, with the exception of cellulose and callose, are heteropolymers. Generally the polysaccharides of the hemicelluloses and pectins are composed of poly-... 

Plants synthesize l,3-(3-glucanases that hydrolyze the glycans of fungal cell walls. Synthesis is induced by wounding as a defense reaction (see Box 20-E). These glycanases also function in the removal of callose.146... 

Cell walls are biochemically rather inert with reduced digestibility to many organisms because of their complex cellulose, pectin, and lignin molecules. Callose and lignin are often accumulated at the site of infection or wounding (6,7) and form a penetration barrier. Synthesis of inhibitory proteins (e.g., lectins, protease inhibitors) or enzymes (e.g., chitinase, lysozyme, hydrolases, nucleases) that could degrade microbial cell walls or other microbial constituents would be protective, as well as synthesis of peroxidase and phe-nolase, which could help inactivate phytotoxins produced by many bacteria and fungi. These proteins are either stored in the vacuole... 

The nonbranched p(1 3)-linked glucan callose (Fig. 7B) forms helices and is a transient cell wall component with high flexibility. It is found in growing zones synthesis of callose is also an important response mechanism to applied physical or chemical stresses and pathogens. 

Figure 2 The effect of limited proteolysis on (S-glucan synthesis. (A) Total fi-glucan activity (pmoles UDP-l4C-Glc mg-1 protein) after 30 min incubation with various concentrations of proteinase K.(B) Total callose synthesized in these same reactions...

The reaction was also markedly stimulated by the addition of 2-aceta-mido-2-deoxy-D-glucose but C -labeled 2-acetamido-2-deoxy-D-glucose, unlike C -labeled oligosaccharides, was not incorporated into chitin. The requirement for a monosaccharide activator which does not serve as a glycosyl acceptor has been encountered in the synthesis of callose (see p. 341). In neither case is the mechanism of activation known. 

The deposits may function in plugging or sealing the wound caused by injury due to the pathogen and may restrict the loss of molecules and ions and the movement of toxic substances into the tissues. Little is known about induction of the synthesis of the callose although membrane-bound plant 1,3-3-glucan synthetases have been described (112). Callose formation is induced by various chemical and physical stimuli (113, 114, 115) and there is evidence that membrane disruption (116, 117), such as may result from microbial infection, can initiate callose deposition. Whether the stimulus is provided by a specific binding to plasma membranes of microbial metabolites, such as... 

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