Callose deposition

LPS also has effects on cell wall alterations such as callose deposition (Keshavarzi et al., 2004) and on PR gene induction (Zeidler et al., 2004 Silipo et al., 2005). In some cases specific effects of a particular LPS on plant gene induction are observed. LPS from the crucifer pathogen Xcc induced expression of a gene encoding a defense-related (->-(1 -3) glucanase when applied to turnip leaves at 1 p,g per ml. In contrast, LPS from Escherichia coli and Salmonella enterica were ineffective at concentrations up to 50 p,g per ml (Newman et al., 1995). Such specific effects may reflect the ability of particular plants to recognize structural features within LPS that are not widely conserved. 

The nonprotein amino acid, / -aminobutyric acid (BABA) protected Arabidopsis against the oomycete pathogen Peronospora parasitica through activation of natural defence mechanisms of the plant such as callose deposition, the hepersensitive response, and the formation of the trailing necroses [158]. Seed treatment with BABA also shown to protect Pennisetum glaucum (pear millet) systematically from the attack of Sclerospora graminicola [159]. 

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... 

Stanghellini M E, Aragaki M 1966 Relation of periderm formation and callose deposition to an-thracnose resistance in papaya fruit. Phytopathology 56 444-450... 

This method gives a bright fluorescence of callose but also a side effect due to the presence of chlorophyll. Chlorophyll dispersed in the specimen yields a red fluorescence all around the tissue, especially a red layer on the surface of the organs due to chlorophyll deposition in any lipid substances, such as a cuticle. 

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-... 

Deposition of the matrix substances and formation of the microfibrils are accompanied by a sequence of related processes that lead to the development and differentiation of the cell wall this sequence includes expansion of the wall, changes in the composition of the polysaccharides, organization and orientation of the different layers, deposition of callose for formation of pores in phloem, lignification (see p. 299), and other processes. Considerable information has been obtained about the mechanism of some of these processes and the factors that affect them this information has been reviewed by leading molecular biologists, and will very briefly be mentioned here because of its relevance to cell-wall formation and to the constitution of cell-wall polysaccharides of interest to carbohydrate chemists. According to the new concepts, the transformations of the cell wall are effected, or are assisted, by the presence of a variety of enzymes, proteins, and, perhaps, even ribonucleic acid to the extent that primary... 

Deposition of callose, gums, phenolics and polyphenolics in and around infected cells. Increases in hydroxyproline-rich glycoproteins in cell walls (, , , , )... 

Callose Formation. Deposits or papillae between host plasma membranes and cell walls are seen in plant tissues infected by fungi, nematodes and viruses (30). These deposits often react positively with the aniline blue fluorochrome and are believed to be composed of callose, a polysaccharide complex which may include 3-glucans containing 1,3- and 1,4-linkages (HL). 

A recent cytochemical study by Waterkeyn (1981) has shown that callose always forms the innermost layer of the secondary wall of cotton fibre cells, just outside the plasmalemma. Hence the deposition of cellulose must occur outside this layer and cellulose molecules must either pass through it, or be constructed at its outer edge. No evidence was obtained to show whether the callose was or was not converted into cellulose, but Waterkeyn favoured the view that callose represents a permanently restored interface across which cellulose molecules are matured and organised to form the secondary wall. A careful distinction was drawn between the physiological and traumatic depositions of callose and there is, indeed, no evidence that the two processes are very closely related. 

In the development of phloem, the plasma membranes ends of the cells are joined by elaborate plasmodesmata, which make contact through channels in the cell wall. Callose is deposited around these and the sieve tube is the much specialised chain of cells that results, with residual, functional cytoplasm still present, connected across the pores of the sieve plates. Connections to companion cells also remain though the lateral walls and these must serve to sustain the c5hoplasm of the sieve tubes. 

The deposition of callose in the vicinity of plasmodesmata disturbs symplasmic communication (this will be described in detail below) between cells and - in this manner -influences the exchange of signals through plasmodesmata (Fig. 10 A). When callose is deposited in the cell wall it can interrupt the exchange of signals through the apoplast (Fig. 10 B). 

Fig. 10. The deposition of callose in the plasmodesmata regions, suggesting the closure of plasmodesmata only between some of the explants cells (A), and in the cell wall, suggesting the isolation of neighbouring cells via apoplast (B) Arabidopsis explants during SE hand-cut sections stained with aniline blue bar = 15 pm).

Studies with Cichorium and Camellia japonka showed that the deposition of callose is a prerequisite for somatic embryogenesis (Dubois et al., 1990 Pedroso Pais, 1992). The same results were described for Trijblium (Meheswaran Williams, 1985) and coconut (Verdeil et al, 2001). 

Ultrastructural and histological studies on Cichorium during SE have shown that the first sign of SE is the deposition of callose in the cell wall (Verdus et al, 1993). Analysis performed on Eleutherococcus senticosus explants showed that after plasmolysis the amount of callose increased in comparison with xmtreated explants and - moreover - it was shown that callose is deposited between the plasma membrane and the cell wall (You et al., 2006). 

The markers for the early stages of SE during the transition from the somatic to the embryogenic stage of cell development are present within the cell walls. These markers refer to the chemical composition of the extracellular matrix of a cell undergoing the process of transition, which involves changes in AGP and LTP, pectic epitojjes, and callose and hpid substances deposited within the cell wall. 

Callose is a morphologically distinctive polysaccharide that occurs in granular form deposited around sieve plates and on the side of sieve-tube pores. Callose is a 3-1,3-linked D-glucan with no detectable branching (Aspinall, 1980). In higher plants, callose is deposited as a response to wounding or infection by microorganisms (Bacic et al., 1988). 

DeLeeuw G T N 1985 Deposition of lignin, suberin and callose in relation to the restriction of infection by Botrytis cinerea in ghost spots of tomato fruits. Phytopath Z 112 143-152... 

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