Callose synthetase

Because callose can be assembled so rapidly, it is likely that the primer for callose synthetase is always present in the plant cell, in considerable quantities and at least some of it may well be at, or in transit to, the cell wall at any time. 

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. 

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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