Influence of external factors on callose and cellulose synthesis during incubation in vitro of intact cotton fibres with [(14)C]sucrose.

Seed clusters, with adhering fibres, from individual locules of 36-d-old fruit capsules of Gossypium arboreum L. were fed with [(14)C]sucrose in vitro. The fibres synthesised, under standard conditions, (1→3)-β-D-glucan (callose) and (1→4)-β-D-glucan (cellulose) in the ratio of approx. 2:1. Under a great variety of different conditions this product ratio remained more or less constant, even when total glucan synthesis was strongly inhibited with 2,4-dinitrophenol or phloretin, or when stimulated with abscisic acid. In attempts to favour cellulose synthesis, no conditions were found where the ratio was substantially reduced. On the other hand, the ratio could be appreciably increased by inhibiting cellulose synthesis, e.g. with 2,6-dichlorobenzonitrile or coumarin, by anionic detergents such as sodium dodecyl sulphate, by low temperatures, or by increasing the osmotic strength of the incubation medium up to conditions causing plasmolysis. Specific degradation of callose, during incubation of the seed clusters, by exogenous exo-(1→3)-β-D-glucanase significantly diminished incorporation of radioactivity into cellulose.