Changes in the Molecular Weight Distribution of the Hemicellulosic Polysaccharides from Rice Coleoptiles Growing Under Different Conditions

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Abstract
The changes in the molecular weight distribution of water-soluble and water-insoluble hemicelluloses from the cell walls of rice coleoptiles growing in air and under water were studied. The growth of rice coleoptiles was remarkably enhanced by growing under water. Water-insoluble hemicellulose, mainly constituted by xyloglucan, suffered an important depolymerization during coleoptile growth. On the other hand, β-glucan and arabinoxylan, the two main polysaccharides of the water-soluble hemicelluloses showed different changes during coleoptile growth. β-glucan showed an increase in its degree of polymerization during the coleoptile fast growth phase and it decreased before coleoptile growth ceased. Arabinoxylan did not show important differences in its mass-average molecular weight. Thus, xyloglucan and β-glucan are the two hemicellulosic polysaccharides involved in the cell wall loosening mechanism during coleoptile growth under both culture conditions.