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A Multi-stages Biosynthetic Pathway in Starch Granules Revealed by the Ultrastructure of Maize Mutant Starches

2001; Elsevier BV; Volume: 34; Issue: 1 Linguagem: Inglês

10.1006/jcrs.2001.0375

1095-9963

Catherine Gérard, P. Colonna, Brigitte Bouchet, D.J. Gallant, Véronique Planchot,

Polysaccharides Composition and Applications

Our previous work indicated that starches containing B-type crystallites show low susceptibility to amylolysis and suggested that B-type crystallites have an effect on starch granule organisation. To elucidate granular ultrastructure, double wxae and aedu maize mutant starches containing A- (30 and 50% respectively) and B-type (70 and 50% respectively) crystallites were treated with porcine pancreatic alpha -amylase. The surface structure of the native and degraded starches was studied by scanning electron microscopy, and the internal ultrastructure by transmission electron microscopy after staining with PATAg reagents. The results confirm the influence of B-type crystallites on granule organisation and indicate that starches containing B-type crystallites show an amylolysis attack pattern with minor exocorrosion and major endocorrosion. The granule organisation of A- and B-type starches proposed is not consistent with an onion ring model1and may account for the different behaviour of these starches to amylolysis. Transmission electron microscopy showed that most native wxae and aedu starch granules are composed of a core with a classical alternating structure and a peripheral ring. The peripheral ring in wxae starch was ordered and resistant to amylolysis, whereas that of aedu was disordered and degradable. It is proposed that these two specific forms of granule organisation are attributable to variations in the enzymatic activities of specific starch synthesising enzymes during the course of starch biosynthesis.