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Starch Degradation Metabolism towards Sucrose Synthesis in Germinating Araucaria araucana Seeds ¹

Departamento de Biologia, Facultad de Ciencias Basicas y Farmaceuticas, Universidad de Chile, Santiago, Chile, Department of Biology, Washington University, St. Louis, Missouri 63130

As starch is the main seed reserve material in both species of Araucaria of South America, A. araucana and A. angustifolia, it is important to understand starch breakdown in both embryo and megagametophyte tissues of Araucaria seeds. Sugar analysis by thin layer chromatography indicates that sucrose is the main sugar produced in both tissues. Enzyme reactions coupled to benzidine oxidation indicate that sucrose is the main sugar moved from the megagametophyte to the growing regions of the embryo via the cotyledons.

Phosphorylase was detected in both embryo and megagametophyte tissues by the formation of [³²P]glucose-1-P and by formation of [¹⁴C] amylopectin from [¹⁴C]glucose-1-P. The enzyme activity increases 5-fold in both embryo and gametophyte to a peak 18 hours after the start of imbibition. Debranching enzyme, -glucosidase, and hexokinase are also present in both embryonic and megagametophytic tissues.

Branched glucan oligosaccharides accumulate during this time, reaching a maximum 40 hours after imbibition starts, and decline after germination occurs.

The pattern of activity of the enzymes studied in this work suggests that starch degradation is initiated by -amylase and phosphorylase in the embryo and by phosphorylase mainly in the megagametophyte. Sucrose-P synthase seems to be the enzyme responsible for sucrose synthesis in both tissues.

This article has been cited by other articles:

				J. J. Waghorn, T. del Pozo, E. A. Acevedo, and L. A. Cardemil The role of two isoenzymes of {alpha}-amylase of Araucaria araucana (Araucariaceae) on the digestion of starch granules during germination J. Exp. Bot., March 1, 2003; 54(384): 901 - 911. [Abstract] [Full Text] [PDF]