DISTRIBUTION OF AMYLASES WITHIN SWEET-POTATO (IPOMOEA-BATATAS L) ROOT-TISSUE

To understand the effect of various processing techniques on starch hydrolysis in the sweet potato, alpha-amylase, beta-amylase, and starch phosphorylase were localized inside the roots by a combination of immunological detection and activity measurements. Antibodies raised against alpha-amylase, beta-amylase, and starch phosphorylase were used for the detection of immobilized proteins from tissue prints. Distribution of alpha-amylase, beta-amylase, and starch phosphorylase was also assessed by measuring the activity in the outer and inner portion of the root following mechanical separation. Alpha-Amylase tissue-print immunoblots show that this enzyme is strongly localized in the laticifers and in the cambium layers, and very little in storage parenchyma tissues. The tissue prints with anti-beta-amylase demonstrate that this enzyme is ubiquitously distributed throughout the root. Starch phosphorylase immunoblots show that it is concentrated in the anomalous cambium and in the vascular cambium. Furthermore, sectional distribution in all three enzyme activities confirmed results obtained by immunoblotting. The tissue printing technique was simpler, quicker, and usually more precise in screening for the presence of amylases within the root than the activity measurement. The different distributions, particularly that of thermostable alpha-amylase in the outer tissues of the root, may be responsible for rapid starch hydrolysis on the surface during lye peeling, or the discoloration of the cambial and laticifers zones during 6-min lye peel treatment of sweet potato roots.