The Roles of Alpha-Amylase in Starch Metabolism in the Cotton Plant

Chong W. Chang


 
ABSTRACT

Cotton leases contained two forms of alpha-mylase, starch-granule-bound and soluble. Both forms had similar optimum pH values for maximum activities. The pH range was 4.5 to 5.0. In responses of these enzymes to various pH levels, the bound enzymes, however, showed a single sharp maximum activity indicating a single enzyme operation. In contrast, the soluble enzyme showed a broad activity peak suggesting, a multiple enzyme participation in this system. Starch content decreased rapidly during the 12-hr dark period. This change was not related to the levels of soluble alpha-amylase activity, but to the change of bound enzyme activity. Starch accumulated gradually during the 10-hr light period. The maximum bound alpha-amylase activity occurred during the period of rapid increase in starch accumulation rate and then this activity decreased as the starch content increased. The chance of soluble enzyme activity, however, was not related to that of starch accumulation. Starch content from leaves of various ages harvested during the light period was closely related to the levels of alpha-anylase activity from these leaves. To characterize starch degradation products influenced by bound alpha-anylase activity, starch granules bound with this enzyme were incubated at 30 C for various time periods. The products were fractionated by use of Bio-gel columns, namely P-2 (exclusion limit, 100-1800 daltons) and P-10 (exclusion limit, 1800-20,000 daltons). From the former column, two major peaks were observed. They were the first excluded peak containing large molecular weight maltodextrins and the second retarded peak containing small molecular weight products such as maltose, maltotriose, maltotetraose, and maltopentaose. The maltodextrins excluded from the P-2 column were further fractionated by the P-10. The various sizes of all maltodextrins were included in this column indicating the range orf molecular weight was 1,800-20,000 daltons. The small molecular weight inaltodextrins could not serve as a primer for Q-enzyme. The large molecular weight maltodextrins, however, acted as active primers for this branching enzyme.



Reprinted from Proceedings of the 1983 Beltwide Cotton Production Research Conference pg. 64
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998