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Amylolytic Activity in Taproots of Diploid and Tetraploid Medicago sativa L.

1991; Oxford University Press; Volume: 68; Issue: 5 Linguagem: Inglês

10.1093/oxfordjournals.aob.a088269

1095-8290

Jeffrey E. Habben, Jeffrey J. Volenec,

Phytase and its Applications

Our objective was to determine whether starch degradation in taproots of alfalfa (Medicago sativa L.) after defoliation was associated with activity and isoform complement of endo- and exo-amylases. Taproots of genetically comparable diploid (2x) and tetraploid (4x) populations and the tetraploid cultivar Hi-Phy were recovered immediately after defoliation and at approx. 4-d intervals thereafter. Taproot tissues were analysed for starch concentrations and activities of endo- and exo-amylases. An electrophoretic blotting technique was used to examine amylase isoforms. Starch degradation was most rapid in taproots of Hi-Phy, slowest in taproots of the 2x population, with the 4x population being intermediate. The 4x population had a greater initial increase in endo-amylase activity compared to the 2x population; however, Hi-Phy averaged eightfold greater endo-amylase activity than either 2x or 4x populations. Although exo-amylase specific activity was at least 500-fold greater than endo-amylase specific activity in all populations, changes in endo-amylase activity were more closely associated with trends in starch degradation. Multiple isoforms of endo- and exo-amylase were observed in taproots of all populations. Taproots of Hi-Phy contained an endo-amylase isoform that was not apparent in the 2x or 4x populations that may contribute to the high activity of this amylase in taproots of this cultivar. These results, although correlative, suggest an important role for endo-amylase in taproot starch hydrolysis after defoliation.