Amylase Activity in Taproots of Medicago sativa L. and Lotus corniculatus L. Following Defoliation

Although the patterns of starch metabolism in taproots of alfalfa(Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatusL.) have been characterized, little is known regarding the activitiesof starch-degrading enzymes in taproots of these species. Ourobjective was to determine how defoliation influences starchdegradation and activities of amylases in taproots of alfalfaand birdsfoot trefoil. In Exp. 1, amylolytic activities andstarch concentrations in taproots of defoliated and undefoliatedplants were compared on days 0, 3, 7, 10, and 14 after defoliation.Taproot starch concentrations declined in defoliated plants,while increasing in taproots of undefoliated plants. Exoamylaseactivities in taproots of defoliated plants did not change withdefoliation, while endoamylase activities increased 2-fold indefoliated alfalfa and 50% in defoliated birdsfoot trefoil plantswhen compared to undefoliated plants. In Exp. 2, activity andisoform complement of amylases were monitored during seedlingdevelopment. High endoamylase activity was found in taprootsof both species at all samplings. In contrast, exoamylase accumulatedin taproots of alfalfa, but not birdsfoot trefoil, in a patternsimilar to starch accumulation. As in Exp. 1, defoliation increasedendoamylase, but not exoamylase activity in taproots of bothspecies. Taproots of both species contained one major and twominor endoamylase isoforms, but the electrophoretic mobilityof these isoforms differed between species. Activities of allisoforms, as indicated on starch-gel blots, increased in responseto defoliation. These results indicate that defoliation increasesactivity of taproot endoamylases, whose activity is associatedwith taproot starch degradation. Key words: Starch degradation, alfalfa, birdsfoot trefoil, enzymes