In this study, our goal was to evaluate the role of starch debranching enzymes in the determination of the structure of amylopectin. We screened mutant populations of Arabidopsis for plants with alterations in the structure of leaf starch by using iodine staining. The leaves of two mutant lines stained reddish brown, whereas wild-type leaves stained brownish black, indicating that a more highly branched polyglucan than amylopectin was present. The mutants were allelic, and the mutation mapped to position 18.8 on chromosome 1. One mutant line lacked the transcript for a gene with sequence similarity to higher plant debranching enzymes, and both mutants lacked a chloroplastic starch-hydrolyzing enzyme. This enzyme was identified as a debranching enzyme of the isoamylase type. The loss of this isoamylase resulted in a 90% reduction in the accumulation of starch in this mutant line when compared with the wild type and in the accumulation of the highly branched water-soluble polysaccharide phytoglycogen. Both normal starch and phytoglycogen accumulated simultaneously in the same chloroplasts in the mutant lines, suggesting that isoamylase has an indirect rather than a direct role in determining amylopectin structure.

biosynthesis, gene, degradation, branching enzyme, Pisum sativum L, zea-mays, maize, amylopectin, endosperm, isoforms

• Compound ID: 21233
  

  {{{-a-D-Glcp-(1-4)-}}}?%a-D-Glcp-(1-6)-+ | -4)-a-D-Glcp-(1-

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  Structure type: structural motif or average structure
  Trivial name: glycogen, starch, amylopectin, amylopectin, phytoglycogen, amylopectin, amylose, amylose, amylopectin
  Compound class: glucan
  Reference(s) to other database(s): GTC:G68717OT
  
   
  
  Arabidopsis, Arabidopsis dbe1-1, Arabidopsis dbe1-2
  CSDB ID 60776 (all data & tools)