A critical role for disproportionating enzyme in starch breakdown is revealed by a knock-out mutation in Arabidopsis

Plant J. 2001 Apr;26(1):89-100. doi: 10.1046/j.1365-313x.2001.01012.x.


Disproportionating enzyme (D-enzyme) is a plastidial alpha-1,4-glucanotransferase but its role in starch metabolism is unclear. Using a reverse genetics approach we have isolated a mutant of Arabidopsis thaliana in which the gene encoding this enzyme (DPE1) is disrupted by a T-DNA insertion. While D-enzyme activity is eliminated in the homozygous dpe1-1 mutant, changes in activities of other enzymes of starch metabolism are relatively small. During the diurnal cycle, the amount of leaf starch is higher in dpe1-1 than in wild type and the amylose to amylopectin ratio is increased, but amylopectin structure is unaltered. The amounts of starch synthesised and degraded are lower in dpe1-1 than in wild type. However, the lower amount of starch synthesised and the higher proportion of amylose are both eliminated when plants are completely de-starched by a period of prolonged darkness prior to the light period. During starch degradation, a large accumulation of malto-oligosaccharides occurs in dpe1-1 but not in wild type. These data show that D-enzyme is required for malto-oligosaccharide metabolism during starch degradation. The slower rate of starch degradation in dpe1-1 suggests that malto-oligosaccharides affect an enzyme that attacks the starch granule, or that D-enzyme itself can act directly on starch. The effects on starch synthesis and composition in dpe1-1 under normal diurnal conditions are probably a consequence of metabolism at the start of the light period, of the high levels of malto-oligosaccharides generated during the dark period. We conclude that the primary function of D-enzyme is in starch degradation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amylopectin / metabolism
  • Amylose / metabolism
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • DNA, Bacterial / genetics
  • Glycogen Debranching Enzyme System / genetics
  • Glycogen Debranching Enzyme System / metabolism*
  • Immunoblotting
  • Maltose / metabolism
  • Mutagenesis, Insertional
  • Oligosaccharides / metabolism
  • Photoperiod
  • Plant Leaves / genetics
  • Plant Leaves / metabolism
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Starch / biosynthesis
  • Starch / metabolism*


  • DNA, Bacterial
  • Glycogen Debranching Enzyme System
  • Oligosaccharides
  • Plant Proteins
  • T-DNA
  • Maltose
  • Starch
  • Amylose
  • Amylopectin
  • 4 alpha-glucanotransferase