A starch-accumulating mutant of Arabidopsis thaliana deficient in a chloroplastic starch-hydrolysing enzyme.
The aim of this work was to identify enzymes that participate in the degradation of transitory starch in Arabidopsis. A mutant line was isolated by screening leaves at the end of the night for the presence of starch. The mutant had a higher starch content than the wild-type throughout the diurnal cycle. This accumulation was due to a reduction in starch breakdown, leading to an imbalance between the rates of synthesis and degradation. No reduction in the activity of endo-amylase (alpha-amylase), beta-amylase, starch phosphorylase, maltase, pullulanase or D-enzyme could be detected in crude extracts of leaves of the mutant. However, native PAGE in gels containing amylopectin revealed that a starch-hydrolysing activity, putatively identified as an endo-amylase and present in wild-type chloroplasts, was absent or appreciably reduced in the mutant. This is the first time that a specific enzyme required for starch degradation has been identified in leaves.
Zeeman
S C
SC
John Innes Centre, Norwich Research Park, Colney, Norfolk, UK. zeeman@bbsrc.ac.uk
Northrop
F
F
Smith
A M
AM
Rees
T
T
D000681:Amylases / Q000172:deficiency* / Q000235:genetics / Q000302:isolation & purification; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology; D002940:Circadian Rhythm; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D009154:Mutation; D013213:Starch / Q000378:metabolism*
D013213:Starch; D000681:Amylases