Altered regulation of β-amylase activity in mutants of Arabidopsis with lesions in starch metabolism

Altered regulation of β-amylase activity in mutants of Arabidopsis with lesions in starch metabolism

^*Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824
^‡Department of Biochemistry, Michigan State University, East Lansing, MI 48824

Abstract

Three classes of mutants of Arabidopsis thaliana (L.) Heynhold with alterations in starch metabolism were found to have higher levels of leaf amylase activity than the wild type when grown in a 12-hr photoperiod. This effect was dependent upon the developmental stage of the plants and was largely suppressed during growth in continuous light. The various amylolytic activities in crude extracts were separated by electrophoresis in nondenaturing polyacrylamide gels and visualized by activity staining. The increased amylase activity in the mutants was due to an up to 40-fold increase in the activity of an extrachloroplast β-amylase (EC 3.2.1.2). These observations indicate the existence of a regulatory mechanism that controls the amount of β-amylase activity in response to fluctuations in photosynthetic carbohydrate metabolism. It is paradoxical that β-amylase appears to be a highly regulated enzyme, but as yet no physiologically relevant function can be assigned to this enzyme due to the absence of starch in the cytoplasmic compartment of leaf cells.

Footnotes

↵ † Present address: United States Department of Agriculture-Plant Gene Expression Center, 800 Buchanan Street, Albany, CA 94710.
↵ § Present address: Taiwan Forestry Research Institute, 53 Nan-Hai Road, Taipei, Taiwan.
↵ ¶ Present address: Department of Biology, Marietta College, Marietta, OH 45750.
↵ ǁ To whom reprint requests should be addressed.