PLANT PHYSIOLOGY , Vol 101, Issue 1 73-79, Copyright © 1993 by American Society of Plant Biologists
|
METABOLISM AND ENZYMOLOGY |
Starch Degradation and Distribution of the Starch-Degrading Enzymes in Vicia faba Leaves (Diurnal Oscillation of Amylolytic Activity and Starch Content in Chloroplasts)
C. Ghiena, M. Schulz and H. Schnabl
Institut fur Landwirtschaftliche Botanik, Universitat Bonn, Meckenheimer Allee 176, 5300 Bonn 1, Germany
Subcellular localization of the starch-degrading enzymes in Vicia faba
leaves was achieved by an electrophoretic transfer method through a
starch-containing gel (SCG) and enzyme activity measurements. Total
amylolytic and phosphorolytic activities were found predominantly in the
extrachloroplastic fraction, whereas the debranching enzymes showed
homogenous distribution between stromal and extrachloroplastic fractions.
Staining of end products in the SCG revealed two isoforms of
[alpha]-amylase (EC 3.2.1.1) and very low [beta]-amylase activity (EC
3.2.1.2) in the chloroplast preparation, whereas [alpha]- and
[beta]-amylase exhibited higher activities in the crude extract. However,
it is unclear whether the low [alpha]- and [beta]-amylase activities
associated with the chloroplast are contamination or activities that are
integrally associated with the chloroplast. Study of the diurnal
fluctuation of the starch content and of the amylase activities under a
9-h/15-h photoperiod showed a 2-fold increase of the total amylolytic
activity in the chloroplasts concurrent with the starch degradation in the
dark. No fluctuation was detectable for the extrachloroplastic enzymes. The
possible roles and function of the chloroplastic and extrachloroplastic
hydrolytic enzymes are discussed.