In poplar wood starch is converted to soluble sugars, mostly sucrose,
raffinose, stachyose, and maltose, at the beginning of the dormant sea
son. In a first attempt to understand the mechanism of starch degradat
ion during this period the following enzymes were extracted and quanti
fied in weekly intervals: total amylase, or-amylase (EC 3.2.1.1), star
ch phosphorylase (EC 2.4.1.1), debranching enzyme (EC 3.2.1.41), D-enz
yme (EC 2.4. 1.25), maltase (EC 3.2.1.20), maltose phosphorylase (EC 2
.4.1.8), starch synthase (EC 2.4.1.21), and ADPGlcPPase (EC 2.7.7.27).
Maximum extractable activity of the starch-degrading enzymes was obse
rved during the phase of rapid starch decline in October. Later in the
year, only D-enzyme was closely correlated with changes of the starch
content. Native PAGE and activity staining revealed that only four of
13 amylolytic bands were associated with periods of starch decline. T
wo of these bands were detectable also at low temperature and at a sli
ghtly alkaline pH. They were not inhibited by maltose. It is suggested
that these amylase isoforms are located in amyloplasts and take part
in starch degradation. The activities of enzymes involved in starch sy
nthesis, ADPGlcPPase and starch synthase also increased in fall. This
observation is consistent with the occurrence of high temperature indu
ced starch resynthesis during the dormant season.