ENZYMES OF STARCH METABOLISM IN POPLAR WOOD DURING FALL AND WINTER

In poplar wood starch is converted to soluble sugars, mostly sucrose, raffinose, stachyose, and maltose, at the beginning of the dormant season. In a first attempt to understand the mechanism of starch degradation during this period the following enzymes were extracted and quantified in weekly intervals: total amylase, or-amylase (EC 3.2.1.1), starch phosphorylase (EC 2.4.1.1), debranching enzyme (EC 3.2.1.41), D-enzyme (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 observed 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. Two of these bands were detectable also at low temperature and at a slightly 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 synthesis, ADPGlcPPase and starch synthase also increased in fall. This observation is consistent with the occurrence of high temperature induced starch resynthesis during the dormant season.