Changes in enzyme activities involved in formation and interconversion of UDP-sugars during the cell cycle in a synchronous culture of Catharanthus roseus

Changes in the activities of enzymes involved in UDP-sugar formation [UDP-glucose pyrophosphorylase (EC 2.7.7.9), sucrose synthase (EC 2.4.1.13) and UDP-glucuronic acid pyrophosphorylase (EC 2.7.7.44)], and interconversion [UDP-glucuse 4-epimerase (EC 5.1.3.2), UDP-glucose dehydrogenase (EC 1.1.1.22), UDP-glucuronic acid decarboxylase (EC 4.1.1.35) and UDP-xylose 4-epimerase (EC 5.1.3.5)] were investigated during the cell cycle in a synchronous culture of Catharanthus roseus (L.) G. Don. The specific activities of UDP-glucose pyrophosphorylase and UDP-glucose 4-epimerase increased in the G2 phase before the first cell division, and those of sucrose synthase, UDP-glucose dehydrogenase and UDP-glucuronic acid pyrophosphorylase increased in the G1 phase after the first cell division. However, during the cell cycle, UDP-glucuronic acid decarboxylase and UDP-xylose 4-epimerase did not change significantly in their specific activities. Changes in enzyme activities are discussed in relation to those reported previously for cell wall composition (S. Amino et al. 1984. Physiologia Plantarum 60: 326–332).