β-Glucan synthetase activities in regenerating protoplasts from carrot suspension cultures

Abstract

The activities of β-glucan synthetases I and II from particulate fractions of protoplast homogenates were compared to the phases of cell wall regeneration in cultivated carrot protoplasts. β-1,4-Glucan synthetase (I), assayed at low UDP-glucose (UDPG) and high Mg 2+ levels showed a lag phase of 15–20 h. The specific activity increased 2-fold during the first 3 days of cultivation. Cultivated carrot cells from the exponential growth period did not exhibit any increase in the activity of the particulate fraction. Inhibitors of RNA and protein synthesis prevented an increase suggesting that enzyme protein synthesis is a prerequisite for this process. β-Glucan synthetase II, presumably producing β-1,3-glucans at high substrate concentrations in the absence of Mg 2+, showed an immediate rise for 20 h, but then declined. The phase of cell wall regeneration was determined by the incorporation of [ 14C]glucose into cellulose.