Changes in enzymic activities of nucleoside diphosphate sugar interconversions during differentiation of cambium to xylem in pine and fir

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Abstract
A protein fraction [precipitate obtained between 40 and 65% (NH4)2SO4 saturation] prepared from cambial cells, differentiating xylem cells and differentiated xylem cells of pine and fir trees contained all the enzymes required for the nucleoside diphosphate sugar interconversions. By using UDP-D-[U-14C]glucose or UDP-D-[U-14C]galactose, UDP-D-[U-14C]glucuronic acid and UDP-D-[U-14C]xylose as substrates, the activities of UDP-D-galactose 4-epimerase (EC 5.1.3.2), UDP-D-glucuronate 4-epimerase (EC 5.1.3.6), UDP-D-xylose 4-epimerase (EC 5.1.3.5), UDP-D-glucose dehydrogenase (EC 1.1.1.22) and UDP-D-glucuronate decarboxylase (EC 4.1.1.35) were measured at different stages of cell-wall development. The specific activites and the activities per cell of these enzymes varied during differentiation of cambium to xylem according to the type of polysaccharide synthesized. Variations were found between the 2 spp. investigated. These data, compared with those obtained in previous work on angiosperms suggest that some control of polysaccharide synthesis operates at the level of the formation of the precursors of pectin and hemicellulose syntheses.