Developmental lignification and seasonal variation in β-glucosidase and peroxidase activities in xylem of Scots pine, Norway spruce and silver birch

We examined the relationship between β-glucosidase and peroxidase activities and xylem lignification in the stems of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth) during the 1999 growing season. Examination of stem cross sections stained with safranin and Alcian blue for lignin and cellulose, respectively, indicated that radial growth of pine and spruce xylem began in late May, whereas the growth of birch xylem was initiated 2 weeks later. Lignification began soon after thickening of the newly formed cell walls, i.e., upon deposition of cellulose. Hydrolysis of the synthetic β-glucosidase substrate p-nitrophenyl-β-O-D-glucopyranoside was correlated with radial growth and lignification in the xylem of both conifers, but the relationship between lignification and the hydrolysis of coniferin by β-glucosidase was not obvious. β-Glucosidase activities in the xylem of silver birch were low and did not correlate with growth or lignification with either substrate. An increase in peroxidase activity was detected at the initiation of growth and lignification in the conifers and during growth and lignification in silver birch, but high peroxidase activities were also measured outside the growth period during late autumn, winter and early spring.