Scientific publications

Activity of sucrose synthase (SS) and the content of starch were studied in the xylem and phloem of two forms of 40-year-old trees of Betula pendula Roth: common silver birch (B. pendula var. pendula) and Karelian birch (B. pendula var. carelica). In order to reveal the initial signs of wood patterning, we used 8-year-old trees of Karelian birch that did not yet exhibit visible deviations from normal growth (trees with unpatterned wood) and those where formation of structural trunk anomalies already commenced (trees with patterned wood). Investigation was conducted during the period of cambial growth: in June growth was active and in July growth was suppressed by weather conditions. In June we found a high SS activity in the xylem of 40-year-old plants of common birch. Retardation of growth of common birch in July was accompanied by the decrease in SS activity in the xylem and by accumulation of starch, especially in the phloem. In 8-year-old trees of Karelian birch with unpatterned wood, the SS activity in the xylem was lower than in common birch trees, while the content of starch in the phloem was higher. In the xylem of trees with patterned wood, the highest activity of SS was approximately 2.5 times lower than in the trees with unpatterned wood. The lower SS activity in the xylem of patterned trunk trees was not associated with starch accumulation in the phloem. We propose that low SS activity during cambial growth reduces sink capacity of xylem tissues, thus leading to a considerable increase in the sucrose content in the phloem, which can alter the program of cell development in the cambial zone of Karelian birch.