Metabolic changes associated with bud break induced by thidiazuron

Bud break in apple (Golden Delicious,Malus domestica Borkh) was induced by thidiazuron (N-phenyl-N-1,2,3-thidiazol-5-ylurea). In control and thidiazuron-treated shoots, higher amounts of soluble carbohydrates (sorbitol, fructose, glucose, sucrose) and galacturonic acid were found in the phloem, but higher amounts of starch and cell wall polysaccharides, including cellulose and xylose, were found in the xylem. A decrease in soluble carbohydrates and starch in both phloem and xylem was associated with induction of bud break by thidiazuron. However, little change in cell wall polysaccharides was found. Total carbohydrates were higher in the upper than in the lower portion of shoots. The breaking of dormancy by thidiazuron was also associated with an increase in organic acid content and respiration in buds. KCN inhibited bud respiration during all stages of development. Organic acid content was inversely related to carbohydrate content in developing buds. Axes contained more carbohydrates and organic acids than did scales.