Variations in amounts of carbohydrates, amino acids and adenine nucleotides in mulberry tree (Morus alba L.) stems during transitional phases of growth

Quantitative changes in carbohydrates, amino acids and adenine nucleotides in the stems of mulberry trees (Morus alba L., cv. Shin-ichinose) were followed from spring to early summer and from autumn to early spring. Both ATP and ADP content of stems increased before bud break, whereas the content of sucrose, the most abundant sugar among the stem carbohydrates, decreased. The sucrose content fell to its lowest value at the beginning of May, and then increased rapidly, whereas the starch content decreased suggesting consumption of reserve carbohydrate and simultaneous accumulation of current photosynthate. This was confirmed by studies in which reserve carbohydrates were labeled with (14)CO(2). Proline content of stems increased from the time of leaf shedding until early spring. Although it was the most abundant amino acid at the time of bud break, proline rapidly decreased as new shoots developed and was hardly detectable by the beginning of May. The asparagine and arginine contents increased transiently following bud break, and then decreased toward summer. Transient increases in glutamine and arginine were noted at the time of leaf shedding.