The content of nitrogen and free amino acids in the spurs of annually and biennial bearing apple trees and the problem of their relation to flower-bud initiation

Abstract

The cluster bases (bourses) in each case had a higher content of total nitrogen and both absolute and relative soluble organic nitrogen than the new secondary growth of cluster bases on trees both with fruit and without fruit than new spurs on trees with fruit. This higher content of total and soluble nitrogen is primarily a feature of the organ and has no connection with the initiation of flower buds. The secondary growth of cluster bases on the trees with fruit never had a significantly higher content of soluble nitrogen than the new secondary growth of cluster bases and new growth of spurs on trees without fruit. In all apple varieties observed the same qualitative pattern of free amino acids and amides was determined and a similar ratio of free amino acids and amides in the corresponding axial parts. The highest amount of free amino acids and amides—especially asparagine and arginine—was determined in the cluster bases. Arginine was accumulated in large quantities in the cluster bases much earlier than in the secondary growth of cluster bases or in the new growth of spurs. An accumulation of arginine and asparagine occurred in the cluster bases even when the supply of nitrogen was insufficient, in the secondary growths of cluster bases, however, their content was very low during nitrogen deficiency. The content of glutamine and sometimes threonine in cluster bases with fruit was also considerably increased. There was more glutamic acid, glutamine and sometimes threonine too in younger axils than in older ones already lignified.