NITROGENOUS METABOLISM OF PYRUS MALUS L.: III THE PARTITION OF NITROGEN IN THE LEAVES, ONE AND TWO YEAR BRANCH GROWTH AND NON-BEARING SPURS THROUGHOUT A YEAR'S CYCLE

Abstract

Total N, total water-soluble N, and the non-protein fractions (ammonia N, nitric N, mono- and di-amino N, free and also combined amide N, humin N and "rest" N) were determined in the parts of a Stayman Winesap tree. Samples were collected at 11 physiologically significant periods between June 18, 1923, and June 11, 1924. The total N and all the partition fractions both of the leaves and of the "woody" grow,th decreases when growth is very rapid. The total water-soluble N, the non-protein N, and the amino N parallel the total N in all tissues throughout the cycle, but the amide N and "rest" N tend to vary inversely with the total N and the other fractions mentioned. In the leaves, the fluctuations of the water-soluble, the non-protein N, and also of the free and combined amino N fractions vary inversely to their course in the branch growth throughout the year. Amino N appears to be connected with protein synthesis and the "rest" N in protein degradation, but there is no evidence that amino acids act as catalyzers in accelerating the rate of growth. During bud swelling the reserve proteins are transported to the actively growing parts chiefly as amino acids. The phenomena of autumnal migration of N from the leaves to the branches was established for this species. Storage of N in the autumn is mainly in the 1 and 2 yr. branch growths. In the aerial parts nitric N (nitrates) was found only just as the buds were opening. The water-soluble N and ammonia N are very small throughout the cycle. The importance of the role in metabolism of the "rest" N compounds is pointed out, a knowledge of the nature of which is highly desirable. N equilib-rium is just about maintained by the application of 5 lbs. of NaNO3 to a 15 yr. old Stayman Winesap tree growing in sod.