Qualitative and quantitative changes in nitrogenous compounds in senescing leaf and bark tissues of the apple

Quantitative and qualitative changes in proteins and ethanol-soluble nitrogen were followed in senescing leaf and bark tissues of ‘Golden Delicious’ apple trees (Malus domestica Borkh.). While senescing leaves lost 46% of their proteins, total bark protein increased 240% during senescence. However, the protein nitrogen gain in bark tissue was about the same as the protein nitrogen loss in leaf tissue per unit fresh weight of tissues. The pattern of bark protein accumulation appears to be gradual from early August to November and sequential from lower to higher molecular weight species of proteins. The final electrophoretic profile of total bark proteins was established at the later stages of senescence. By late November, 89% of the nitrogen in the bark tissue was found in proteins with 11% in the ethanol-soluble fractions. The total protein content of dormant bark tissue was 3.5% per gram dry tissue. Fractionation of the total bark proteins by DEAE-cellulose chromatography indicated that the final upsurge of bark proteins observed in November was associated primarily with one group of proteins (Peak III).