| Abstract: | A comparison was made of the nitrogenous constituents in thesap extracted under vacuum from apple shoots of different ages,as regards changes both with season and in response to fertilizernitrate applied in summer or autumn. Before blossoming the N concentration of the sap changed markedlywith age of shoot, with the values doubling in the samples fromthe proximal half of the 3-year-old wood to the distal 2-year-oldsection, followed by a significant decrease in the 1-year-oldshoot. After blossoming the gradients in sap concentration wereless pronounced but usually the lowest values were found inthe youngest part of the shoot. Fourteen days after a soil application of nitrate in July therewas a marked increase in the concentration of asparagine inthe sap, but only in the 3-year-old section of the shoot. Sevendays later the xylem sap from all parts of the shoot containedincreased levels of asparagine, aspartic acid, and glutamine. No changes in the xylem sap of shoots in response to fertilizerapplied in October were observed until the following April.Then increased amounts of asparagine and glutamine were foundin all sections, with the greatest increase being seen in theyoungest part. It is suggested that this was due to acceleratedmobilization of N reserves into the xylem sap in response togrowth regulators originating in the roots rather than to movementof recently absorbed nutrients. |
