Bleeding sap N
Springer Online Journal Archives 1860-2000
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Summary The nitrogenous compounds in the xylem (bleeding) sap of lines of field-grownPhaseolus vulgaris L., known to vary in N2 fixation and yield, were measured during growth with and without N fertilizer. Forty nine-67% of the total sap N was in the form of nitrate in fertilized plants, with low amounts of the ureides, allantoin and allantoic acid (4–12%). Ureides contributed between 17 and 38% to the total sap N of non-fertilized plants, with nitrate generally comprising less than 40%. Among the nine lines grown without fertilizer there were significant differences in the % of the sap N as ureides and also in the total μmol N ml−1 sap. The ASN/GLN ratio (mol/mol) was greater in sap collected from the two parental lines given fertilizer compared with non-fertilized plants. However the actual ratio varied between the parental lines. Together the two amides generally comprised between 43–62% of the amino-N in sap samples from the two parental lines with or without N fertilizer. For each N treatment (fertilized or non-fertilized) there were no obvious differences in sap composition between the high N2 fixing lines and the low N2 fixing lines. However there was generally a positive relationship between the rate of N translocation (total N concn. ml−1 sap x rate of exudation) and the ranking of the lines on the basis of higher N2 fixation rates (acetylene reduction), which was to a large extent independent of the source of N available to the plant.
Type of Medium: