Nitrogen-containing Compounds in the Shoot System of Pisum arvense L. I. Amino Compounds in the Bleeding Saps from Petioles

A technique is described for collecting bleeding saps from the petioles of defoliated plants of the field pea. Analytical studies and 14CO2-feeding experiments indicate that these saps are physically related to the fluids delivered to the xylem by the nodulated root. There is a progressive decrease in the concentration of amino-nitrogen in the bleeding saps recovered from the successive petioles up a stem. This decrease is manifest at any time of the day or night and is evident in all ages of plants. It is suggested that it results from the accumulation of a proportion of the incoming amino-acids and amides in living tissues of the stem. As the stem ages, it appears to become less effective in abstracting materials from the xylem. Stem tissues often show a more intensive uptake of asparagine than of other constituents such as aspartic acid, glutamine, and homoserine. The above studies suggest that much of the nitrogen coming from the root is immediately sequestered by the lower half of the shoot. A similar effect is observed if 14Clabelled bleeding sap is fed to complete, unlabelled shoots via the transpiration stream.