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 thepetioles of defoliated plants of the field pea. Analytical studiesand ¹⁴CO₂-feeding experiments indicate that these saps are physicallyrelated to the fluids delivered to the xylem by the nodulatedroot. There is a progressive decrease in the concentration ofamino-nitrogen in the bleeding saps recovered from the successivepetioles up a stem. This decrease is manifest at any time ofthe day or night and is evident in all ages of plants. It issuggested that it results from the accumulation of a proportionof the incoming amino-acids and amides in living tissues ofthe stem. As the stem ages, it appears to become less effectivein abstracting materials from the xylem. Stem tissues oftenshow a more intensive uptake of asparagine than of other constituentssuch as aspartic acid, glutamine, and homoserine. The abovestudies suggest that much of the nitrogen coming from the rootis immediately sequestered by the lower half of the shoot. Asimilar effect is observed if ¹⁴Clabelled bleeding sap is fedto complete, unlabelled shoots via the transpiration stream.