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. 1984 Mar;74(3):499–505. doi: 10.1104/pp.74.3.499

Spontaneous Phloem Bleeding from Cryopunctured Fruits of a Ureide-Producing Legume 1

John S Pate 1, Mark B Peoples 1, Craig A Atkins 1
PMCID: PMC1066715  PMID: 16663451

Abstract

The vasculature of the dorsal suture of cowpea (Vigna unguiculata [L.] Walp) fruits bled a sugar-rich exudate when punctured with a fine needle previously cooled in liquid N2. Bleeding continued for many days at rates equivalent to 10% of the estimated current sugar intake of the fruit. A phloem origin for the exudate was suggested from its high levels (0.4-0.8 millimoles per milliliter) of sugar (98% of this as sucrose) and its high K+ content and high ratio of Mg2+ to Ca2+. Fruit cryopuncture sap became labeled with 14C following feeding of [14C]urea to leaves or adjacent walls of the fruit, of 14CO2 to the pod gas space, and of [14C] asparagine or [14C]allantoin to leaflets or cut shoots through the xylem. Rates of translocation of 14C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of 14C distribution in phloem sap suggested that [14C]allantoin was metabolized to a greater extent in its passage to the fruit than was [14C] asparagine. Amino acid:ureide:nitrate ratios (nitrogen weight basis) of NO3-fed, non-nodulated plants were 20:2:78 in root bleeding xylem sap versus 90:10:0.1 for fruit phloem sap, suggesting that the shoot utilized NO3-nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of 15NO3 to roots substantiated this conclusion. The amino acid:ureide ratio (nitrogen weight basis) of root xylem sap of symbiotic plants was 23:77 versus 89:11 for corresponding fruit phloem sap indicating intense metabolic transfer of ureide-nitrogen to amino acids by vegetative parts of the plant.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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