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 N 2 . 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 Mg 2+ to Ca 2+ . Fruit cryopuncture sap became labeled with 14 C following feeding of ( 14 C)urea to leaves or adjacent walls of the fruit, of 14 CO 2 to the pod gas space, and of ( 14 C) asparagine or ( 14 C)allantoin to leaflets or cut shoots through the xylem. Rates of translocation of 14 C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of 14 C distribution in phloem sap suggested that ( 14 C)allantoin was metabolized to a greater extent in its passage to the fruit than was ( 14 C) asparagine. Amino acid:ureide:nitrate ratios (nitrogen weight basis) of NO 3 -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 NO 3 -nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of 15 NO 3 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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