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 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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Spontaneous Phloem Bleeding from Cryopunctured Fruits of a Ureide-Producing Legume <sup><a href="#fn1" rid="fn1" class=" fn">1</a></sup>

J Pate

M Peoples

C Atkins

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 Mg}^{to Ca}^{. Fruit cryopuncture sap became labeled with}^{C following feeding of [}^{C]urea to leaves or adjacent walls of the fruit, of}^CO₂ to the pod gas space, and of [^{C] asparagine or [}^{C]allantoin to leaflets or cut shoots through the xylem. Rates of translocation of}^{C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of}^{C distribution in phloem sap suggested that [}^{C]allantoin was metabolized to a greater extent in its passage to the fruit than was [}^{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 NO₃-nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of ^NO₃ 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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Botany Department, University of Western Australia, Nedlands, W. A. 6009 Australia

^{Supported by funds from the Australian Research Grants Scheme and the Wheat Industry Research Council of Australia.}

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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 Mg}^{to Ca}^{. Fruit cryopuncture sap became labeled with}^{C following feeding of [}^{C]urea to leaves or adjacent walls of the fruit, of}^CO₂ to the pod gas space, and of [^{C] asparagine or [}^{C]allantoin to leaflets or cut shoots through the xylem. Rates of translocation of}^{C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of}^{C distribution in phloem sap suggested that [}^{C]allantoin was metabolized to a greater extent in its passage to the fruit than was [}^{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 NO₃-nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of ^NO₃ 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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