Pathways of Translocation and Metabolic Conversions of Root-Absorbed 14c (U) L-Glutamic Acid in Tomato Plants

Die, J. Van

doi:10.1111/j.1438-8677.1963.tb00120.x

Cited by 20 publications

(1 citation statement)

References 12 publications

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“…Mature leaves (vigorously transpiring) receive most of this xylemborne nitrogen (8,19). Nitrogen levels stabilize in fully-expanded leaves (4) and therefore much of the incoming nitrogen must be reexported.…”

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Transport, Metabolism, and Redistribution of Xylem-Borne Amino Acids in Developing Pea Shoots

Urquhart

Joy²

1982

Plant Physiol.

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Amino acid metabolism and transport was investigated in the leaves of 3-week-old nonnodulated seedlings of Pisum sativum L. Xylem sap entering the shoot contained nitrate (about 5 millimolar), and amino compounds (11 millimolar) of which 70% was asparagine plus glutamine; aspartate and homoserine were also present. Mature leaves showed stable nitrogen levels and incoming nitrogen was redistributed to growing leaves. Younger leaves, still enclosed in the stipules, showed negligible rates of transpiration, suggesting that most of their nitrogen must arrive in the phloem."C-Labeled amides and amino acids were supplied to detached shoots through the xylem, and metabolism and redistribution were followed over 12 hours in light. Asparagine entering mature leaves was reexported directly to young leaves, with relatively little metabolic conversion. Substantial amounts of glutamine were converted to glutamate, which was exported (with unchanged amide) with little further conversion. The pattern of redistribution was confirmed when "C-labeled amino acids were applied directly to the under surface of mature leaves. Labeled compounds were found in the phloem exudate from treated leaves, and the composition resembled the pattern of labeling in the compounds arriving in the young developing leaves. from mature to developing leaves was not followed in detail, nor were labeled compounds recovered in the developing leaves identified. Export from the mature leaves of label from amino acids (applied as tracers to the leaf surface) has been demonstrated in several plants (1 1, 20, 22).In P. sativum seedlings, the xylem sap contains a mixture of nitrate and organic nitrogenous compounds, mainly asparagine and glutamine, but also homoserine, asparate, and a few other amino acids (4,25). Experiments with lWN-labeling showed that pea leaves utilize the nitrogen from nitrate and from asparagine and glutamine for further amino acid metabolism (5). In these pea seedlings, the young leaves of the vegetative apex are enclosed within the stipules of the next oldest, expanding leaves, and there is little transpirational flow to the apical leaves. Young pea leaves are therefore a useful system in which to study redistribution of nitrogen from the mature leaves.Uptake and redistribution of 14C-labeled amides, the major nitrogenous compounds in the xylem of pea (25), was followed in mature, expanding, and immature leaves of nonnodulated plants over 12 h in the light, after supply to the shoot in the transpiration stream. Movement of amino acids from mature leaves to immature leaves and other parts of the plant was investigated by application of 14C-labeled amino acids to the lower surface of mature leaves.Nitrogen required for growth of plant shoots is transported from the roots via the xylem as a mixture of nitrate and organic nitrogen, the proportions varying with species and conditions (17). Mature leaves (vigorously transpiring) receive most of this xylemborne nitrogen (8,19). Nitrogen levels stabilize in fully-expanded leaves (4) an...

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Transport, Metabolism, and Redistribution of Xylem-Borne Amino Acids in Developing Pea Shoots

Urquhart

Joy²

1982

Plant Physiol.

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Architecture of the Internodal Xylem of Tomato (Solanum Lycopersicum) With Reference to Longitudinal and Lateral Transfer

Schoot

Bel

1989

American J of Botany

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The anatomical organization of the internodal tomato xylem was studied with the goal to relate xylem architecture, longitudinal flow, and lateral solute displacement in the stem. On account of a vessel member inventory, obtained by maceration, two vessel types were reconstructed distinct in diameter, morphology, and location. Type I: wide vessels (diam 50–160 μm), with a relatively constant diameter and low horizontal perforation rims, the widest (in the main areas) often extending over more than one internode in length. Type II: narrow vessels (diam 10–50 μm), with occasional vessel dichotomy, average length 5 mm, an irregular diameter, and a meandering vessel lumen due to many oblique and side positions of the perforations. The axial symplast units consisting of various intergrading elements, communicate with the vessel system via sheaths of axial contact cells with a high reducing capacity. The radial symplast units communicate with the vessels via radial contact cells at windows in the axial sheaths. The vessel/symplast interface of the axial and radial symplasts is in the proportion 65:35. The excessive metabolic activity and the high tangential pit frequency of the ray cells mark the rays as the conduits for symplastic xylem‐to‐phloem transfer. Radially fused intercellular spaces in the rays suggest that radial apoplastic solute transfer may also occur.

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Exchange of Solutes between Phloem and Xylem and Circulation in the Whole Plant

Pate¹

1975

Transport in Plants I

116

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Pathways of Translocation and Metabolic Conversions of Root-Absorbed 14c (U) L-Glutamic Acid in Tomato Plants

Cited by 20 publications

References 12 publications

Transport, Metabolism, and Redistribution of Xylem-Borne Amino Acids in Developing Pea Shoots

Transport, Metabolism, and Redistribution of Xylem-Borne Amino Acids in Developing Pea Shoots

Architecture of the Internodal Xylem of Tomato (Solanum Lycopersicum) With Reference to Longitudinal and Lateral Transfer

Exchange of Solutes between Phloem and Xylem and Circulation in the Whole Plant

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