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Arginine Metabolism in Developing Soybean Cotyledons: I. Relationship to Nitrogen Nutrition

Barry J. Micallef and Barry J. Shelp
Plant Physiology
Vol. 90, No. 2 (Jun., 1989), pp. 624-630
Stable URL: http://www.jstor.org/stable/4272127
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Arginine Metabolism in Developing Soybean Cotyledons: I. Relationship to Nitrogen Nutrition
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Abstract

The free and protein amino acid composition of Glycine max (L.) Merrill cotyledons was determined for the entire developmental period using high performance liquid chromatography. Arginine constituted 18% of the total protein nitrogen throughout development, and there was a linear arginine nitrogen accumulation rate of 1212 nanomoles per cotyledon per day between 16 and 58 days after anthesis. Arginine and asparagine were major constituents of the free amino acid pool, constituting 14 to 62% and 2 to 41% of the total free amino acid nitrogen, respectively. The urea cycle intermediates, citrulline, ornithine, and arginino-succinate were also detected in the free pool. A comparison of the amino acid composition of cotyledonary protein and of seed-coat exudate suggested that 72% of the cotyledon's arginine requirement is satisfied by in situ biosynthesis, and that 20% of the transformed nitrogen is incorporated into arginine. Also, [1-14C]glutamate and [U-14C]glutamine were fed to excised cotyledons. After 4 hours, 14C was incorporated into protein and released as 14CO2, but none was incorporated into the C-1 and C-6 positions of free and protein arginine, determined using arginine-specific enzyme-linked assays. It is not currently known whether arginine biosynthesis in the cotyledon involves glutamate delivered from the mother plant or glutamate derived in situ.

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