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Amino Acid Metabolism of Pea Leaves

Diurnal Changes and Amino Acid Synthesis from ¹⁵N-Nitrate ¹

^a Department of Biology, Carleton University, Ottawa, Canada K1S 5B6

In the young leaves of pea (Pisum sativum L.) plants, there was a diurnal variation in the levels of amino acids. In the light, total amino nitrogen increased for the first few hours, then stabilized; in the dark, there was a transient decrease followed by a gradual recovery. Asparagine, homoserine, alanine, and glutamine accounted for much of these changes. The incorporation of ¹⁵N into various components of the young leaves was followed after supply of ¹⁵N-nitrate. ¹⁵N appeared most rapidly in ammonia, due to reduction in the leaf, and this process took place predominantly in the light. A large proportion of the primary assimilation took place through the amide group of glutamine, which became labeled and turned over rapidly; labeling of glutamic acid and alanine was also rapid. Asparagine (amide group) soon became labeled and showed considerable turnover. Slower incorporation and turnover were found for aspartic acid, -aminobutyric acid, and homoserine. Synthesis and turnover of all of the amino acids continued at a low rate in the dark. -Aminobutyric acid was the only compound found to label more rapidly in the dark than in the light.

³ To whom reprint requests should be addressed.

¹ Supported by a grant from the National Research Council of Canada.

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