Amino acid metabolism in plant leaf

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Abstract
Sunflower leaf discs were fed with several 15N-labeled nitrogenous compounds such as nitrate, nitrite, hydroxylamine, ammonium, glutamine, glutamic acid, aspartic acid, γ-aminobutyric acid, alanine, glycine and leucine under light and dark conditions. The incorporation of UN into amino acids extracted from the leaf discs was studied. 15N from the inorganic compounds was most actively incorporated into the amido-group of glutamine, the 15N content of which was considerably higher in the dark than that in the light. This result suggests that inorganic nitrogen is incorporated into amino acids after being reduced to ammonium. The application of 15N-labeled amino acids brought about a characteristic UN distribution pattern in each case. The incorporation of 15N into serine decreased remarkably in the dark except for the application of glycine, indicating that the introduction of the aminogroup into serino strictly depends upon tight. Based on the present experiment, a speculative scheme. of nitrogen flow. from nitrate to amino acids will be presented.