Figure 2.

Amino acid enrichment and turnover in the leaves of Arabidopsis plants labeled with ¹³CO₂. Arabidopsis seedlings were grown in the enclosure with 99 atom% ¹³CO₂ for three weeks from seed then chased with ambient air (containing ¹²CO₂) for different durations before sampling for amino acid analyses using GC-MS. Data from 3 amino acids, cysteine, asparagine and arginine, were not shown. The half-lives of amino acids were calculated by non-linear regression assuming a simple exponential decay process with no plateau. The percent ¹³C enrichment is given as the number listed parenthetically above the bars for each amino acid. A graph inside this figure shows the diminution of a heavy fragment ion (m/z 163) and emergence of the light fragment ion (m/z 160) of the derivatized [¹³C]-labeled aspartic acid (Asp) during the isotopic dilution period. The elemental composition of this specific fragment ion was determined to be C₆H₁₀NO₄; but in the fragment only C₃H₄N₁ originated from the amino acid and the remainder of the elements were from the derivatization reagent.