¹³CO₂ labeling of carbon atoms in M69⁺ and M41⁺ and their isotopomers through time.

<p>(A) ¹³CO₂ labeling of carbon atoms in trees grown and measured in ambient CO₂ conditions (400 ppm CO₂) in the parent isoprene molecule, as characterized by a decrease in the M69⁺ signal (orange circles) and simultaneous increase in its isotopomers (denoted as sums) as labeled carbons were successively incorporated through time. Total emission (blue circles), sM70⁺ (red downward triangles), sM71⁺ (green triangles), sM72⁺ (yellow squares), sM73⁺ (sea green squares), sM74⁺ (purple diamonds) are represented. (B) ¹³CO₂ labeling of carbon atoms in trees grown and measured at 30°C in ambient CO₂ conditions (400 ppm CO₂) in the 3-C methyl-vinyl isoprene fragment, characterized by a decrease in the M41⁺ signal (light orange dotted downward triangles) with a simultaneous increase in its labeled isotopomers (denoted as sums). Total emission (blue dotted squares), sM42⁺ (pink crossed circles), sM43⁺ (green hexagons), sM44⁺ (yellow diamonds) are represented. Before leaves were exposed to ¹³CO₂ labeling at 1000 seconds, plants were exposed to the same ¹²CO₂ concentrations at which they were grown. The simultaneous labeling of the first carbon in the parent molecule (sM70⁺) and the fragment (sM42⁺) suggest that the first carbon contributing to the synthesis of isoprene comes from the M41⁺ fragment. However, while all of the isoprene molecules show the next two carbons labeled shortly after (sM71⁺ and sM72⁺), the next two carbons on the M41⁺ fragment (sM43⁺ and sM44⁺) are never fully labeled and may result from the incomplete labeling of pyruvate.