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Contribution of various carbon sources toward isoprene biosynthesis in poplar leaves mediated by altered atmospheric CO2 concentrations.

Trowbridge AM, Asensio D, Eller AS, Way DA, Wilkinson MJ, Schnitzler JP, Jackson RB, Monson RK - PLoS ONE (2012)

Bottom Line: This is the first study to explicitly consider the effects of altered atmospheric CO(2) concentration on carbon partitioning to isoprene biosynthesis.These results suggest that under reduced atmospheric CO(2) availability, more carbon from stored/older carbon sources is involved in isoprene biosynthesis, and this carbon most likely enters the isoprene biosynthesis pathway through the pyruvate substrate.We offer direct evidence that extra-chloroplastic rather than chloroplastic carbon sources are mobilized to increase the availability of pyruvate required to up-regulate the isoprene biosynthesis pathway when trees are grown under sub-ambient CO(2).

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado, United States of America. amy.m.trowbridge@gmail.com

ABSTRACT
Biogenically released isoprene plays important roles in both tropospheric photochemistry and plant metabolism. We performed a (13)CO(2)-labeling study using proton-transfer-reaction mass spectrometry (PTR-MS) to examine the kinetics of recently assimilated photosynthate into isoprene emitted from poplar (Populus × canescens) trees grown and measured at different atmospheric CO(2) concentrations. This is the first study to explicitly consider the effects of altered atmospheric CO(2) concentration on carbon partitioning to isoprene biosynthesis. We studied changes in the proportion of labeled carbon as a function of time in two mass fragments, M41(+), which represents, in part, substrate derived from pyruvate, and M69(+), which represents the whole unlabeled isoprene molecule. We observed a trend of slower (13)C incorporation into isoprene carbon derived from pyruvate, consistent with the previously hypothesized origin of chloroplastic pyruvate from cytosolic phosphenolpyruvate (PEP). Trees grown under sub-ambient CO(2) (190 ppmv) had rates of isoprene emission and rates of labeling of M41(+) and M69(+) that were nearly twice those observed in trees grown under elevated CO(2) (590 ppmv). However, they also demonstrated the lowest proportion of completely labeled isoprene molecules. These results suggest that under reduced atmospheric CO(2) availability, more carbon from stored/older carbon sources is involved in isoprene biosynthesis, and this carbon most likely enters the isoprene biosynthesis pathway through the pyruvate substrate. We offer direct evidence that extra-chloroplastic rather than chloroplastic carbon sources are mobilized to increase the availability of pyruvate required to up-regulate the isoprene biosynthesis pathway when trees are grown under sub-ambient CO(2).

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13CO2 labeling of carbon atoms in M69+ and M41+ and their isotopomers through time.(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.
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pone-0032387-g003: 13CO2 labeling of carbon atoms in M69+ and M41+ and their isotopomers through time.(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.

Mentions: To examine the relative contribution of pyruvate-derived carbons for isoprene synthesis, we analyzed real-time 13CO2 labeling kinetics for both the parent isoprene molecule (M69+) and its 3-C fragment (M41+) for a representative tree grown under ambient CO2 of 400 ppm (Figure 3). By examining simultaneous changes between labeling in the parent molecule (Figure 3A) with changes in the 3-C fragment (Figure 3B), one could obtain a detailed account of the sequence with which labeled carbons were contributed to isoprene synthesis via the 3-C (methyl-vinyl) or 2-C fragments of the fractured isoprene molecule. From Figure 3, there was an immediate and extremely fast increase in the sM42+ and sM70+ signals following 13CO2 labeling. This result confirmed that isoprene emission rate was closely coupled to carbon assimilation and suggested that the addition of labeled carbon to the 3-C fragment had the same consequence for the signal of the parent molecule. This result also supported the conclusions from the labeled carbon data for both M41+ and M69+, which showed that the first labeled carbon transferred into the isoprene pool was recovered as part of the methyl-vinyl subunit. We note that there was a slight increase in the total isoprene emission rate and total amount of 3-C methyl-vinyl isoprene fragment detected when we switched from the 12CO2 source to the 13CO2 source. This effect was detected in all treatments, and was small in magnitude compared to the differences in total emission rates. It is possible that the CO2 concentration was slightly lower than desired in the 13CO2 source, but we were careful to prepare this source according to precise calculations. It is also possible that there was a small decrease in flow rate through the chamber when the sources were changed, and that the flow controller we used was differentially biased toward the presence of 13CO2.


Contribution of various carbon sources toward isoprene biosynthesis in poplar leaves mediated by altered atmospheric CO2 concentrations.

Trowbridge AM, Asensio D, Eller AS, Way DA, Wilkinson MJ, Schnitzler JP, Jackson RB, Monson RK - PLoS ONE (2012)

13CO2 labeling of carbon atoms in M69+ and M41+ and their isotopomers through time.(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.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3285681&req=5

pone-0032387-g003: 13CO2 labeling of carbon atoms in M69+ and M41+ and their isotopomers through time.(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.
Mentions: To examine the relative contribution of pyruvate-derived carbons for isoprene synthesis, we analyzed real-time 13CO2 labeling kinetics for both the parent isoprene molecule (M69+) and its 3-C fragment (M41+) for a representative tree grown under ambient CO2 of 400 ppm (Figure 3). By examining simultaneous changes between labeling in the parent molecule (Figure 3A) with changes in the 3-C fragment (Figure 3B), one could obtain a detailed account of the sequence with which labeled carbons were contributed to isoprene synthesis via the 3-C (methyl-vinyl) or 2-C fragments of the fractured isoprene molecule. From Figure 3, there was an immediate and extremely fast increase in the sM42+ and sM70+ signals following 13CO2 labeling. This result confirmed that isoprene emission rate was closely coupled to carbon assimilation and suggested that the addition of labeled carbon to the 3-C fragment had the same consequence for the signal of the parent molecule. This result also supported the conclusions from the labeled carbon data for both M41+ and M69+, which showed that the first labeled carbon transferred into the isoprene pool was recovered as part of the methyl-vinyl subunit. We note that there was a slight increase in the total isoprene emission rate and total amount of 3-C methyl-vinyl isoprene fragment detected when we switched from the 12CO2 source to the 13CO2 source. This effect was detected in all treatments, and was small in magnitude compared to the differences in total emission rates. It is possible that the CO2 concentration was slightly lower than desired in the 13CO2 source, but we were careful to prepare this source according to precise calculations. It is also possible that there was a small decrease in flow rate through the chamber when the sources were changed, and that the flow controller we used was differentially biased toward the presence of 13CO2.

Bottom Line: This is the first study to explicitly consider the effects of altered atmospheric CO(2) concentration on carbon partitioning to isoprene biosynthesis.These results suggest that under reduced atmospheric CO(2) availability, more carbon from stored/older carbon sources is involved in isoprene biosynthesis, and this carbon most likely enters the isoprene biosynthesis pathway through the pyruvate substrate.We offer direct evidence that extra-chloroplastic rather than chloroplastic carbon sources are mobilized to increase the availability of pyruvate required to up-regulate the isoprene biosynthesis pathway when trees are grown under sub-ambient CO(2).

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado, United States of America. amy.m.trowbridge@gmail.com

ABSTRACT
Biogenically released isoprene plays important roles in both tropospheric photochemistry and plant metabolism. We performed a (13)CO(2)-labeling study using proton-transfer-reaction mass spectrometry (PTR-MS) to examine the kinetics of recently assimilated photosynthate into isoprene emitted from poplar (Populus × canescens) trees grown and measured at different atmospheric CO(2) concentrations. This is the first study to explicitly consider the effects of altered atmospheric CO(2) concentration on carbon partitioning to isoprene biosynthesis. We studied changes in the proportion of labeled carbon as a function of time in two mass fragments, M41(+), which represents, in part, substrate derived from pyruvate, and M69(+), which represents the whole unlabeled isoprene molecule. We observed a trend of slower (13)C incorporation into isoprene carbon derived from pyruvate, consistent with the previously hypothesized origin of chloroplastic pyruvate from cytosolic phosphenolpyruvate (PEP). Trees grown under sub-ambient CO(2) (190 ppmv) had rates of isoprene emission and rates of labeling of M41(+) and M69(+) that were nearly twice those observed in trees grown under elevated CO(2) (590 ppmv). However, they also demonstrated the lowest proportion of completely labeled isoprene molecules. These results suggest that under reduced atmospheric CO(2) availability, more carbon from stored/older carbon sources is involved in isoprene biosynthesis, and this carbon most likely enters the isoprene biosynthesis pathway through the pyruvate substrate. We offer direct evidence that extra-chloroplastic rather than chloroplastic carbon sources are mobilized to increase the availability of pyruvate required to up-regulate the isoprene biosynthesis pathway when trees are grown under sub-ambient CO(2).

Show MeSH
Related in: MedlinePlus