期刊
PLANT JOURNAL
卷 61, 期 1, 页码 122-133出版社
WILEY
DOI: 10.1111/j.1365-313X.2009.04040.x
关键词
NADP-dependent malic enzyme (NADP-ME); NAD-dependent malic enzyme (NAD-ME); phosphoenolpyruvate carboxykinase (PEPCK); amino acid metabolism; C-4 photosynthesis; Arabidopsis
资金
- BBSRC
- Leverhulme Trust
- Deutsche Forschungsgemeinschaft
- Max-Planck Gesellschaft
- Biotechnology and Biological Sciences Research Council [P19982] Funding Source: researchfish
Cells associated with veins of petioles of C-3 tobacco possess high activities of the decarboxylase enzymes required in C-4 photosynthesis. It is not clear whether this is the case in other C-3 species, nor whether these enzymes provide precursors for specific biosynthetic pathways. Here, we investigate the activity of C-4 acid decarboxylases in the mid-vein of Arabidopsis, identify regulatory regions sufficient for this activity, and determine the impact of removing individual isoforms of each protein on mid-vein metabolite profiles. This showed that radiolabelled malate and bicarbonate fed to the xylem stream were incorporated into soluble and insoluble material in the mid-vein of Arabidopsis leaves. Compared with the leaf lamina, mid-veins possessed high activities of NADP-dependent malic enzyme (NADP-ME), NAD-dependent malic enzyme (NAD-ME) and phosphoenolpyruvate carboxykinase (PEPCK). Transcripts derived from both NAD-ME, one PCK and two of the four NADP-ME genes were detectable in these veinal cells. The promoters of each decarboxylase gene were sufficient for expression in mid-veins. Analysis of insertional mutants revealed that cytosolic NADP-ME2 is responsible for 80% of NADP-ME activity in mid-veins. Removing individual decarboxylases affected the abundance of amino acids derived from pyruvate and phosphoenolpyruvate. Reducing cytosolic NADP-ME activity preferentially affected the sugar content, whereas abolishing NAD-ME affected both the amino acid and the glucosamine content of mid-veins.
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