Carbon isotope composition of intermediates of the starch-malate sequence and level of the crassulacean acid metabolism in leaves of Kalanchoe blossfeldiana Tom Thumb |
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Authors: | Eliane Deleens Jeannine Garnier-Dardart Orlando Queiroz |
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Institution: | (1) Laboratoire de Physiologie Cellulaire Végétale, Associé au C.N.R.S., dépendant de l'Université de Paris XI, Centre d'Orsay, Bât. 430, F-91405 Orsay Cedex, France;(2) Laboratoire du Phytotron, C.N.R.S., F-91190 Gir sur Yvette, France |
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Abstract: | Isotype analyses were performed on biochemical fractions isolated from leaves of Kalanchoe blossfeldiana Tom Thumb. during aging under long days or short days. Irrespective of the age or photoperiodic conditions, the intermediates of the starch-malate sequence (starch, phosphorylated compounds and organic acids) have a level of 13C higher than that of soluble sugars, cellulose and hemicellulose. In short days, the activity of the crassulacean acid metabolism pathway is predominant as compared to that of C3 pathway: leaves accumulate organic acids, rich in 13C. In long days, the activity of the crassulacean acid metabolism pathway increases as the leaves age, remaining, however, relatively low as compared to that of C3 pathway: leaves accumulate soluble sugars, poor in 13C. After photoperiodic change (long daysshort days), isotopic modifications of starch and organic acids suggest evidence for a lag phase in the establishment of the crassulacean acid metabolism pathway specific to short days. The relative proportions of carbon from a C3-origin (RuBPC acitivity as strong discriminating step, isotope discrimination in vivo=20) or C4-origin (PEPC activity as weak discriminating step, isotope discrimination in vivo=4) present in the biochemical fractions were calculated from their 13C values. Under long days, 30 to 70% versus 80 to 100% under short days, of the carbon of the intermediates linked to the starch-malate sequence, or CAM pathway (starch, phosphorylated compounds and organic acids), have a C4-origin. Products connected to the C3 pathway (free sugars, cellulose, hemicellulose) have 0 to 50% of their carbon, arising from reuptake of the C4 from malate, under long days versus 30 to 70% under short days.Abbreviations CAM
crassulacean acid metabolism
- CAM pathway
pathway with malate accumulation by -carboxylation of PEP, arising from glycolysis of starch (starch-malate sequence)
- C3-metabolism
metabolism with primary carbon fixed by the Calvin and Benson pathway (C3-origin)
- C4-metabolism
metabolism with primary carbon fixed by the Hatch and Slack pathway (C4-origin)
- C3-pathway
pathway with RuBPC activity and the Calvin and Benson pathway, irrespective of the CO2-source, atmospheric or reuptake of the C4 from malate
- 13C()=(Rsample-RPDR)103/RPDB where PDB
Pee Dee belemnite (belemnite from the Pee Dee formation, South Carolina) and R=13C/12C
- D
isotope discrimination
- PEP
phosphoenolpyruvate
- PEPC (EC 4.1.1.31)
PEP carboxylase
- PGA
phosphoglyceric acid
- Py.di-PK (EC 2.7.9.1)
pyruvate, Pi-dikinase
- RuBP
ribulose bisphosphate
- RuBPC (EC 4.1.1.39)
RuBP carboxylase
- SD
short days
- LD
long days |
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Keywords: | Crassulacean acid metabolism 13C/14C ratio Malate reuptake Photoperiodism |
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