Regulation of malic-acid metabolism in Crassulacean-acid-metabolism plants in the dark and light: In-vivo evidence from 13C-labeling patterns after 13CO2 fixation |
| |
| Authors: | C B Osmond J A M Holtum M H O'Leary C Roeske O C Wong R E Summons P N Avadhani |
| |
| Institution: | (1) Plant Environmental Biology Group, Research School of Biological Sciences, Australian National University, P.O. Box 475, 2601 Canberra, A.C.T., Australia;(2) Department of Chemistry and Biochemistry, University of Wisconsin, 53706 Madison, WI, USA;(3) Present address: Department of Botany, Duke University, 21106 Durham, NC, USA;(4) Present address: Department of Agronomy, Waite Institute for Agricultural Research, University of Adelaide, 5064 Glen Osmond, S.A., Australia;(5) Present address: Department of Plant Biology, University of Illinois, 61801 Urbana, IL, USA;(6) Present address: Division of Continental Geology, Bureau of Mineral Resources, Box 378, 2601 Canberra, A.C.T., Australia;(7) Present address: Botany Department, National University of Singapore, Kent Ridge, 511, Singapore |
| |
| Abstract: | The labeling patterns in malic acid from dark 13CO2 fixation in seven species of succulent plants with Crassulacean acid metabolism were analysed by gas chromatography-mass spectrometry and 13C-nuclear magnetic resonance spectrometry. Only singly labeled malic-acid molecules were detected and on the average, after 12–14 h dark 13CO2 fixation the ratio of 4-13C] to 1-13C] label was 2:1. However the 4-C carboxyl contained from 72 to 50% of the label depending on species and temperature. The 13C enrichment of malate and fumarate was similar. These data confirm those of W. Cockburn and A. McAuley (1975, Plant Physiol. 55, 87–89) and indicate fumarase randomization is responsible for movement of label to 1-C malic acid following carboxylation of phosphoenolpyruvate. The extent of randomization may depend on time and on the balance of malic-acid fluxes between mitochondria and vacuoles. The ratio of labeling in 4-C to 1-C of malic acid which accumulated following 13CO2 fixation in the dark did not change during deacidification in the light and no doubly-labeled molecules of malic acid were detected. These results indicate that further fumarase randomization does not occur in the light, and futile cycling of decarboxylation products of 13C] malic acid (13CO2 or 1-13C]pyruvate) through phosphoenolpyruvate carboxylase does not occur, presumably because malic acid inhibits this enzyme in the light in vivo. Short-term exposure to 13CO2 in the light after deacidification leads to the synthesis of singly and multiply labeled malic acid in these species, as observed by E.W. Ritz et al. (1986, Planta 167, 284–291). In the shortest times, only singly-labeled 4-13C]malate was detected but this may be a consequence of the higher intensity and better detection statistics of this ion cluster during mass spectrometry. We conclude that both phosphoenolpyruvate carboxylase (EC 4.1.1.32) and ribulose-1,5-biphosphate carboxylase (EC 4.1.1.39) are active at this time.Abbreviations CAM
Crassulacean acid metabolism
- GCMS
gas chromatography-mass spectrometry
- MS
mass spectrometry
- NMR
nuclear magnetic resonance spectrometry
- PEP
phosphoenolpyruvate
- RuBP
ribulose 1,5-bisphosphate |
| |
| Keywords: | Carbon dioxide fixation (dark) Crassulacean acid metabolism Fumarase Malic acid Phosphoenolpyruvate carboxylase Ribulose-1 5-bisphosphate carboxylase |
| 本文献已被 SpringerLink 等数据库收录！ |
|
