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Investigation of phosphoeno/pyruvate carboxylase (PEPCase) in Mesembryanthemum crystallinum L. in C 3 and CAM photosynthetic states
Author(s) -
SLOCOMBE S. P.,
WHITELAM G. C.,
COCKBURN W.
Publication year - 1993
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1993.tb00886.x
Subject(s) - mesembryanthemum crystallinum , crassulacean acid metabolism , phosphoenolpyruvate carboxylase , biology , biochemistry , gene isoform , protein subunit , pyruvate carboxylase , isozyme , photosynthesis , rubisco , enzyme , botany , gene
When exposed to osmotic stress, Mesembryanthemum crystallinum plants switch from C 3 to CAM photosynthesis. Phospho enol pyruvate carboxylase (PEPCase) is a key enzyme in CAM plants, being responsible for the initial fixation of CO 2 . In C 3 plants the enzyme has been shown to be involved in the replenishing of TCA cycle intermediates and in the operation of stomatal guard cells. Multiple PEPCase isoforms were observed in C 3 ‐performing leaves with four isoelectric points of 5.2, 5.5, 5.6 and 5.9 and four apparent subunit molecular masses of 105, 108, 113 and 116 kDa. In some instances, subunits of different size possessed exactly the same pI. The induction of CAM led to the predominance of a new isoform of pI 6.5 with subunit molecular mass of 108 kDa, but in addition, changes were observed in some of the isoforms present in the C 3 plant. PEPCase subunits were purified from the C 3 and CAM forms of M. crystallinum and subjected to pep‐tide mapping. Two distinct though similar sets of maps were obtained, one from the CAM isoform (pI 6.5) and C 3 ‐associated subunits of pi 5.9 and another for C 3 subunits of pI 5.2 and 5.5. It was inferred from these data that the C 3 isoforms expressed in the leaf were derived from at least two genes. The C 3 isoform (pI 5.9) showing greatest similarity to the CAM isoform in terms of peptide mapping also increased in response to salt stress. It is speculated that the CAM isoform may have evolved from this enzyme.