Premium
Competing carboxylases: circadian and metabolic regulation of Rubisco in C 3 and CAM Mesembryanthemum crystallinum L.
Author(s) -
DAVIES B. N.,
GRIFFITHS H.
Publication year - 2012
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.1365-3040.2012.02483.x
Subject(s) - mesembryanthemum crystallinum , crassulacean acid metabolism , rubisco , phosphoenolpyruvate carboxylase , biology , photosynthesis , pyruvate carboxylase , biochemistry , enzyme
The temporal co‐ordination of ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPc) activities by Mesembryanthemum crystallinum L. in C 3 and crassulacean acid metabolism (CAM) modes was investigated under conventional light‐dark (LD) and continuous light (LL) conditions. When C 3 , net CO 2 assimilation rate increased during each subjective night under LL with maximum carboxylation unrelated to Rubisco activation state. The CAM circadian rhythm of CO 2 uptake was more pronounced, with CO 2 assimilation rate maximal towards the end of each subjective night. In vivo and in vitro techniques were integrated to map carboxylase enzyme regulation to the framework provided by CAM LL gas exchange activity. Rubisco was activated in vitro throughout each subjective dark period and consistently deactivated at each subjective dawn, similar to that observed at true dawn in constitutive CAM species. Instantaneous carbon isotope discrimination showed in vivo carboxylase co‐dominance during the CAM subjective night, initially by Rubisco and latterly C 4 (PEPc), despite both enzymes seemingly activated in vitro. The circadian rhythm in titratable acidity accumulation was progressively damped over successive subjective nights, but maintenance of PEPc carboxylation capacity ensures that CAM plants do not become progressively more ‘C 3 ‐like’ with time under LL.