JXB Advance Access published online on March 31, 2003
Journal of Experimental Botany, doi:10.1093/jxb/erg152
© 2003 by Oxford University Press
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1 Adam Mickiewicz University, Biology Department, Al. Niepodleg
* To whom correspondence should be addressed. E-mail: twyka{at}amu.edu.pl.
During the endogenous circadian rhythm of carbon dioxide uptake in continuous light by a Crassula cean acid metabolism plant, Kalanchoë daigremontiana, the two carboxylating enzymes, phosphoenolpyruvate carboxylase (PEPC) and ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco), are active simultaneously, although, until now, only the role of PEPC in generating the rhythm has been acknowledged. According to the established model, the rhythm is primarily regulated at the PEPC activity level, modulated by periodic compartmentation of its inhibitor, malate, in the vacuole and controlled by tension/relaxation of the tonoplast. However, the circadian accumulation of malic acid (the main indicator of PEPC activity) dampened significantly within the first few periods without affecting the rhythm's amplitude. Moreover, the amount of malate accumulated during a free-running oscillation was several-fold lower than the amount expected if PEPC were the key carboxylating enzyme, based on a 1:1 stoichiometry of CO2 and malate. Together with the observation that rates of CO2 uptake under continuous light were higher than in darkness, the evidence shows that C3 carboxylation greatly contributes to the generation of rhythmic CO2 uptake in continuous light in this ‘obligate' CAM plant. Because the shift from predominantly CAM to predominantly C3 carboxylation is smooth and does not distort the trajectory of the rhythm, its control probably arises from a robust network of oscillators, perhaps also involving stomata.
© 2003 Society for Experimental Biology
RESEARCH PAPER
Contribution of C3 carboxylation to the circadian rhythm of carbon dioxide uptake in a Crassulacean acid metabolism plant Kalanchoë daigremontiana
o
ci 14, 61-714 Pozna
, Poland
2 Technische Universität-Darmstadt, Institut für Botanik, Fachbereich Biologie, Schnittspahnstr. 3-5, D-64287 Darmstadt, Germany
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