JXB Advance Access published online on December 15, 2005
Journal of Experimental Botany, doi:10.1093/jxb/erj028
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1 School of Biology, Institute for Research on the Environment and Sustainability, Devonshire Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK
* To whom correspondence should be addressed. In the halophytic species Mesembryanthemum crystallinum, crassulacean acid metabolism (CAM) may be induced by a range of abiotic factors including drought, salinity, high light intensity, low temperature, and anoxia. A key biotic consequence of all these environmental changes is the generation of reactive oxygen species in planta that can elicit potentially damaging oxidative reactions and/or act as signals for engaging mechanisms that alleviate oxidative stress. However, induction of CAM per se also has the potential for increasing the oxidative burden via the enhanced internal O2 concentrations that develop behind closed stomata during daytime decarboxylation. The aim of this paper was to test two hypotheses. The first one, that reactive oxygen species are key signals for up-regulating the major genes and proteins required for the operation of CAM as part of an integrated strategy for alleviating oxidative burden, was tested using gaseous ozone to increase the oxidative burden at a cellular level. The second hypothesis, that CAM potentially increases oxidative load, was tested using a CAM-deficient mutant of M. crystallinum. The data indicate that ozone, like salinity, elicits an increase in the transcript and protein abundance of myo-inositol o-methyl transferase (a key enzyme of cyclitol synthesis), together with phosphoenolpyruvate carboxylase and other ‘CAM-related’ enzymes. However, ozone, unlike salinity, does not induce functional CAM, implying that the various metabolic components required for CAM respond to different signals. Comparing the activities of different subcellular isoforms of superoxide dismutase in wild-type and CAM-deficient mutants of M. crystallinum suggests that the induction of CAM potentially curtails the oxidative load in planta.
Received May 5, 2005
Accepted October 24, 2005
PHENOTYPIC PLASTICITY AND THE CHANGING ENVIRONMENT SPECIAL ISSUE ARTICLE
Are the metabolic components of crassulacean acid metabolism up-regulated in response to an increase in oxidative burden?
Anne Borland 1 *,
Stewart Elliott 1,
Susan Patterson 1,
Tahar Taybi 1,
John Cushman 2,
Beata Pater 3,
and
Jeremy Barnes 1
2 Department of Biochemistry, University of Nevada, Reno, NV 89557-0014, USA
3 Institute of Plant Physiology, Polish Academy of Sciences, 31-016, Krakow, Poland
Anne Borland, E-mail: a.m.borland{at}ncl.ac.uk
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