Crassulacean Acid Metabolism (CAM) is found in approximately 7% of plant species, and may be thought of as an adaptation to maximise water use efficiency in arid environments. CAM plants open their Stomata at night, using the enzyme Phosphoenolpyruvate carboxylase (PEPc) to fix CO2 into organic acids. During the next day these acids are decarboxylated behind closed stomata, and the released CO2 is subsequently refixed by a second carboxylase, Rubisco. The circadian and metabolic factors controlling PEPc activity are well known. However, only recently have studies begun to elucidate the factors modulating Rubisco activity during CAM. In contrast to C3 plants, Rubisco in CAM plants is regulated independent of light intensity and internal CO2 concentration, with maximum activity observed late in the photoperiod.
In my PhD I am investigating the key factors controlling Rubisco activity in C3 and CAM forms of the South African annual halophyte Mesembryanthemum crystallinum (L.). M. crystallinum induces CAM developmentally, though induction may be rapidly accelerated by abiotic stress. I have looked at the co-regulation of the two carboxylases, Rubisco and PEPc, over both the diel cycle and during the ten days of the C3 to CAM transition. Further work includes monitoring C3 and CAM M. crystallinum under 24hr constant illumination. Using a range of Physiological, Biochemical and Molecular tools, I hope to determine the circadian processes regulating Rubisco activity in CAM plants.
Nimmo, HG (2000) The regulation of Phosphoenolpyruvate carboxylase in CAM plants. TRENDS IN PLANT SCIENCE 5 (2) pp. 75-80
Griffiths, H et al (2002) Regulation of Rubisco activity in CAM plants: better late than never. FUNCTIONAL PLANT BIOLOGY 29 (6) pp. 689-696
Maxwell, K et al (1999) Modulation of Rubisco activity during the diurnal phases of the Crassulacean acid metabolism plant Kalanchoe daigremontiana. PLANT PHYSIOLOGY 121 (3) pp. 849-856