Independent circadian regulation of assimilation and stomatal conductance in the ztl-1 mutant of Arabidopsis

We have developed a low-cost, multicuvette infrared gas analyser system for medium-term measurement of gas exchange in Arabidopsis thaliana plants. The system enables parallel measurement of stomatal conductance and CO2 assimilation, providing direct comparison between genotypes. This allows the molecular genetic tools that are available in Arabidopsis to be combined with the power of whole-plant physiology. The system was designed specifically for quantification of circadian rhythms of gas exchange, and controls cuvette relative humidity and CO2 concentration under both continuous light and light-dark cycles. Cuvette humidity is controlled by a unique feedback system that prevents humidity oscillations within the cuvettes. Using this new system we demonstrated that, under continuous light, there was a longer circadian period for both stomatal conductance and CO2 fixation in the zeitlupe (ztl-1) mutant compared to wild type. Wild-type ZTL expression is therefore required for normal cycles of CO2 fixation and stomatal conductance. Furthermore, we demonstrate that different circadian periods can coexist in a single plant, highlighting the cell autonomous nature of the plant circadian oscillator.