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

Summary•  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 CO 2 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 CO 2 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 CO 2 fixation in the zeitlupe ( ztl‐1 ) mutant compared to wild type. •  Wild‐type ZTL expression is therefore required for normal cycles of CO 2 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.