The Influence Of The Circadian Clock On Stomal Conductance And Carbon Assimilation In Arabidopsis thaliana

Plants have evolved an internal feedback system of gene expression, the circadian clock, to allow for adaptations to changes in diurnal conditions to maximise their ability to utilise the environment for nutrients and growth. The circadian clock aligns the plants processes with fixed external signals, such as the light intensities at dawn and dusk. This study investigated the influence of the circadian clock on stomatal conductance and carbon assimilation and the decoupling of these processes. Timing of Cab (TOC1) and Circadian Clock Associated 1 (CCA1) genes were overexpressed and tested to investigate the impact of altered clock rhythms. Evidence showed of significant increases in carbon assimilation for the TOC1 overexpressed genotype compared to the CCA1 overexpressed genotypes. Data also showed the TOC1 overexpressed genotype had a lower Water Use Efficiency (WUE) than any of the other genotypes, signifying a potential weakening of stomatal sensitivity to internal water levels and allowing for increased photosynthesis at the detriment of water conservation. Changes to light conditions were investigated to look at any corresponding impact on the decoupling of processes when the plant would not be able to correctly align itself to dawn. Changes in light regimes were shown to increase the extent of the decoupling between stomatal conductance with carbon assimilation. Shifting the timings of dawn 2 hours behind “natural dawn” were shown to impact the size but not the timing of the decoupling in relation to the initial increase in light intensity. Overall, this study suggests that the circadian clock is not the cause of the decoupling between these processes but does have an impact on the size of the difference between these process that were thought closely linked.