Modulation of clock dynamics by ABA. Diurnal profiles of TOC1 mRNA (A) under various levels of ABA (ABA level is expressed in relative units; the wild-type level is 1). Simulations were run under a 12 L:12D diel cycle. B: Free running oscillation of LHY/CCA1 and TOC1 mRNA under constant light conditions in the absence or presence of ABA. The 1.3 h period lengthening in the presence of increased ABA in the model simulation is close to the reported 1.5 h lengthening of the period of the clock marker CAB2: LUC under constant light conditions .