Flowering is a complex physiological process which depends on many internal and external factors. Transition from vegetative to generative stage in Arabidopsis thaliana is controlled by several developmental pathways. Among them are: giberellin, autonomous, vernalization, light quality and pho- toperiod pathways. In most of plants flowering depends on light and temperature. Light quality pathway is connected with the shade-avoidance syndrome. Acceleration of flowering during shade-avoidance syn- drome is controlled by three major molecules: phytochrome B, PFT1 protein and FT gene. Interaction of PHYB with PFT1 gene leads to its derepression. Newly synthesized PFT1 protein activates FT gene transcription. Photoperiod pathway includes a.o. photoreceptors (phytochromes, cryptochromes and flavoproteins from ZEITLUPE family), circadian clock’s elements, CO and FT genes. Expression of CO gene, which is thought to act as mediator between biological clock and induction of flowering is regulated by FKF1 protein which belongs to ZEITLUPE proteins family and GIGANTEA protein, which also is circadian clock element. FKF1 is responsible for binding of CDF1 protein to CO gene promotor and repress it’s activity in the morning. High level of FKF1 protein in the afternoon leads to fast CDF1 protein degradation which in turn causes increase of CO mRNA level. To obtain the informations about mechani- sms of CO mRNA and protein levels control will increase the knowledge about regulation of flowering time also in short day plants.