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.

Circadian clock is one of the most fascinating adaptations to life on Earth. Thanks to the internal clock organisms can not only respond to the periodic succession of day and night, but also measure the length of day, which is an indicator of the seasons. Endogenous clock generates rhythms of approximately 24 hours . Setting the clock is done mainly through changes in temperature and light conditions at dawn and dusk.