The rotation of earth around its axis leads to environmental changes in light intensity and temperature that predictably define day-night cycle. Most organisms coordinate their life cycle in anticipation of these environmental fluctuations. The measurement of time and synchronization with the environment are achieved by an internal time-keeping mechanism biological clock. The circadian clock is an endogenous mechanism that generates rhythms with an approximately 24-h period and enables plants to adapt to daily and seasonal changes in their environment.

Brassinosteroids (BR) are hormones displaying high activity in stimulation of plant growth and development. They are present at low concentrations in pollen grains, anthers, seeds, leaves, stems, roots and vegetative tissues undergoing early developmental stages in a broad range of species representing various evolutionary groups. The richest sources of brassinosteroids are pollen grains and immature seeds, whereas leaves and stems contain much lower concentration of these hormones.