Growth and Development of Horticultural Crops (1+1)

Perception of Photoperiodic Stimulus and Presence of a Floral Hormone

• It is now well established that the photoperiodic stimulus is perceived by the leaves. As a result, a floral hormone is produced in the leaves which are then translocated to the apical tip, subsequently causing the initiation of floral primordial.
  That the photoperiodic stimulus is perceived by the leaves can be shown by simple experiments on cocklebur (Xanthium pennsylvanicum), a short day plant. Cocklebur plant will flower if it has previously been kept under short-day conditions. If the plant is defoliated and then kept under short day condition, it will not flower. Flowering will also occur even if all the leaves of the plant except one leaf have been removed.
  
• If a cocklebur plant whether intact or defoliated, is kept under long day conditions it will not flower. But, if even one of its leaves is exposed to short day condition and the rest are under long day photoperiods, flowering will occur.
  
• The photoperiodic stimulus can be transmitted from one branch of the plant to another branch. For example, if in a two branched cocklebur plant one branch is exposed to short day and other to long day photo period, flowering occurs on both the branches. Flowering also occurs if one branch is kept under long day conditions and other branch from which all the leaves except one have been removed is exposed to short day condition. However, if one branch is exposed to long photoperiod and the other has been removed is exposed to short day condition. However, if one branch is exposed to long photoperiod and the other has been defoliated under short day condition, flowering will not occur in any of the branches.