Coordination in Plants

Synopsis

Control and Coordination 

• Control is the power of restraining and regulation by which something can be started, slowed down or stopped. 
• Co-ordination is the working together of various agents of the body of an organism in a proper manner to produce an appropriate reaction to a stimulus.
• The mechanism of maintaining internal steady state is called homeostasis.
  
  

Movements in Plants

 

Nastic Movements

• The movement of a plant in response to an external stimulus, in which the direction of response is not determined by the direction of stimulus, is called nastic movement.
• Nastic movements are shown by flat parts of the plants such as leaves and petals.
• Two types of nastic movements are:

1. Photonasty is a nastic movement to the light and dark phases of the day.
   Example- Flowers of primrose blossom during the evening but close during the day.
2. Nyctinasty is the movement in response to dark. Certain parts of a plant such as the leaves and flowers take up a different posture at night than that in the day. Example- Leaves of the rain tree fold by nightfall.
   
   

 

Tropic Movements

• The movement of plant organs towards or away from a stimulus is known as tropism. 
• Since the tropic movements are slow, the stimulus needs to be continued for a longer time for the effects to be noticed. 
• The different types of tropic movements in plants are:
  
  

 

Photoperiodism 

• The response of plants to the relative lengths and alternations of light and dark periods with respect to the initiation of flowering is called photoperiodism.
• On the basis of photoperiodic response to flowering, plants have been divided into the following categories:
  
  

Vernalisation 

• Many plants such as cereals, crucifers and roses require a period of cold treatment before flowering.
• Vernalisation is a method of inducing early flowering in plants by pretreatment of their seeds at low temperature.
• This condition occurs in winter varieties of some annual food plants (wheat, barley), some biennial plants (cabbage, carrot) and perennial plants (Chrysanthemum).
• The site for vernalisation is the meristematic cells such as shoot tips, embryo tips, root apices and developing leaves.

 

Importance of Vernalisation

• It can help in shortening the juvenile or vegetative period of plants to bring early flowering. Examples: Wheat, rice, millets
• It increases yield and resistance to cold and diseases.
• Kernel wrinkles of Triticale, a hybrid of wheat and rye, can be removed by vernalisation.

 

Plant Hormones (Phytohormones)

Plant hormones control some aspects of the growth of plants such as cell division, cell enlargement and cell differentiation.