Plant Growth and Development

SYNOPSIS

• Growth is an increase in the size of an organism or part of an organism, usually as a result of an increase in the number of cells.
• An auxanometer is used to measure the rate of growth in terms of shoot length.
• Phases of Growth
  
  
  
• Growth rate is the number of individuals added per thousand individuals which is represented by a growth curve.
• The population growth curve is of two types—arithmetic growth and geometrical growth [sigmoid growth curve (S-shaped)]
• Totipotency is the ability of a single cell to divide and develop into a new organism.
• A growth regulator or phytohormone is an organic substance produced naturally in plants controlling growth and other functions.
  
  
• Physiological Effects of Plant Growth Regulators
  
  
  

  Hormone	Effect
  Auxins	Promotes the elongation and the growth of stems and roots. Promotes cell division in vascular cambium.
  Gibberellins	Cause stem elongation and leaf expansion but have no effect on roots. Break dormancy of buds and tubers. Used to promote elongation of internodes in sugarcane.
  Cytokinins	Stimulate cell division and prevent the onset of senescence in tissues. Promote the growth of lateral buds. Break dormancy of seeds.
  Hormone	Effect
  Ethylene	Inhibits the growth of lateral buds and causes apical dominance. Breaks the dormancy of buds and seeds.
  Abscisic Acid	Induces and maintains dormancy in many seeds. Inhibits cell division and cell elongation.

• 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.
  
  
  
• Vernalisation is a method of inducing early flowering in plants by pre-treatment of their seeds at low temperature.