Growth and Development of Horticultural Crops (1+1)

Emergence of seedling out of the seed coat

• All the changes described above gradually result in splitting of seed coat and emergence of the growing seedlings.
  
• First the radical comes out and grows downward, then plumule comes out and grows upward. Due to continued growth of this seedling, the plumule comes out of the soil, exposed to light and develops its own photosynthetic organs. Until the seedlings starts producing assimilate by its own photosynthetic organs, the reserve food available in the seed is sufficient to sustain the seedling growth.
  
• Splitting of seed coat may take place either 1) by imbibitional pressure 2) by internal pressure created by the growing primary root 3) by hydrolytic enzymes which act on cell wall contents of seed coat and digest it eg. Cellulase, pectinase etc and sometimes, the seed coat may be extensively damaged by the activity of micro-organisms in the soil.