seed structure and germination

Seed Structure and Germination: 

Seed Structure and Germination Internal/External Structure, Metabolic events and Needs for Germination – Why do we have seeds? Presented By:- Arun D. Ugale M.Sc. (Agri.) Genetics And Plant Breeding

Seed Structure: 

Seed Structure Plumule: develops into the stem. Cotelydon: stores or absorbs food for the developing embryo. Radicle: first part of a seedling (a growing plant embryo) to emerge from the seed during the process of germination – primitive root Micropyle: small pore on the seed coat for absorption of water. Testa: outer seed coat, protective layer

Seed Development: 

Seed Development

Conditions for Germination: 

Conditions for Germination 1) Water is needed to: Activate hormones and enzymes Swelling of the seeds = bursting of seed coat. Transport of simple materials to the embryo – to be used for respiration and growth. Metabolic and enzyme actions – occur in solution, therefore need water. Conversion of storage compounds into simple components (i.e. starch to glucose)

Conditions for Germination: 

Conditions for Germination 2) Oxygen is needed for aerobic respiration. Without a supply of oxygen, seeds fail to germinate because of the lack of energy – in the form of ATP.

Conditions for Germination: 

Conditions for Germination 3) Suitable temperature All reactions (in germination) are controlled by enzymes. Optimal temperature for enzyme activity leads to faster rate of germination. Freezing = inactivates enzymes Very high temperatures = denatures enzymes

Metabolic Events of Germination: 

Metabolic Events of Germination 1) Water enters the seed through a hole in the seed coat – microplye. 2) Water moves into the tissues and cells by osmosis. 3) The seed swells and the seed coat bursts. 4) Water activates gibberelline, the hormone needed for breaking the dormancy of the seed.

Metabolic Events of Germination: 

Metabolic Events of Germination 5) Gibberelline activates amylase which catalyzes the break down of starch to maltose to glucose. 6) Glucose is mobilized (transported) to the embryo. 7) Embryo absorbs glucose and uses it for respiration (oxygen needed). 8) Cell division, growth and elongation occurs in the embryo = radicle to root, plumule to stem.

Metabolic Events in Germination: 

Metabolic Events in Germination 9) Nutrients needed for growth all supplied by food stored in cotelydons. 10) As nutrients are consumed, first leaves start to appear = photosynthesis. 11) When photosynthesis starts, seedling absorbs water and minerals from the soil, Co2 from the atmosphere and sunlight.