Seed Structure And Seed Germination; Seed Dormancy, Seed Viability, BS Applied biosciences, Semester-1, Plant Physiology

Seed structure:

Seed maturation:

• maturation of seed takes place in the fruit that is on the parent plant.
• Endospermous seed: these are the seeds that have the ability to retain Endospermous tissues. which eventually die but these are surrounded by the layer of living cells, which is called aleurone layer. 
• Non-Endospermous seed: these seeds cannot retain Endospermous tissues. these tissues are absorbed by cotyledons. these than become the food reserves for these seeds.

Dormancy:

• during seed dormancy metabolism falls .
• the number of organelles per cell decrease.
• dehydration occur- its means that content of water also falls.
• vacuole present in the seed deflates.
• in dormancy state food reserves becomes dense crystalline form.

 How seed dormancy is maintained:

• The physical barrier: the physical barrier is the seed coat ( Testa ) which is waxy in nature and water proof and impermeable to oxygen.
• Physical state: it is dehydrated to be stay in dormancy state.
• Chemical inhibitors:  these are also present . its example are alkaloids, mustard oil, organic acid and salts etc.
• in this condition growth promotors are absent.

Seed viability: 

• viability is define as when the  seed are capable of germination when all of the necessary environmental conditions are fulfil  
• the average life span of the seed is about 10 to 15 years.
• some leaves are of very short live like willow seeds  that have life span of about one week. 
• some seeds are very long lived like mimosa seeds that are 221 years. 
• condition are too very important for the long life span.
• these conditions are like dry, cold, anaerobic condition.
• in seed bank these are the main conditions which are maintained.

Germination : the process of breaking of dormancy:

it involves the growth of the embryo and its penetration of the seed coat

Germination stages and events:

Stages that lead to cell division:

The control of food reserves hydrolysis:

• it is controlled by the growth promoters such as the gibberellin hormone and the growth inhibitors such as abscisic acid  
• they perform their function by directly effect the genes that are for enzyme synthesis or the activity of the enzymes themselves. 
• the growth substances are effected by the environmental factors for example light humidity and temperature.
• there is the Negative feedback control of the enzymes:

• the ability of the action of the enzyme is also limited by the substrate.
• when all of the starch in the amyloplast is hydrolyzed the enzyme stop working.
• so that the release of the food that is stored is adjusted to compensate the demand.

The mobilisation of food reserves:  

• the food reserves these are stored in the form of large insoluble macromolecular form.
• for transport they are hydrolyzed  by the enzymes into smaller soluble molecules