seed germination

Seed Germination

Processes and Requirements

• What is germination?– I have used this word before in class

• It is when the first embryonic root emerges from the seed coat

• Germination is a process that begins only when certain conditions are met

Germination

Germination• Seeds from some plants will

germinate as soon as they are released

• Others go dormant (a type of hibernation)

– They remain dormant until proper conditions are met

– What do you think some of those conditions are?

Types of Dormancy• Stratification– Triggered by temperature– Must go through a period of cold– And then warm up

• Scarification– Triggered by break-down of the seed coat– What are some ways that a hard seed

coat could be broken down?

Stages of Germination• # 1 – Imbibition– Absorption of water

• Usually dormant seeds have 5-10% moisture content

• At proper conditions water is imbibed very quickly

• What does this do to the seed?– It swells– Becomes turgid

Stages of Germination• # 2 – metabolic activity surges– Proteins are made– Enzymes are produced• Amylase – converts starch to sugar• Protease – breaks down stored proteins into

amino acids– Sugars and amino acids are sent to

meristems• That is where growth takes place• Tips of the root and shoot

Stages of Germination• #3 – metabolic processes increase– Swelling cells break seed coat– Root tip emerges downward– Stem shoot grows upward– Shoot begins photosynthesis– Root begins absorbing water and

nutrients

Conditions for Germination• Conditions have to be right for the

new plant to survive• They include:– Water– Air– Temperatures– Light/Darkness

Conditions for Germination• Water triggers the process– How much moisture is usually in the

seed?• Oxygen must be present for the seed

to germinate– It is needed for cellular respiration• Converts stored food into energy

Conditions for Germination• Temperature– Some seeds can begin germinating at as

low as 32°F or as high as 105°F– Optimum Temperature is usually

between 65°F and 80°F• Temperature influences metabolic

activity– Usually faster at higher temps and slower

at lower temps

Conditions for Germination• To begin germination:– Some seeds actually need light– Others need darkness

• Light sensitive seeds have a photoreceptor pigment in their seed coat– Called Phytochrome– It sends a message to the seed to begin or

stop germination

Seed Quality• Is seed quality important?– Why

• If you buy a bag of seeds to plant, how many do you want to grow?

• Good seeds make good plants

Seed Quality• Defined by two things:– Viability• Ability of seeds to germinate under optimal

conditions– Vigor• Ability of seeds to germinate under different

conditions and still produce healthy plants

Seed Quality• Seed producers test seeds for

germination rates

• These rates are printed on the label of the seeds you buy

• How do they perform the test?