Processes and Requirements Seed Germination Processes and Requirements

Germination 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 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 Scarification 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 Vigor 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?

Seed Quality What do you do with seeds until they are sold and planted? Store them The goal is to maintain viability and vigor while seeds are in storage What is the best way to store seeds? Cool temperatures 40° is usually good Low humidity About 15%