Posted: November 21st, 2022

PLANT LIFE LAB SEED DORMANCY AND GERMINATION

PLANT LIFE LAB SEED DORMANCY AND GERMINATION
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Seed Dormancy
Plant species differ in the extent to which their seeds become dormant, and in the factors
required to break dormancy in order for germination to begin. Coat-imposed dormancy
requires that the seed coat be broken down in order to allow water to enter, and possibly to
allow inhibitors to leach away. Plant propagators sometimes “scarify” seeds by mechanically
cutting or abrading the seed coat or by treating briefly with strong acid to overcome this type of
dormancy. Embryo, or physiological dormancy is hormonally controlled, and often can only be
broken by specific environmental influences, such as heat, cold, light, dark, etc. Sometimes this
type of dormancy can be artificially broken by treating with gibberellic acid. We will test for
differences in dormancy among different species of wild and domesticated plants.
Materials:
• Seeds. Availability will differ from year to year, and may include:
o Arabidopsis thaliana, Brassicaceae
o Alliaria petiolata, garlic mustard, Brassicaceae
o Phaseolus vulgaris, common bean, Fabaceae
o Gleditsia triacanthos, honey locust, Fabaceae
o Solanum lycopersicum, tomato, Solanaceae
o Solanum dulcamara, bittersweet nightshade, Solanaceae
o Secale cereale, rye, Poaceae
o Setaria sp, foxtail grass, Poaceae
o Daucus carota, cultivated carrot and wild carrot (Queen Anne’s Lace), Apiaceae
o Fagopyrum esculentum, buckwheat, Polygonaceae
o Fallopia japonica, Japanese Knotweed, Polygonaceae
• Paper towels and ziplock plastic bags
• Tape and markers
• P1000s and tips (do not need to be sterile)
• 33% bleach solution, freshly made
• Concentrated sulfuric acid
• Goggles and nitrile gloves
• Small beakers or other containers for soaking and rinsing seeds
• Single-edged razor blades
• Sandpaper
• Fine-tip forceps for placing seeds
• 250 mg/L gibberellic acid (GA3) (approx. 700 uM)
Work in groups. Each group will choose or will be assigned a pair of species in the same
family, one wild and one domesticated. The goal is to investigate whether seed dormancy is
present in your species, and if so, to explore the nature of the dormancy. An additional focus is
to compare seed dormancy in wild vs. domesticated species.
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For each of your two species, you will apply three treatments:
1. A mechanical or chemical treatment for coat-imposed dormancy
2. A combined treatment of mechanical or chemical plus hormone (GA) for
physiological dormancy.
3. You will compare the above to untreated control.
Discuss among your group and with your instructors to select treatments appropriate to your
species.
Procedure
1. Use tape and markers to label 6 plastic bags with the species, treatment, and your group
name and date. The experiment is a 2 x 3 factorial giving 6 conditions:
Control (Untreated)
Mechanical or
Chemical
Scarification
Mechanical or
Chemical
Scarification +
Hormone Treatment
(GA)
Species 1
Species 2
2. For the control and mechanical/chemical treatments, moisten two or more layers of
paper towels with water, then wring out to remove most water. Towels should be
damp, but not dripping wet.
3. For the mechanical/chemical plus hormone treatment, after the towels and sees are in
their plastic bag, moisten the paper towels with a minimum volume of GA solution.
4. Label plastic bags with group name, species name, treatment, 6 in total.
5. Apply your chosen treatments to your seeds. (See below.)
6. Place the treated seeds on top of the paper towel layers.
7. Record the type and precise number of seeds sown in each treatment.
8. Fold in the edges of the paper towels and roll so the seeds can’t fall out and so the roll
will fit in the plastic bags. Place the rolls in the bags. Leave some air space—
germinating seeds require oxygen for respiration.
9. Place your bags in the covered tray provided.
10. The seeds will be kept in a warm area to promote germination.
Treatments
• Mechanical
o Mechanical scarification of medium to large seeds. “Nick” the seed with a singleedged razor blade. Make the nicks shallowly, to avoid damaging the embryo
PLANT LIFE LAB SEED DORMANCY AND GERMINATION
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within. Work carefully, especially with small seeds. Hold these with forceps
when cutting—not your fingers!
o Mechanical scarification for seeds too small to hold onto. Rub and roll seeds
between two pieces of sandpaper until the seed coats are sufficiently abraded.
How do you know when to stop? Your judgment call.
• Chemical
o Bleach (sodium hypochlorite) solution. May oxidize inhibitors (if any) in the seed
coat. Soak seeds in bleach for the planned time, then remove bleach and rinse
seeds several times with tap or deionized water.
o Concentrated sulfuric acid. Chemically weakens the seed coat. May help
overcome coat-imposed dormancy. Exercise extreme caution if you apply this
treatment. Discuss in advance with your instructors how you will carry out the
acid treatment and how you will dispose of the waste. Wear gloves and eye
protection, and work with the acid only in the fume hood.
• Hormone
o Gibberellic Acid (GA). GA may overcome physiological dormancy, but only if it
can enter the seed. First apply the same mechanical or chemical treatment to
the seeds that you used to weaken the seed coats in the other treatment. Then
roll/fold the seeds into paper towels, place in their plastic bag and moisten the
paper with the provided GA solution. Be sparing, adding a mL at a time and
waiting for the solution to soak in. You want enough liquid so seeds can imbibe,
but you don’t want it to be soggy.
We will follow up in coming weeks.
• Check your experiments each week.
• Remove any germinated seed and record the number and date. Discard the germinated
seeds, then re-roll the paper towels and reseal in the plastic bags.
• At the end, count and record ungerminated seed.
• Graph % seed germination over time for each species and treatment.
Did your experiments reveal anything about the type and extent of dormancy in the species
tested? Do the dormancies you observed seem adaptive, given what you know about the
biology of the species? Did you find differences in seed dormancy between wild and
domesticated genotypes? Comment on why this would or would not be expected.

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