Seeds

What is often required to break seed dormancy?

environmental changes (temperature or light)

Can seeds remain viable after dormancy?

most seeds remain viable after a year or two of dormancy, some can remain viable for centuries

What is required for seed germination?

water, oxygen, warmth

What is physical dormancy?

the seed coat (testa) is dense and sealed so it is impermeable to water, therefore no imbibition is possible

What is imbibition?

the uptake of water due to the low water potential of the dry seed

What is physical dormancy common in?

forage legumes like alfalfa or red clover

What are methods to break physical dormancy?

chemical digestion, mechanical nicking, freeze thawing

How can chemical digestion break physical dormancy?

chemical digestion occurs in animal digestive tracts.

• acids and enzymes in the stomach soften or scratch the seed coat

• after the seed comes out in poop, it can germinate

How can mechanical nicking break physical dormancy?

humans or nature can scratch or cut the seed coat

How can freeze thawing break physical dormancy?

repeated freezing and thawing cracks the seed coat naturally

What is the first step of seed germination?

imbibition

Why is imbibition a critical step of seed germination?

seeds are very dry, containing only 5-10% of water

What are the cells of dry seeds packed with?

stored proteins, starch, and lipids

What happens after imbibition in seed germination?

enzymes are activated and rapidly released to digest the stored food into smaller molecules which can then be transported and converted into energy needed for growth

What is the first indication that germination has begun?

the swelling of the radicle (embryonic root of the plant) because imbibing water causes the seed to expand and rupture its coat

What happens after seed germination?

cotyledons emerge through the soil and are the first “true leaves” involved in photosynthesis

What is the difference between germination and emergence?

germination is the appearance of the radicle and shoot from the seed. emergence is the appearance of seedling shoot above soil surface