Seeds and Germination Flashcards
What is a seed?
The result of sexual reproduction,
A new generation with characteristics of both parents,
A survival mechanism.
Name 8 components of seed structure.
Testa, Hilum, Plumule, Epicotyl, Hypocotyl, Embryo, Radicle, Cotyledon.
What is a testa?
The covering layer of the seed.
What is a cotyledon?
Fleshy lobes that act as a starch/ nutrient store for germination.
What is an embryo?
The embryo contains genetic information from both parents.
What is a plumule?
The embryonic shoot.
What is a radicle?
The embryonic root.
What is the epicotyl?
The shoot from which the entire plant shoot system developed. The growing tip of the epicotyl is the plumule.
What is the hypocotyl?
The zone between the rudimentary root and shoot.
Define dormancy.
A state of metabolic arrest that facilitates the survival of organisms during environmental conditions that are incompatible with their regular course of life.
or
Temporary failure of a viable seed to germinate in conditions that favour germination.
Describe enforced dormancy.
Dormancy is forced upon the seed by some limitation of the germination environment.
Describe innate dormancy.
Dormancy is imposed upon the seed by the mother plant. The seed remains dormant for some time after the seed is shed, even under perfect conditions.
Describe induced/ secondary dormancy.
Acquired condition of the inability to germinate caused by some experience after ripening.
State 3 ways pyroendemics break dormancy.
Fracturing or desiccation of the seedcoat by heat.
Heat signals may directly stimulate the embryo.
Chemicals from combustion induce germination.
Name 3 seed treatments.
Seed priming,
Seed coating,
Seed conditioning.
Describe germination (4 points).
The transition from embryonic to post-embryonic growth.
Starts with imbibing the seed in water, causing swelling and an increase in size.
Cells elongate and being to divide and differentiate.
Leaves begin to photosynthesise and the new plant becomes independent of energy stored in the seed.
How do gibberellin and abscisic acid affect germination?
Gibberellin stimulates, ABA represses.
State 3 points related to temperature and germination.
Seeds continuously deteriorate and will die unless they germinate.
Most seeds are initially dormant, relatively dry seeds continuously lose dormancy at a rate that is temperature dependent.
Once seeds lose dormancy the rate of germination increases linearly between the base and optimum temps. and declines linearly between optimum and ceiling temps.
Describe light-mediated seed germination.
It is a mechanism for avoiding germination in the shade of other plants. Generally favoured by sun-loving seed plants like Arabidopsis, that lack the energy reserves to emerge and then elongate out from beneath the shade of other plants.
Describe light-dependent seed germination.
Seed germination is suppressed in the dark and stimulated in sunlight.
An adult leaf will filter out the red light required for germination, but not far-red light which inhibits germination.
When no adult canopy is present, red light stimulates germination.
What kind of seeds tend to be able to germinate in the dark?
Large seeds.
Describe a recalcitrant seed.
Short-lived seeds that can not be dried to below 20-30% moisture content without injury, and won’t tolerate freezing.
Describe an orthodox seed.
A long-lived seed that can be frozen and dried to 5% moisture content.
What is vigour in seed terms?
A measure of quality.
