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RHS Year 1 session 8 2011 overview
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RHS Year 1 session 8 2011 overview

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Seed

Seed

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  • 1. RHS Level 2 Certificate Week 8 – Germination, seed dormancy and seed storage.
  • 2. Learning outcomes
    • 1.1 State the environmental requirements for seeds to germinate successfully: light levels; moisture; temperature; oxygen
    • 1.2 Describe the changes that take place in a germinating seed, including taking in water; rising respiration rate; rapid cell division; and the splitting of the seed coat
    • 1.3 State the meaning of the term ‘seed dormancy
    • 1.4 Describe methods of overcoming seed dormancy, including soaking; hot water treatment; nicking (chipping); abrasion; and warm and cold treatments; stating an appropriate plant example for EACH.
    • 1.5 Describe the behaviour of French bean ( Phaseolus vulgaris ), and broad bean ( Vicia faba ) as examples of epigeal and hypogeal germination
    • 1.6 Define the term ‘viability’ in relation to seeds
    • 1.7 State the effect that storage has on the viability and germination potential of seed
  • 3. Parts of the Seed - review
    • Seed – formed from the mature fertilized ovule and containing the embryo and stored food.
    • Parts of the seed – review vocabulary and structure. (Testa, plumule, cotyledons, micropyle, radicle)
  • 4.  
  • 5. Germination
    • Stage one (Imbibition phase) – water enters the seed (imbibition). The seed swells and the testa splits
    • Stage 2 (Lag phase)– respiration begins to speed up, the food in the cotyledons/endosperm is broken down. Called the ‘lag phase’ because nothing obvious is happening.
    • Stage 3 (Emergence phase) – rapid cell division begins, the radicle emerges followed by the plumule and the shoot begins to grow. The process of germination ends when the shoot reaches the surface and begins to photosynthesise.
  • 6. Epigeal Germination
    • The hypocotyl emerges first, the cotyledons are above the soil.
    • The cotyledons photosynthesise.
    • E.g. Phaseaolus vulgaris (French Bean)
  • 7. Hypogeal Germination
    • Cotyledons remain in the soil, plumule emerges first. Cotyledons do not photosynthesise. E.g. Vicia faba (Broad bean) or Pisum sativum (Pea).
  • 8. Key factors for germination
    • Water – needed to begin the process and then for growth
    • Light – presence or absence depends on species
    • Temperature – too cold and the seed may run out of energy before the shoot emerges
    • Oxygen – needed for respiration
    • Food – stored in cotyledons or endosperm
    • Time – depends on the species.
  • 9. Seed dormancy
    • Dormant – a seed which is viable but unable to germinate, either because the external conditions are not correct or because of factors within the seed itself
    • Examples- ‘after ripening’, chemical inhibition, temperature, light (presence or absence), thick seed coat or chemical triggers for germination.
  • 10. Breaking dormancy
    • Scarification – damaging the seed coat by nicking with a knife or rubbing with sandpaper.
    • Soaking – cold or hot water (depends on species) to soften seed coat and remove chemical inhibitors
    • Stratification – controlled exposure to required temperatures for the species (warm or cold). Breaks down inhibitors and/or matures the embryo.
  • 11. Seed Storage
    • Slow rate of respiration within the dormant seed.
    • Viable seed is able to germinate if the right conditions are present.
    • Seed remains viable (alive) for variable periods of time depending on storage conditions and genus/species.
    • Successful storage means controlling the limiting factors of respiration to keep the rate within the seed slow.
  • 12. Learning outcomes
    • 1.1 State the environmental requirements for seeds to germinate successfully: light levels; moisture; temperature; oxygen
    • 1.2 Describe the changes that take place in a germinating seed, including taking in water; rising respiration rate; rapid cell division; and the splitting of the seed coat
    • 1.3 State the meaning of the term ‘seed dormancy
    • 1.4 Describe methods of overcoming seed dormancy, including soaking; hot water treatment; nicking (chipping); abrasion; and warm and cold treatments; stating an appropriate plant example for EACH.
    • 1.5 Describe the behaviour of French bean ( Phaseolus vulgaris ), and broad bean ( Vicia faba ) as examples of epigeal and hypogeal germination
    • 1.6 Define the term ‘viability’ in relation to seeds
    • 1.7 State the effect that storage has on the viability and germination potential of seed