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Structure - Seeds

Where are the food reserves in seeds?

in cotyledons or endosperm, or both

What are the environmental factors generally required for seed germination?

water and appropriate temperature, sometimes light or other special requirements (cold phase, leaching, scarification)

Which parts of the axis extend and which parts are above ground in epigeous and hypogeous germination?

  • in dicots hypocotyl for epigeous, epicotyl for hypogeous
  • in monocots mesocotyl for hypogeous and cotyledon for epigeous

In what other ways than seeds can plants reproduce or be propagated?

various vegetative methods: stolons, rhizomes, tubers, bulbs, etc.

A cold treatment that prepares seeds for germination is called:

  1. scarification
  2. vernalization
  3. stratification

  1. Scarification involves chemical or mechanical disruption fo the seed coat (which can help germination in certain seeds)

     

  2. Like stratification, vernalization involves cold treatment but it promotes flowering, rather than germination

     

  3. Stratification is often necessary to persuade seeds to germinate.

In a dicot that shows hypogeal germination:

  1. the hypocotyl extends and the cotyledons emerge from the ground
  2. the hypocotyl extends but the cotyledons stay in the ground
  3. the epicotyl extends and the cotyledons stay in the ground

  1. That would be epigeous germination.

     

  2. Since the cotyledons are at the top of the hypocotyl this would present difficulties.

     

  3. Confusingly, in hypogeal germination the epicotyl extends and the cotyledons stay in the ground whereas in epigeal germination the hypocotyl extends and the cotyledons come out of the ground. (It is where the cotyledons end up that defines the terms - hypo for under and epi for above)

Hormones that stimulate seed germination include:

  1. ethylene and gibberellins
  2. cytokinins and auxin
  3. ABA and auxin

  1. Ethylene and, more commonly, gibberellins do promote seed germination.

     

  2. Cytokinins can sometimes promote germination, but this is not a general effect and auxins do not seem to affect germination.

     

  3. ABA naturally accumulates in maturing seeds and inhibits germination; auxins do not seem to affect germination one way or another.

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