LECTURE 18- seed dormancy and germination

what are the 5 main classes of plant hormones

• Auxin (AUX/IAA)

• Abscisic acid (ABA)

• Gibberellins (GA)

• Cytokinin (CK)

• Ethylene (ETH/C2H4)

what are plant hormones used for

• regulating root, stem, flower, meristem, shoot growth, and germination

• helping the plant respond to the environment

what do gibberellins do during seed germination

cause germination by moving to the aleurone layer and releasing hydrolytic enzymes, sugars and amino acids

• enzymes break down starch + proteins and release sugars + amino acids for seed and coleoptile growth

what does abscisic acid do during seed germination

inhibit seed germination

what makes up a plant embryo

radicle, plumule and cotyledon(s)

what does the seed coat do

protect the plant from harsh conditions

what happens during seed maturation

• sugars, fatty acids and proteins are loaded into the seed, while water is extracted from seed

• dessication occurs in seed: high in food, low in water

• dessication allows seed to survive util favourable conditions

what are the 2 types of seed dormancy

• quiescent seeds

• dormant seeds

what are quiescent seeds

seeds that have stopped developing and are stable and dry. Will quickly germinate when conditions are favourable

what are dormant seeds

seeds that are stable, but need something extra to germinate. They germinate slower than quiescent seeds

what role does abscisic acid play in seed dormancy

regulates seed coat rigidity and ensures the seed coat is impermeable; inhibitor, makes seed dormant

what role do gibberellins play in seed dormancy

are induced by light and can break seed dormancy

• smoke, acid, cold periods, or drought can also activate gibberellins to induce seed germination

how do garden beans germinate

• radicle produces roots

• hypocotyl bends and pushes out of soil to protect meristem and cotyledons from damage

• cotyledons sustain plant

how do castor beans germinate

• hypocotyl pushes out of soil to protect cotyledons + meristem

• cotyledons are leaf-like and can also photosynthesise when plant matures

how do peas germinate

• cotyledons remain in the soil and are purely just an energy source

• epicotyl bends and pushes out of soil

what role does gibberellins play in beer brewing

gibberellins help to cause rapid and uniform germination in barley, to produce consistent and good quality beer