Seeds

Question 1

What are the 3 stages in grain filling?

Answer 1

1. Embryogenesis
2. Maturation
3. Drying to 10% moisture content

Question 2

What is imbibition?

Answer 2

Rehydration

Question 3

What is seed maturation controlled by?

Answer 3

ABA, sucrose and chromatin remodelling

Question 4

Which seed type can be dried down?

Answer 4

Orthodox

Question 5

What provides orthodox seeds with protection from desiccation damage?

Answer 5

1. Synthesis of stress related sugars and proteins (heat shock proteins and LEA proteins)
2. Protection of membranes and macromolecules
3. Interactions between sugar and protein complexes stabilise their physical structure (sugars replace water).

Question 6

How many storage reserve types will any one seed have?

Answer 6

2

Question 7

What is the storage organ in non-endosperms?

Answer 7

Cotyledons, in plants with endosperms, it is this that is used in nutrient uptake

Question 8

What are cotyledons?

Answer 8

Embryonic seed leaves

Question 9

What is the hypocotyl?

Answer 9

Stem-like embryonic axis

Question 10

What is the radicle?

Answer 10

The embryonic root

Question 11

How does the seed take up nutrients since it has no direct vascular connection to the mother plant?

Answer 11

From the phloem into the maternal tissues by active transport into the apoplast and endosperm cavity.

Question 12

Where is starch deposited?

Answer 12

In modified plastids called amyloplasts.

Question 13

Give 4 storage proteins

Answer 13

1. Albumins
2. Globulins
3. Prolamins
4. Glutenins

Question 14

What transports amino acids across the plasma membrane?

Answer 14

Amino acid permeases

Question 15

What are the roles of APP1 and APP2?

Answer 15

APP1 - taking up amino acids into the endosperm

APP2 - Unleading amino acids from the maternal tissues into the apoplast

Question 16

What happens in the 3 phases of germination?

Answer 16

1 - rapid increase in water content driven by osmosis, DNA repair
2 - Prepare for germination or desiccate again
3. Water uptake increases due to growth of new tissues

Question 17

Give 3 environmental cues

Answer 17

1. temp
2. Light and light quality
3. Chemicals such as nitrate and smoke

Question 18

Give 2 intrinsic capabilities

Answer 18

1. Capacity to germinate? Viable

2. Weakening of seed coat

Question 19

What is the difference between dormancy and quiescence?

Answer 19

Dormancy: intrinsic property of a seed, will not germinate if internal signalling is telling it not to
Quiescence: low metabolic activity, germination isn’t possible due to low metabolic activity

Question 20

What is the gene which causes pre-harvest sprouting in maize?

Answer 20

Viviparious-1 (VP1)

Question 21

What does VP1 control?

Answer 21

ABA signalling pathway

Question 22

What does ABA do?

Answer 22

Inhibits germination and induces dormancy

Question 23

What happens in plants with the abi mutant?

Answer 23

ABA insensitivity so show reduced dormancy, can germinate in the presence of ABA

Question 24

What is Abi1?

Answer 24

A type 2C protein phosphatase which dephosphotylates a SNF-1 SnRK2 protein kinase so it cannot bind to the transcription factors and so ABA signalling is not possible

Question 25

What should happen in a WT plant in ABA signalling?

Answer 25

In the presence of ABA the receptor binds PP2C so it cannot dephosphorylate SnRK2 allowing signalling of ABA and preventing germination

Question 26

Which hormone stimulates germination?

Answer 26

Gibberellin

Question 27

What causes the formation of Pr?

Answer 27

Absorbance of red light (660nm) from previous exposure to far red light - represses dormancy

Question 28

What causes formation of Pf?

Answer 28

Absorbance of far red light (<660nm) from previous exposure to red light - breaks dormancy

Question 29

What does far red light do to levels of gibberellin?

Answer 29

Decreases the pool of active gibberelling so ABA can keep the seeds dormant

Question 30

What does red light do to the levels of gibberellin?

Answer 30

Increases the pool of active gibberellin by increasing transcription of GA3ox allowing active gibberellin (GA4) which decreases ABA synthesis

Question 31

Which gene controls the levels of gibberellin and ABA in seeds?

Answer 31

Delay of germination (DOG-1). Active DOG-1 increases the levels of dormancy.

Question 32

What releases a large amount of hydrolytic enzymes in reserve mobilisation?

Answer 32

Aleurone layer

Question 33

What is the scutellum?

Answer 33

Important in the mobilisation of reserves - good transport capacity

Question 34

How is insoluble starch converted to glucose?

Answer 34

Combined action of a-amylase, B-amylase, limit dextrinase and a-glucosidase

Question 35

What is PSV?

Answer 35

Protein storage vacuole

Question 36

When proteins have been broken down, where are they transported to?

Answer 36

From the endosperm to the embryo

Question 37

How are nucleic acids broken down?

Answer 37

NucleaseI forms mononucleotides and then acid phosphatases form mononucleosides (phosphate group)

Question 38

What seeds does the viability equation apply to?

Answer 38

Orthodox only as they respond in a quantifiable and predictable way

Question 39

What is Osmopriming?

Answer 39

Restriction of the amount of water that the seed can take up so germination cannot occur although pre-germination processes like DNA repair can

Question 40

What is hydropriming?

Answer 40

Continuous or successive addition of a limited amount of water to the seeds.