Week 14 L5: Plant Development 3 - Embryo Development

Question 1

Do plants have an axis when they germinate?

Answer 1

YES, have a sense of polarity

Question 2

Are meristems formed early in development of the embryo?

Answer 2

yes, it can be seen between globular and heart that meristems are becoming visible

Question 3

What forms of the meristem show polarity in the embryo?

Answer 3

SAM and root meristem

Question 4

What are the stages of embryogenesis?

Answer 4

globular , heart , torpedo , mature.

Question 5

What is the relationship between embryo and endosperm development?

Answer 5

develop in tandem

Question 6

What is the endosperm like when the seed is mature?

Answer 6

very little endosperm left, seed been taken up by the embryo.

Question 7

What is a transient endosperm?

Answer 7

endosperm has virtually disappeared by germination. When the seed is mature there is very little endosperm left

Question 8

What are the different types of endosperm?

Answer 8

transitive and persistent

Question 9

What is germination?

Answer 9

the development of a plant from a seed or spore after a period of dormancy.

Question 10

What plants have transitive endosperm?

Answer 10

arabidopsis

Question 11

What type of plant have persistent endosperm?

Answer 11

barley grain (and other cereal grains)

Question 12

What does a persistent endosperm mean?

Answer 12

it supports the germinating seedling

Question 13

Why would cereals want a persistent endosperm?

Answer 13

It has a large source of calories.

Question 14

In sweetcorn what is the largest source of calories in the endosperm?

Answer 14

starch

Question 15

What is it about grains which make them a good food source?

Answer 15

double fertilisation and persistent endosperm.

Question 16

What is syncytial development?

Answer 16

nuclei in the endosperm are just dividing. increase number of nuclei very quickly.
development of early endosperm

Question 17

What happens in double fertilisation?

Answer 17

process of double fertilization occurs, since one of the nuclei of the pollen grain fuses with the two polar nuclei of the embryo sac to form a cell with three nuclei and the other fuses with the nucleus of the ovum.

Question 18

What are the stages of endosperm development in embryogenesis?

Answer 18

free nuclear development
cellularization
cellular growth

Question 19

What are the filial tissues?

Answer 19

endosperm and embryo

are apoplasmically separated from the maternal tissue

Question 20

What maternal tissue delivers nutrients to the developing endosperm and embryo?

Answer 20

nucellar projection

and nucellar epidermis

Question 21

What receives the nutrients from the nucellar projection?

Answer 21

modified aleurone (also called transfer cells)

Question 22

What 2 structures are important to deliver nutrients into the embryo?

Answer 22

nucellar projection

modified aleurone

Question 23

What works coincidently with maternal tissue degradation?

Answer 23

grain filling

Question 24

What happens 10 days after pollination?

Answer 24

cavity and programmed cell death of the nucellar projection

Question 25

What promotes maternal tissue degradation?

Answer 25

B-sister genes

Question 26

What are the B-sister genes?

Answer 26

closely related to B-class MADS-box

Question 27

What happens if the maternal tissue does not degrade?

Answer 27

no endosperm development

Question 28

What is dormancy?

Answer 28

Generally an adaptive trait ensuring that germination occurs in a suitable environment at a suitable time

Question 29

What is a dormant seed?

Answer 29

doesn’t germinate under normal | growth conditions.

Question 30

Why have dormancy?

Answer 30

The conditions may be optimal for an adult but not for a seedling. seedlings need more water than adults. Seedlings are laying down cuticle, don't have mature cuticle. sensitive part of their life. Not a lot of leaves etc. Allows plant to wait of the optimal environment to germinate. • Water –seedlings much more sensitive to drought than adult plants. • Time for dispersal • Light • Sufficient to generate enough photosynthate to survive. • Avoid germination in shady places, e.g; canopy cover

Question 31

What is photosynthate?

Answer 31

a sugar or other substance made by photosynthesis.

Question 32

Why don't we want a seed to prematurely germinate?

Answer 32

as the seed will use all the starch in the endosperm Defective barley. e.g. premature spouting of corm

Question 33

What factors can cause dormancy to break?

Answer 33

physical chemical physiological

Question 34

What are the physical aspects leading to dormancy to break?

Answer 34

Needs breaking to germinate (freezing, high temp, digestive tract, drying) as otherwise water can’t get in. • Can be one cycle or multiple lasting months to years.

Question 35

What are chemical aspects leading to dormancy to break?

Answer 35

Inhibitors present in the seed coat – need to be | washed out before germination can occur.

Question 36

What are the physiological aspects leading to dormancy breaking?

Answer 36

Hormone antagonism | • Abscisic acid (ABA) vs Giberellins (GA)

Question 37

What hormone promotes dormancy?

Answer 37

aba

Question 38

When will a mature seed undergo a secondary dormancy?

Answer 38

Potentially if hydration occurs and a physical barrier is overcome. But this isn't enough to germinate so a secondary dormancy occurs. GA levels rise slightly but are overridden by ABA levels increasing. insurance policy, seed is wet but unsure, needs more barriers overcome.

Question 39

What is a seedling called when it undergoes a second dormancy?

Answer 39

Imbided

Question 40

What is an imbided seed?

Answer 40

e.g. hydration and physical barrier overcome. Seed swells, increase GA levels but ABA shoot up.

Question 41

What is a breaking dormancy signal?

Answer 41

many siganls | light, hydration, cold, chemical suppression lost etc.

Question 42

What happens when the seedling breaks the dormancy signals? GA/ABA

Answer 42

GA increases and aba DECREASES. But also the sensitivity to ABA decreases and the sensitivity to GA increases The seedling is committed to germination. GA is produced by the seed after imbibition but the seed isn’t sensitive to GA. • Light (and cold or other stimuli) promote increased production of GA and increased sensitivity to GA by repressing ABA synthesis and promoting ABA catabolism. • Eventually GA production causes inhibition of ABA synthesis and promotes degradation of ABA by upregulating ABA catabolism genes.

Question 43

What is hormonal antagonism?

Answer 43

influencing the levels and sensitivity of each there ABA/GA

Question 44

What is an example of a cereal that has been bred to have reduced dormancy?

Answer 44

wheat

Question 45

What is an advantage to crops having reduced dormancy?

Answer 45

Immediate synchronous germination straight after planting

Question 46

What is a disadvantage of crops having reduced dormancy?

Answer 46

• Rain fall on ripe crops can induce pre-harvest germination • Germination in storage. wet conditions can cause it to pregerminate

Question 47

What kind of germination is wanted in malt?

Answer 47

Vigorous and synchronous germination important for malting, release sugars for fermentation. GA induces production of an enzyme amylase. amylase breaks starch to sugar. This sugar is what the yeast will go on and ferment and give alcohol.

Question 48

When do malters want to have vigorous germination of malt?

Answer 48

sugar release stage | They want enough sugar release but want to kill that seed so it doesn't use the sugar and grow.