1. Vegetative Plant Development
Chapter 37

2. Embryo Development Begins once the egg cell is fertilized
-The growing pollen tube enters angiosperm embryo sac and releases two sperm cells
-One sperm fertilizes central cell and initiates endosperm development
-Other sperm fertilizes the egg to produce a zygote
-Cell division soon follows, creating the embryo

3. Polar nuclei Egg cell just before fertilization Integuments
(ovule wall)
Micropyle
Pollen tube
Sperm cell
fertilizing
central cell
egg cell
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4. Embryo Development
The first zygote division is asymmetrical, resulting in two unequal daughter cells
-Small cell divides repeatedly forming a ball of cells, which will form the embryo
-Large cell divides repeatedly forming an elongated structure called a suspensor
-Transports nutrients to embryo
The root-shoot axis also forms at this time

5. Embryo Development Polar nuclei Egg Micropyle Sperm Pollen tube
3n endosperm
2n zygote

6. Embryo Development First cell division Endosperm Suspensor Basal cell
Cotyledon
Procambium
Ground
meristem
Protoderm
Root apex
(radicle)
Globular
proembryo
Hypocotyl
Root apical
Cotyledons
Shoot
apical
Shoot apical meristem

7. Embryo Development
Asymmetrical cell division is also observed in the zygote of the brown alga Fucus
-Unequal material distribution forms a bulge
-Cell division occurs there, resulting in:
-A smaller cell that develops into a rhizoid that anchors the alga
-A larger cell that develops into the thallus, or main algal body
Fate of two cells is held “in memory” by cell wall components

8. Embryo Development Zygote Young alga Adult alga Light Bulge Rhizoid
Rhizoid cell
Thallus
Thallus cell
Young alga
Adult alga
First cell
division
(asymmetrical)
Gravity

9. Embryo Development
Arabidopsis mutants have revealed the normal developmental mechanisms
-Suspensor mutants undergo aberrant development in the embryo followed by embryo-like development of the suspensor
-Thus, the embryo normally prevents embryo development in suspensor

11. Development of Body Plan
In plants, three-dimensional shape and form arise by regulating cell divisions
-The vertical axis (root-shoot axis) becomes established at a very early stage
-Cells soon begin dividing in different directions producing a solid ball of cells
-Apical meristems establish the root-shoot axis in the globular stage

12. Development of Body Plan
The radial axis (inner-outer axis) is created when cells alternate between synchronous cell divisions
-Produce cells walls parallel to and perpendicular to the embryo’s surface
The 3 basic tissue systems arise at this stage
-Dermal, ground and vascular

13. Cell wall forming parallel
Development of Body Plan
Embryo
Suspensor
Root–shoot axis
Radial axis
Cell wall forming parallel
to embryo surface

14. divisions, accompanied by apical growth divisions
Development of Body Plan
Cell wall
forming
perpendicular
to embryo
surface
Multiple parallel
and perpendicular
divisions, accompanied
by apical growth divisions
lengthening the root–
shoot axis
Vascular tissue system
(procambium)
Ground tissue system
(ground meristem)
Dermal tissue system
(protoderm)
Shoot apical meristem
Root apical meristem
Root–shoot
axis

15. Development of Body Plan
Both shoot and root meristems are apical meristems, but are independently controlled
-Shootmeristemless (STM) is necessary for shoot formation, but not root development
STM wild type
stm mutant
-STM encodes a transcription factor with homeobox region

16. Development of Body Plan
The HOBBIT gene is required for root meristem, but not shoot meristem formation

17. Development of Body Plan
One way that auxin induces gene expression is by activating the MONOPTEROS (MP) protein
-Auxin releases the repressor from MP
-MP then activates the transcription of a root development gene

19. Development of Body Plan

20. Formation of Tissue Systems
Primary meristems differentiate while the plant embryo is still at the globular stage
-No cell movements are involved
The outer protoderm develops into dermal tissue that protects the plant
The ground meristem develops into ground tissue that stores food and water
The inner procambium develops into vascular tissue that transports water & nutrients

22. Morphogenesis
The heart-shaped globular stage gives rise to bulges called cotyledons
-Two in eudicots and one in monocots
These bulges are produced by embryonic cells, and not by the shoot apical meristem
-This process is called morphogenesis
-Results from changes in planes and rates of cell division

23. Morphogenesis
The form of a plant body is largely determined by the plane in which its cells divide
-Based on the position of the cell plate
-Determined by microtubule orientation
Microtubules also guide cellulose deposition as the cell wall forms around the new cell
-Cells expand in the directions of the two sides with the least cellulose reinforcement

24. a. b. Nucleus Microtubules Cell division Forming cell plate Cellulose
fiber
Water uptake
Expansion a. b.
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25. Morphogenesis
Early in embryonic development, most cells can give rise to a wide range of cell and organ types, including leaves
-As development proceeds, the cells with multiple potentials are restricted to the meristem regions
-Many meristems have been established by the time embryogenesis ends and the seed becomes dormant

26. Morphogenesis
During embryogenesis, angiosperms undergo three other critical events:
-Storage of food in the cotyledons or endosperm
-Differentiation of ovule tissue to form a seed coat
-Development of carpel wall into a fruit

27. Morphogenesis Endosperm varies between plants
-In coconuts it is liquid
-In corn it is solid
-In peas and beans it is used up during embryogenesis
-Nutrients are stored in thick, fleshy cotyledons

29. Seeds
In many angiosperms, development of the embryo is arrested soon after meristems and cotyledons differentiate
-The integuments develop into a relatively impermeable seed coat
-Encloses the seed with its dormant embryo and stored food

30. Shoot apical meristem Seed coat (integuments) Procambium Root apical
Cotyledons
Root cap
Root apical
meristem
Procambium
Endosperm
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31. Seeds Seeds are an important adaptation because:
1. They maintain dormancy under unfavorable conditions
2. They protect the young plant when it is most vulnerable
3. They provide food for the embryo until it can produce its own food
4. They facilitate dispersal of the embryo

32. Seeds
Once a seed coat forms, most of the embryo’s metabolic activities cease
Germination cannot take place until water and oxygen reach the embryo
-Seeds of some plants have been known to remain viable for thousands of years

33. Seeds
Specific adaptations ensure that seeds will germinate only under appropriate conditions
-Some seeds lie within tough cones that do not open until exposed to fire

34. Seeds
-Some seeds only germinate when sufficient water is available to leach inhibitory chemicals from the seed coat
-Still other seeds germinate only after they pass through the intestines of birds or mammals

35. Fruits Fruits are most simply defined as mature ovaries (carpels)
-During seed formation, the flower ovary begins to develop into fruit
-It is possible, however, for fruits to develop without seed development
-Bananas are propagated asexually

36. Carpel (developing fruit)
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prior sporophyte generation
degenerating gametophyte generation
next sporophyte generation
Carpel
(developing
fruit)
Stigma
Style
Pericarp
(ovary wall)
Exocarp
Mesocarp
Endocarp
Developing
seed coat
Embryo
Ovary
Part of
ovary
developing
into seed
Endosperm (3n)

37. Fruits The ovary wall is termed the pericarp
-Has three layers: exocarp, mesocarp and endocarp
-Their fate determines the fruit type
Fruits can be:
-Dry or fleshy
-Simple (single carpel), aggregate (multiple carpels), or multiple (multiple flowers)

38. Split along two carpel edges (sutures) with seeds attached
to edges; peas, beans. Unlike fleshy fruits, the three tissue
layers of the ovary do not thicken extensively. The entire
pericarp is dry at maturity.
The entire pericarp
is fleshy, although
there may be a thin
skin. Berries have
multiple seeds in
either one or more
ovaries. The
tomato flower had
four carpels that
fused. Each carpel
contains multiple
ovules that develop
into seeds.
Legumes
Stigma
Style
Seed
Outer pericarp
Fused
carpels
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Pericarp
True Berries

39. Drupes Samaras Pericarp Single seed enclosed Exocarp (skin) in a hard
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Seed
Single
seed
enclosed
in a hard
pit; peaches,
plums, cherries.
Each layer of the
pericarp has a
different structure
and function, with
the endocarp forming
the pit.
Not split and
with a wing
formed from the
outer tissues;
maples, elms,
ashes.
Pericarp
Exocarp (skin)
Drupes
Endocarp (pit)
Mesocarp
Samaras

40. Aggregate Fruits Multiple Fruits Sepals of a Derived from
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Ovary
Sepals of a
single flower
Derived from
many ovaries of
a single flower;
strawberries,
blackberries.
Unlike tomato,
these ovaries
are not fused
and covered by
a continuous
pericarp.
Individual flowers
form fruits around
a single stem. The
fruits fuse as seen
with pineapple.
Seed
Aggregate Fruits
Main stem
Pericarp of
individual flower
Multiple Fruits

41. Fruits
Developmentally, fruits are fascinating organs that contain 3 genotypes in one package:
-The fruit and seed coat are from the prior sporophyte generation
-The developing seed contains remnants of the gametophyte generation
-The embryo represents the next sporophyte generation

42. Fruit Dispersal Occurs through a wide array of methods
-Ingestion and transportation by birds or other vertebrates
-Hitching a ride with hooked spines on birds and mammals
-Burial in caches by herbivores
-Blowing in the wind
-Floating and drifting on water

44. Germination
Germination is defined as the emergence of the radicle (first root) from the seed coat
Germination begins when a seed absorbs water & oxygen is available for metabolism
-Often requires an additional environmental signal such as specific wavelength of light
-Or appropriate temperature
-Or stratification (period of low temperature exposure

45. Germination
Germination can occur over a wide temperature range (5o-30oC)
Some seeds will not germinate even under he best conditions
-The presence of ungerminated seeds in the soil of an area is termed the seed bank

46. Germination Germination requires energy sources such as:
-Starch stored in amyloplasts, proteins, or fats and oils
In cereal grain kernels, the single cotyledon is modified into a massive scutellum
-Its abundant food is used first during germination
-Later it serves as a conduit from the endosperm to the rest of the embryo

47. Germination Embryo produces gibberellic acid
-This hormone signals the aleurone (outer endosperm layer) to produce a-amylase
-Breaks down the endosperm’s starch into sugars that are passed to embryo
Abscisic acid, another hormone, can inhibit starch breakdown
-Establishes dormancy

48. 1. Gibberellic acid (GA) binds
to cell membrane receptors
on the cells of the aleurone
layer. This triggers a signal
transduction pathway.
Pericarp
Aleurone
Endosperm
Scutellum
(cotyledon)
Embryo
Starch
Sugars
Gibberellic
acid
-amylase
Aleurone cell
Signaling pathway
GA receptor GA
DNA
Myb protein
Transcription
and translation
Transcription and translation
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2. The signaling pathway
leads to the transcription of
a Myb gene in the nucleus
and translation of the Myb
RNA into Myb protein in
the cytoplasm.
3. The Myb protein then
enters the nucleus and
activates the promoter for
the -amylase gene,
resulting in the production
and release of -amylase.

49. Germination
As the sporophyte pushes through the seed coat, it orients with the environment such that the root grows down & shoot grows up
-Usually, the root emerges before the shoot
-The shoot becomes photosynthetic, and the postembryonic phase is under way
Cotyledons may be held above or below the ground
-May become photosynthetic or shrivel

50. a. b. Hypocotyl Secondary roots Primary roots Seed coat Cotyledon
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Hypocotyl
Secondary roots
Primary roots
Seed coat
Cotyledon
Withered
cotyledons
Plumule
Scutellum
Primary root
Adventi-
tious root
Radicle
Coleorhiza
First leaf
Coleoptile
Epicotyl
First leaves