1. Chapter 9: Plant Biology
9.3 Growth in Plants
Chapter 9: Plant Biology

2. Root Cross Section Pith – usually soft (sometimes solid) – storage
Procambium – cell layer that produces the vascular tissues
Periclycle – layer that may produce the roots
Endodermis – layer that surrounds the vascular bundle
Parenchyma – the bulk of the roots; storage; involved in conducting water from the soil in to the interior tissue
Epidermis – outer layer

3. Stem Cross Section
Epidermis – provides protection; pores for gas exchange
Xylem – in woody plants also proved support
Cambium – separates the xylem and phloem area of rapidly
dividing cells that differentiate into xylem or phloem

4. Plants show growth throughout their lives (indeterminate growth), however, they do die
Death occurs based on the plant’s life cycle
Some plants are annuals – they complete their life cycle in one year
Biennials – take 2 years to complete their life cycle
Perennials – live many years- usually die because of infections or other environmental factors

5. Meristems Growth in plants in confined to regions known as meristems
Meristem – the undifferentiated tissues in plants (like stem cells!)

6. Apical Meristem
Found at the tips of roots and stems, and the tips of buds and shoots
Produces primary growth (i.e. longer stem or roots)

7. Apical Meristems Root Meristem -responsible for the growth of the root
Shoot meristem is responsible for
Growth (lengthening) of stem
Cells that will produce leaves and flowers

8. With each division, one cell remains in the meristem
The other increases in size and differentiates as it is pushed away from the meristem region
Each apical meristem can give rise to additional meristems:
Protoderm  epidermis
Procambium  vascular tissue
Ground meristem  pith

9. (cambium)
(epidermis)
(pith)

10. Lateral Meristems Found in the cambium
Allow for secondary growth (i.e. for the plant to get thicker)

13. Auxin
Auxins are hormones that have a broad range of function including initiating root growth, development of fruit, and regulating leaf development
IAA (indole-3-acetic acid) is the most abundant auxin
IAA is produced in the apical meristem and is transported down the stem to stimulate growth
At high concentrations it can inhibit growth

14. Axillary buds are shoots that form at a node (the junction of the stem and the base of a leaf).
Auxin produced at the shoot apex inhibits growth at the nodes. This is known as apical dominance.

15. As the plant grows the shoot apex is further away from the node
This means less auxin means the node can now grow
Now the axillary bud can produce a stem or a fruit
Cytokinins are hormones produced in the roots that also promote axillary bud development

16. Plant Tropisms A tropism is a growth in response to a stimulus
Phototropism: the growth in response of light
Gravitropism: growth in response to a gravitational force

17. Phototropism and Auxin
Plants require light for photosynthesis; thus seedlings must grow toward sunlight
Auxins cause the positive phototropism of plant shoots and seedlings (so long as the plant cells have auxin receptors)

18. Auxin increases the flexibility of plant cell walls enabling cell elongation on the side of the shoot necessary to cause growth towards the light.
Auxin is actually concentrated on the side of the stem away from the light source
The elongation of the cells on the side away from the light allows for curvature toward the light source.

20. Root auxin inhibits shoot elongation

21. Micropropagation of Plants
This is an in vitro procedure to clone plants
Tissues from the shoot apex of a plant with desirable features is sterilized and cut into pieces known as explants
The explants are grown in a nutrient agar that also contains growth hormones.
Once the roots and shoots are developed, the clones plant can be transferred to soil

23. Micropropagation
Useful for propagating virus-free plants, since meristematic tissues are likely virus-free.
Can be used to clone endangered plants
Some plants, like orchids, are difficult to germinate the traditional way. Micropropagation is high successful.
The plantlets can be stored in liquid nitrogen - cryopreservation

24. 9.4 Reproduction in Angiospermophytes

26. Dicotyledonous Flower Parts
FUNCTION
Sepals
Protect the developing flower while in the bud and at night when the buds close.
Petals
Modified leaves; often colourful to attract pollinators
Stamen
The “male” reproductive structure; made of anther and filament
Anther
Produces and releases pollen
Filament
Stalk of stamen that holds up anther
Carpel
The “female” reproductive structure; made of ovary, style, and stigma

27. Pistil
Can refer to a single carpel or a group of fused carpels
Stigma
Sticky top of carpel which pollen lands on
Style
Supports and holds up the stigma; gives the stigma exposure to pollen
ovary
Base of carpel in which the female sex cells develop; if fertilization occurs, it will turn into a protective fruit
Ovules
Found in the ovary; contain female sex cells, eggs
Pollen
Contain male sex cells (sperm)

28. Flowers occur in various colours, shapes and types – reflective of their pollinator
Complete flowers – contain all four basic flower parts (sepals, petals, stamen, and carpel)
Incomplete flowers – lack at least one of these parts
Staminate flowers – have only stamens
Carpellate flowers – have only carpets

29. Pollination
the process in which pollen (which contains the male sex cells –sperm) is placed on the female stigma.
Can occur via a variety of vectors
Wind
water
Insects
Birds
Bats

30. Angiosperms and their pollinators have coevolved (supported by fossil evidence)
The flowers colours, patterns, odours, shapes and even the time of day it blooms are designed to attract a specific pollinator
Often, the flower provides the gift of food to the pollinator in exchange for the pollinator unintentionally transporting pollen to the stigma. A mutualistic relationship!

31. Examples Red flowers – pollinated by birds
Yellow and orange flowers – bees
Heavily scented flowers – nocturnal animals
Inconspicuous, odourless flowers – wind

32. As the humming bird eats nectar at the base of the flower, it picks up pollen which it will transfer to the stigma of the next flower it visits

33. These orchids look similar to a particular wasp species
These orchids look similar to a particular wasp species. A wasp will come to the orchid and a attempt to mate with it. In the process it will pick up pollen and transfer it to the next flower it attempts to mate with.

34. Cross Pollination – pollen lands on the stigma of a different plant.
Self Pollination – when pollen from the anther of a plant falls on its own stigma
A form of inbreeding – thus less genetic variation
Cross Pollination – pollen lands on the stigma of a different plant.
Increases variation and offspring with different fitness

35. Fertilization
When the male and female sex cells unite to form a diploid zygote.
The female sex cells are in the ovules. The sperm from the pollen that has attached itself to the stigma must make its way to the ovules in the ovary.

36. Pollen attaches to stigma and begins to grow a pollen tube through the style
Within the growing pollen tube is the nucleus that will produce the sperm.
The pollen tube completes growing by entering an opening at the bottom of the ovary
The sperm moves from the tube to combine with the egg of ovule to form a zygote.

39. The Seed and Seed Dispersal
Once the zygote is formed, it develops with the surrounding tissue into the seed
As the seed is developing, the ovary around the ovule mature into a fruit
Seed dispersal can be aided by water, wind, animals

41. SEED
Is the means by which an embryo can be dispersed into to distant locations.
It is a protective structure for the embryo

43. Seed Part
Function
testa
Tough, protective outer coat
cotyledons
Seed leaves that function as nutrient storage structures
microphyle
Scar of the opening where the pollen tube entered the ovule
Embryo root and embryo shoot
Become the new plant when germination occurs

44. Pre-Germination Once seeds are formed, a maturation process follows.
The seed dehydrates until the water content of the seeds is about % of its weight.
At this point, the seed goes into a dormant period where there is low metabolism and no growth or development.
Duration is variable for different types of seed
It is an adaptation to environmental conditions

45. FUN FACT In 1995, a team of biologists found some seeds in a dried-up
lakebed. The seeds were from a type of lotus
plant. After germinating some of the seeds,
the biologists found them to be nearly 1300
years old!!! (They used radiometric dating to
determine this age.)

46. Fun Fact
In 2005, a 2000 year old Judean Date palm (found in the ruins of Herod the Great’s palace)was germinated

47. Germination Conditions
If conditions become favourable, the seed will germinated.
GERMINATION – is the development of the seed into a functional plant.
There are several conditions that must be fulfilled for a seed to germinate.

48. WATER Required to rehydrate the dried seed tissues
Makes the seed swell
As a result the seed coat will crack and hydrolytic enzymes are activated- they will start to catabolize large molecules (storage polysaccharides such as starch is converted into maltose) for cellular respiration.

49. OXYGEN
Required for the break down of those sugars in cellular respiration

50. TEMPERATURE
Appropriate temperature is required, that is varied among plants depending on their natural environment.
Ex. Period of low temperature followed by high temps – ensures that the seed does not geminate until the winter has passed.
Temperature is important for enzyme activity

51. Many plants have specific conditions other than these that must be met in order to germinate.
Ex:Lodgepole Pine

52. The emerging seedling is fragile and will be exposed to hard weather, parasites, predators, and other hazards.
Many seeds will not produce a functional plant because of these threats
To compensate, plants produce a large number of seeds

53. Metabolic Processes during Germination of a Starchy Seed
Seed absorbs water (which leads to many metabolic changes)
Gibberellin is released after the uptake of water
Gibberellin – plant growth hormone

54. Gibberellin triggers the release of the enzyme amylase
Amylase causes the hydrolysis of the starch into maltose
Maltose is hydrolyzed into glucose which can be used for cellular respiration or converted into cellulose to build cell walls for new cells

55. Stored proteins and lipids will also be hydrolyzed to make proteins/enzymes and phospholipids and energy metabolism.
Germination uses the food stored in cotyledons to grown until it reaches light when it starts to photosynthesize

57. Control of Flowering Light important factor for growth and development
Plants are able to detect the presence of light, its direction, wavelength, intensity
PHOTOPERIODISM – the plant’s response to light involving the relative lengths of day and night.

58. *To ensure continued existence in an area, a plant must flower when pollinators are available and when necessary resources are plentiful

59. PLANT TYPE
FLOWERING AND LIGHT
EXAMPLES
LONG-DAY PLANTS
Bloom when days are longest and nights the shortest (midsummer)
- Require Pfr
Radishes, spinach, lettuce
SHORT-DAY PLANTS
Bloom in spring, late summer, and autumn when days are shorter
- Inhibited by Pfr
Poinsettias, chrysanthemums, asters
DAY-NEUTRAL PLANTS
Flower without regard to day length
Roses, dandelions, tomatoes

60. It is actually the length of night that controls the flowering process.
The control is brought about by a special blue-green pigment called phytochrome.

61. Phytochrome Phytochrome is a photoreceptor and a pigment
It absorbs light
There are 2 forms of phytochrome
Pr – absorbs red light
Pfr – absorbs far-red light/darkness

62. Far-Red Light Wavelengths between 700-800nm
At the far end of the visible light spectrum
(Between red light and infrared light)

63. During the day, when there is light, red light (wavelength of 660nm) is present
Pr absorbs red light and is rapidly converted into Pfr
At the end of the day, after many hours of light, plants will have most of their phytochrome in the form of Pfr

64. During the night, when there isn’t light (therefore no red light), Pfr is slowly converted back into Pr
By morning, most of the phytochrome will be Pr again
If there is even a flash of light interrupting the darkness during the night, it will disrupt the process of Pfr turning into Pr

65. Pr Pfr _____________________________________________________________ Pfr Pr

66. Long-day plants, require Pfr to flower
Long day = short night!
At the end of a short night, there will still be lots of Pfr remaining.
The remaining Pfr at the end of a short night stimulates the plant to flower.

67. In short-day plants, the Pfr acts as an inhibitor for flowering.
So after a short night, the remaining Pfr will prevent the plant from flowering.
If it was a long night, all the phytochrome will be in the form of Pr (there will be no Pfr) so flowering CAN occur.