1. Plant Growth

2. Growth in Animals Animals grow throughout the whole organism
many regions & tissues at different rates

3. Growth in Plants Specific regions of growth: meristems
stem cells: perpetually embryonic tissue
regenerate new cells
apical shoot meristem
growth in length
primary growth
apical root meristem
lateral meristem
growth in girth
secondary growth

4. Apical meristems
shoot
root

5. Root structure & growth
protecting the meristem

6. protecting the meristem
Shoot growth
Apical bud & primary growth of shoot
region of stem growth
axillary buds
“waiting in the wings”
protecting the meristem
Young leaf
primordium
Apical meristem
Older leaf
primordium
Lateral bud
primordium
Vascular tissue

7. Growth in woody plants Woody plants grow in height from tip
Primary
xylem
Growth in woody plants
Woody plants grow in height from tip
primary growth
apical meristem
Woody plants grow in diameter from sides
secondary growth
lateral meristems
vascular cambium
makes 2° phloem & 2° xylem
cork cambium
makes bark
Primary
phloem
Epidermis
Lateral
meristems
Secondary
xylem
Primary
phloem
Primary
xylem
Secondary
phloem
Annual
growth
layers
Bark

8. Secondary growth Secondary growth growth in diameter
thickens & strengthens older part of tree
cork cambium makes bark
growing ring around tree
vascular cambium makes xylem & phloem

9. Why are early & late growth different?
Vascular cambium
Phloem produced to the outside
Xylem produced to the inside
bark
phloem
cork cambium
xylem
late
vascular cambium
early
last year’s xylem

10. Woody stem How old is this tree? cork cambium vascular cambium late
early 3 2 1
xylem
phloem
bark

11. Tree trunk anatomy tree girdling What does girdling do to a tree?
Aaaargh!
Murderer!
Arborcide!
Tree trunk anatomy
tree girdling
What does girdling do to a tree?

12. Where will the carving be in 50 years?

13. Plant hormones
auxin
gibberellins
abscisic acid
ethylene
and more…

14. Auxin (IAA) Effects controls cell division & differentiation
phototropism
growth towards light
asymmetrical distribution of auxin
cells on darker side elongate faster than cells on brighter side
apical dominance

15. Gibberellins Family of hormones Effects
over 100 different gibberellins identified
Effects
stem elongation
fruit growth
seed germination
plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

16. Abscisic acid (ABA) Effects slows growth seed dormancy
high concentrations of abscisic acid
germination only after ABA is inactivated or leeched out
survival value: seed will germinate only under optimal conditions
light, temperature, moisture

17. One bad apple spoils the whole bunch…
Ethylene
Hormone gas released by plant cells
Effects
fruit ripening
leaf drop
like in Autumn
apoptosis
One bad apple spoils the whole bunch…

18. Fruit ripening Adaptation Mechanism
hard, tart fruit protects developing seed from herbivores
ripe, sweet, soft fruit attracts animals to disperse seed
Mechanism
triggers ripening process
breakdown of cell wall
softening
conversion of starch to sugar
sweetening
positive feedback system
ethylene triggers ripening
ripening stimulates more ethylene production

19. Apoptosis in plants Many events in plants involve apoptosis
What is the evolutionary advantage of loss of leaves in autumn?
Many events in plants involve apoptosis
response to hormones
ethylene
auxin
death of annual plant after flowering
senescence
differentiation of xylem vessels
loss of cytoplasm
shedding of autumn leaves
The loss of leaves each autumn is an adaptation that keeps deciduous trees from desiccating during winter when the roots cannot absorb water from the frozen ground. Before leaves abscise, many essential elements are salvaged from the dying leaves and are stored in stem parenchyma cells. These nutrients are recycled back to developing leaves the following spring. Fall color is a combination of new red pigments made during autumn and yellow and orange carotenoids that were already present in the leaf but are rendered visible by the breakdown of the dark green chlorophyll in autumn.
Photo: Abscission of a maple leaf.
Abscission is controlled by a change in the balance of ethylene and auxin. The abscission layer can be seen here as a vertical band at the base of the petiole. After the leaf falls, a protective layer of cork becomes the leaf scar that helps prevent pathogens from invading the plant (LM).

20. Responses are critical for plant success
Tropisms—growth of plant organs toward or away from stimuli
Phototrophism
Gravitropism
Thigmotrophism
Other Stimuli
Turgor movements
Environmental stress

21. Phototropism
Biological clocks control circadian rhythms in plants—cycle with a frequency of about 24 hours
Set due to environmental signals
Most cued by light-dark cycle resulting from earth’s rotation

22. Photoperiodism synchronizes plant response
Plants detect the time of year by the photoperiod
Photoperiodism controls flowering
Critical night length
If daytime is broken by brief peroids of darkness—plants flower (summer)
If night is interrupted by short exposure to light—plants do not flower (winter)

23. Phytochromes
Photoreceptors in many plant responses to light and photoperiod—help to measure length of darkness in a photoperiod
Phytochromes alternate between two photoreversible forms:
Pr—red absorbing
Pfr—far red absorbing

24. Phytochromes entrain biological clock
Pfr gradually reverts to Pr when light not present
Decrease in Pfr = night
Increase in Pfr = day

25. Gravitropism Orientation of a plant in response to gravity
Roots display positive gravitropism—curve down
Shoots display negative gravitropism—curve upward

26. Thigmotropism
Directional growth in response to touch

27. Turgor movements Rapid, reversible plant responses
Rapid leave movements—travel from the leaf that was stimulated to adjacent leaves along the stem
Sleep movements—lowering of leaves to a vertical position in evening and raising of leaves to a horizontal position
Due to daily changes in turgor pressure

28. Responses to Environmental Stress
Water Deficit
Oxygen Deprivation
Salt Stress
Heat Stress
Cold Stress

29. Water Deficit
Leaves and roots have control systems to cope with water deficits
Leaves—reduce transpiration
Roots—reduce growth

30. Oxygen Deprivation
Water logged soil lacks air spaces that provide oxygen
Some plants form air tubes that extend from roots to the surface

31. Salt stress
Excess salt in the soil can cause a water deficit in the plant and have toxic effects on the plant
Plants produce compatible solutes that keep the water potential of cells more negative than the soil solution.

32. Heat Stress
Transpiration helps plants respond to excessive heat—which can denature the enzymes and destroy the metabolism of the plant.
Plants can produce heat shock proteins when exposed to excessive temperatures—back up to transpiration

33. Cold Stress Cold causes a change in the fluidity of cell membranes
Subfreezing are the most severe form of cold stress because ice crystals begin to form in the plant
Plants respond by altering the lipid composition of their membranes

34. Defense against herbivores
Plants defend themselves both physically and chemically:
Physical—thorns and spines
Chemical—distasteful or toxic compounds
Recruit predatory animals to help defend

35. Defense against pathogens
The hypersensitive response (HR) contains the infection by:
Photoalexins—antimicrobial compounds released from wounded cells
Activation of genes encoding pathogen resistant (PR) proteins –act as signals to adjacent cells
Lignin synthesis and cross-linking of cell walls—actions aimed at isolating the infection.

37. Don’t take this lying down…
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