1. Physiology of Seed Plants

2. Regulating Growth and Development: The Plant Hormones
Auxins
Cytokinins
Ethylene
Abscisic Acid
Gibberellins

3. Hormones
Chemical signals that help both plants and animals regulate and coordinate metabolism, growth, and differentiation.
Phytohormones- plant hormones

4. Three basic elements of Hormones
Synthesis of the hormone in one part of the organism
Transport of the hormone to another part (target tissue)
Induction of chemical response

5. Phytohormones Produced in tissues or glands
Very active in small quantities
Pineapple Ananas comosus for example are only 6 micrograms of indoleacetic acid (IAA) a common plant hormone per kg of plant material. (analogous to a needle in 20 metric tons)
Can stimulate or inhibit depends on chemical structure and how it is read by the target tissue

6. Five classes of plant hormones The “Classic Five”
Auxins- today
Cytokinins- today
Ethylene- thursday
Abscisic acid- thursday
Gibberellins- thursday

7. Auxins
Charles Darwin and Francis Darwin- The Power of Movement in Plants 1881
In response to light
an “influence” that causes
bending is transmitted
from the tip to area below
the tip

8. The Principle naturally occuring Auxin- Indoleacetic Acid
In plants variety of pathways to produce
tryptophan usually precursor
All tissue produces IAA but typically
found in shoot apical meristems, young
leaves and developing fruit and seeds.
Mutants lacking either auxin or cytokinin
Have yet to be found- mutations eliminating
Them are lethal

9. Auxin synthesis- the site of auxin
synthesis along the margin of a
young leaf
Site corresponds to the location
of cells that will differentiate into
a hydothode (gland like structure)
GIS reporter gene detects auxin
synthesis

10. Auxin transport- experimental demo of polar auxin transport in
stems represented here by a segment of hypocotyl from a
seedling

11. In the root, nonpolar transport of IAA takes place in
the phloem of the vascular cylinder whereas the polar transport
occurs in the epidermis and cortical parenchyma cells

12. Schematic model for polar auxin transport

13. IAA induced xylem regeneration around a wound
Arrowhead- vascular regeneration
Basipetal polar movement of auxin from
Above the arrow and then around the wound
IAA induced xylem regeneration around a wound

14. - When the apical bud is cut off a plant, the development of axillary buds in lateral branches is observed.
- If the apical bud is replaced by cotton impregnated with auxin, no axillary bud development is observed.
- So the auxin replaces the apical bud. - It can be deduced that this hormone is produced in the apical part of the plant.

15. The inferior part of the plant including roots ( or root cap) is cut off and the plant is
put in a medium containing auxin or free of it.
Without auxin, adventitious roots can developed. This is the principle of cuttings.
However, with auxin, root development is much better.

16. Auxin promotes fruit development
Auxin is involved with the formation of fruit
Parthenocarpic fuit- by treating a female flower parts (carpels) of certain species with auxin it is possible to produce a fruit (without fertilization- a virgin fruit) i.e. seedless tomatoes, cucumbers and eggplants.
Developing seed is a source of auxin

17. Auxin and fruit development- Normal strawberry

18. Strawberry with all seeds removed

19. Strawberry with horizontal band of seeds removed

20. Other characteristics of Auxin
Auxin provides chemical signals that communicate information over long distances
Promotes the formation of lateral and adventitious roots
Synthetic auxin (2,4 dichlorophenoxyacetic acid) are used to kill weeds (broad leaf)
Mechanism unk.

21. Cytokinins
In 1941 Johannes van Overbeek found that coconut milk (liquid endosperm) contained potent growth factors
Factors greatly accelerated the development of plant embryos and promoted the growth of isolated tissue and cells in vitro (test tube)

22. Discovery had two affects
It gave impetus to studies of isolated plant tissues
Launched the search for another major group of growth regulators

23. Basic medium used for tissue culture of plant cells
Contained sugar
Vitamins
Various salts
Grown in this culture, growth slowed or stopped
Thus some growth stimulus declined and the addition of IAA had no affects
Adding coconut milk encouraged the cells to divide and growth to resume

24. Growth factor from DNA
Isolation of growth factor from DNA identifying its chemical nature called kinetin and the group of regulators called cytokinins because its involvement with cytokinesis

25. Kinetin Resembles purine- adenine
Probably does not occur naturally in plants
Has relatively simple structure
Chemist able to synthesize a number of related compounds
Zeatin- most active naturally occurring cytokinin (maize)

27. Cytokinins
Found in active dividing structures, seeds, fruits, leaves and root tips
Found also in SVP horsetail, fern
Central to tissue culture methods and extremely important in biotech.
Tx of lateral buds causes growth even in the presence of auxin thus modifying apical growth.

28. Undifferentiated plant cell has two courses open to it
The cytokinin/auxin ratio regulates the production of roots and shoots in tissue cultures
Undifferentiated plant cell has two courses open to it
It can enlarge, divide, enlarge and divide again (undifferentiate) or
without undergoing cell division, it can elongate and differentiate

29. In tobacco stem tissue
Applicatin of IAA causes rapid cell expansion- giant cells are formed
Kinetin alone has little or no effect
IAA + Kinetin results in rapid cell division, so that large numbers of relatively small, undifferentiated cells are formed.
High IAA, callus tissue- a growth of undiff. Cells in tissue culture frequently gives rise to roots.

30. Callus development- effects of increasing [IAA] at various kinetin

31. - At the top, the apical dominance have been annulled by cutting the apical bud. - At the centre, the terminal bud and the root cap have been cut. No futher development of axillary buds on the explant can be observed. So the roots are necessary for the development of buds.
- on the other hand (at the bottom), if one identical explant is introduiced in a medium containing cytokinins, the development of axillary buds occurs. So the cytokinins replace the roots and it can be deduced that these hormones are produced in the roots.
It is observed also that there is less root development in the presence of cytokinins.

32. Summary
Auxins:
- They are produced in the apical part of the plant. - They prevent the development of the axillary buds. - They favour the rhizogenesis ...(development of roots).
Cytokinins:
- They are produced in the roots. - They prevent the development of roots. - They favour the development of the axillary buds.

34. With large concentrations of cytokinins and low concentrations of auxins, the development of axillary or adventitious buds can be obtain and in this way the plants are multiplied.
With large concentrations of auxins and low concentrations of cytokinins or no cytokinins, the rooting of the shoots can be arrived at.
- With equal concentrations of the two hormones, a callus is obtain. The callus is the result of the anarchic proliferation of cells which are more or less differentiated but which cannot organized them and form tissues and distinct organs.

36. Cytokinins delay leaf senescence
Yellowing (loss of chlorophyll) of leaf can be delayed with the addition of cytokinins
Xanthium strumarium Leaves turned yellow in about ten days in plain water
Add 10mg of kitenin help retain green

37. Additional chemicals used by plants
Brassinosteroids- naturally occuring polyhydroxyl steroids (tissue growth)
Salicylic acid- phenolic compound similar structure to aspirin implicated in defense responses
Jasmonates- class of compounds known as oxylipins plant growth regulation and defense
Polyamines- strongly basic molecules found in all organisms (bacteria, fungi, animal, plants) are essental for growth and development and affects cell division
Systemin- a polypeptide functions as a long distance signal to activate chemical defenses against herbivores.
Nitric oxide (NO) serves as a signal in hormonal defense responses.

38. Ethylene Plays a role in fruit ripening
Promotes abscission (shedding of leaves, flowers and fruit)
Triggers enzymes that promote fruit loosening from trees
Auxin prevents abscission (prevents preharvest)
High concentration does the opposite

39. Abscisic Acid (ABA) First discovered as dormin and abscisin
Dormin ash and potatoes
In other plants abscisin
Identical compounds now called Abscisic acid

40. Abscisic Acis Levels increase during early seed development
Stimulates the productio of seed storage protein
Prevents premature seed germination
Decline in ABA leads to germination

41. Gibberellin Found in immature seeds- highest concentration
Stimulates cell division and cell elongation
Application to dwarf mutants cause them to grow tall
Plays a role in breaking seed dormancy and germination