Hormone, Auxin, Role of phyto hormones, Function of auxin Function of cytokinins Tissue culture

1. Plant Hormones
VSC – 503, Growth and Development of Vegetable Crops
Department of Horticulture (Vegetable Science)
College of Agriculture
Central Agricultural University, Imphal
Submitted By: - Aditya Parashar – 38A-22(m)
Debiya Leitanthem – 05A-22(m)

2. INTRODUCTION
Plant hormones are endogenous organic compounds active at very low
concentration, produced in one tissue, and translocated to another point
in the plant where their effects on growth and development are
manifested.
Julius Von Sachs gave the first idea on plant hormones.
An endogenous compound, which is synthesized at one site and
transported to another site where it exerts a physiological effect in
very low concentration.
But ethylene (gaseous nature), exert a physiological effect only at a
near a site where it is synthesized.
So, classified definition of a hormone does not apply to ethylene.

3. Plant "hormones" are sometimes preferentially referred to as plant
growth regulators (PGR) because they differ from animal hormones in
the following ways:
i. Plant hormones are not made in specialized tissues
ii. Plant hormones do not have specific target tissues
iii. Plant hormones usually do not have specific effects
Cont….

4. Site of synthesis
4
• The primary site of action of plant growth hormones at the molecular level
remains unresolved.
Reasons
• Each hormone produces a great variety of physiological responses.
• Several of these responses to different hormones frequently are similar.
• The response of a plant or a plant part to plant growth regulators may vary
with the variety of the plant.
• Even a single variety may respond differently depending on its age,
environmental conditions and physiological state of development (especially
its natural hormone content) and state of nutrition. There are always
exceptions for a general rule suggesting the action of a specific growth
regulator on plants.
• There are several proposed modes of action in each class of plant hormone,
with substantial arguments for and against each mode.

5. Hormone Group
5
Growth Promoters
• Auxin - Substances generally resembles IAA and has the ability to stimulate
the elongation of coleoptiles.
• Gibberellins - are diterpenoids, which have the ability to elongate the stem
of green seedlings especially certain dwarf and rosette types.
• Cytokinin - Usually substituted Adenines, which resembles zeatin (Naturally
occurring cytokinin in Zea mays) and have the ability to stimulate
cytokinensis in cultures of tobacco cells.

6. Growth Inhibitors
They are regulators of growth, which originally depress the growth.
• Ethylene - Gaseous regulator that stimulate is diametric growth in the apices of
dicot seedlings.
• Abscisic Acid – They are called stress hormone and they usually suppress the
growth in case of any stress condition.
6

7. In 1919, A. Paál provided evidence that the growth promoting stimulus produced
in the tip was chemical in nature. Bending here occurs without sunlight so its due
to chemical.
In 1926, F. W. Went showed that the active growth promoting substance can
diffuse into a gelatin block. He also devised a coleoptile-bending assay for
quantitative auxin analysis.
7
Auxin and Its Discovery

8. There are two pathways-
The Tryptophan dependent pathway
1. The indole-3-acetamide pathway (IAM )
2. The indole-3-acetonitrile pathway (IAN)
3. The tryptamine pathway (TAM)
4. The Bacterial pathway
The Tryptophan independent pathway.
8
Biosynthesis of Auxin

9. Tryptophan Dependent Pathway
9
Biosynthesis of Auxin

10. 10
Occurrence of Auxins
Naturally Occurring Auxins
• Indole-4 acetic acid (IAA)
Synthetic
• 2,4-D (2,4-Dichlorophenoxy Acetic Acid)
• 2,,4,5-T (2,4,5-Trichlorophenoxy Acetic Acid)
• NAA (Naphthalene Acetic Acid)
Auxins in a plant body is synthesised in Meristems > Young Leaves >
Developing Fruits and Seeds

11. 11
Physiological effects of Auxins
1. Cell elongation
2. Maintenance of apical dominance
3. Auxin promotes formation of lateral and adventitious roots
4. Stimulates abscission (in young fruits) and Delays abscission (in mature
fruits)
5. Auxin promotes fruit development
6. Induces vascular differentiation
7. Auxin transports, regulates floral bud development and leaf abscission

12. 12
Physiological effects of Auxins
Strawberry fruit is actually a swollen receptacle whose growth is regulated by
auxin produced by the seeds, which are achenes-the true fruits. When the
achenes are removed, fruit fails to develop normally. Spraying the achene
less receptacle with IAA restores normal growth and development.
A normal fruit and one with achenes removed Achenes removed, sprayed with auxin

13. Gibberellins and Its Discovery
13
In 1898, Shotaro Hori suggested that the disease was caused by a fungus
that infected the rice.
Eiichi Kurosawa, a Japanese scientist in 1926 was able isolate
secretions from the fungus Gibberella fujikuroi. It causes foolish seedling
(bakanae) disease in rice.
The secretions caused the same symptoms when applied to other rice
plants.
In 1934, Teijiro Yabuta isolated the active substance and named it
gibberellin.
Gibberellins are terpenoid derivatives. Terpenoids are compounds
made from assembly of isoprene units.

14. Con…
14
GA3-Oxidase is the final enzyme in GA synthesis while GA 2-Oxidase
inactive the biologically
There are three biologically active Gibberellins GA1, GA3 and GA4.
Biosynthesis of Gibberellin
Gibberellic acids are synthesized in: -
• Immature seeds,
• The root and shoot apical meristems,
• Young leaves.

15. Physiological Role of Gibberellin
15
• Gibberellins stimulate cell elongation.
Ex: Stem growth in dwarf and rosette Plants (Cabbage, a long-day plant,
remains as a rosette in short days, but it can be induced to bolt and Flower
by applications of gibberellin.
• Gibberellins regulate the transition from juvenile to adult phase.
• Gibberellins influence Floral Initiation and Sex determination.
Ex: In maize, it suppress stamen development and induce pistillate flowers
whereas in dicots like cucumber, spinach etc., it gives opposite effect.
• Gibberellins promote fruit set.
• Gibberellins Promote Seed Germination.

16. Kinetin was discovered by Skoog and Miller (1950) from the tobacco pith callus
and the chemical substance was identified as 6-furfuryl aminopurine. Because of
its specific effect on cytokinesis (cell division), it was called as cytokinins or
kinetin. The term, cytokinin was proposed by Letham (1963).
Fairley and Kingour (1966) used the term, phytokinins for cytokinins because
of their plant origin.
Chemically cytokinins are kinins and they are purine derivatives.
Cytokinins, besides their main effect on cell division, also regulate growth and
hence they are considered as natural plant growth hormones.
16
Cytokinins (Kinetins)

17. Occurrence of Cytokinins
20XX presentation title 17
Cytokinins can be extracted from coconut milk (liquid endosperm of coconut),
tomato juice, flowers and fruits of Pyrus malus; fruits of Pyrus communis
(Pear), Prunus cerasiferae (plum) and Lycopersicum esculentum (bhendi);
Cambial tissues of inus radiata, Eucalyptus regnans and Nicotiana tabacum;
immature fruits of Zea mays, Juglans sp. and Musa sp; female gametophytes
of Ginkgo biloba; fruitlets, embryo and endosperms of Prunus persica;
seedling of Pisum sativum; root exudates of Helianthus annuus and tumour
tissues of tobacco. According to Skoog and Armstrong (1970), at least seven
well established types of cytokinins have been reported from the plants.
Some of the very important and commonly known naturally occurring
cytokinins are Coconut milk factor and Zeatin. It was also identified that
cytokinin as a constituent of t-RNA.

18. Biosynthesis of Cytokinins
18
It is assumed that cytokinins are synthesized as in the case of purines in
plants (nucleic acid synthesis). Root tip is an important site of its synthesis.
However, developing
seeds and cambial tissues are also the site of cytokinin biosynthesis.
Kende (1965) reported that cytokinins move upwards perhaps in the xylem
stream. However, basipetal movement in petiole and isolated stems are also
observed. Seth et al (1966) found that auxin enhances kinetin movement
(translocation) in bean stems.
Some of the very important and commonly known naturally occurring
cytokinins are Coconut milk factor and Zeatin. It was also identified that
cytokinin as a constituent of t-RNA.

19. Physiological effects of cytokinins
19
• Cell division
The most important biological effect of kinetin on plants is to induce cell
division especially in tobacco pith callus, carrot root tissue, soybean
cotyledon, pea callus etc.
• Cell enlargement
Like auxins and gibberellins, the kinetin may also induce cell enlargement.
Significant cell enlargement has been observed in the leaves of Phaseolus
vulgaris, pumpkin cotyledons, tobacco pith culture, cortical cells of tobacco
roots etc.
• Concentration of apical dominance
External application of cytokinin promotes the growth of lateral buds and
hence

20. Physiological effects of cytokinins
20
• Dormancy of seeds
Like gibberellins, the dormancy of certain light sensitive seeds such as lettuce
and tobacco can also be broken by kinetin treatment.
• Delay of senescence (Richmand - Lang effect)
The senescence of leaves usually accompanies with loss of chlorophyll and
rapid breakdown of proteins. Senescence can be postponed to several days
by kinetin treatment by improving RNA synthesis followed by protein
synthesis. Richmand and Lang (1957) while working on detached leaves of
Xanthium found that kinetin was able to postpone the senescence for a
number of days.

21. Physiological effects of cytokinins
21
• Flower induction
Cytokinins can be employed successfully to induce flowering in short day
plants.
• Morphogenesis
It has been shown that high auxin and low kinetin produced only roots
whereas high kinetin and low auxin could promote formation of shoot buds.
• Commercial applications
Cytokinins have been used for increasing shelf life of fruits, quickening of root
induction and producing efficient root system, increasing yield and oil contents
of oil seeds like ground nut.

22. Ethylene is the only natural plant growth hormone exists in gaseous form.
Important physiological elects
1. The main role of ethylene is it hastens the ripening of fleshy fruits eg. Banana,
apples, pears, tomatoes, citrus etc.
2. It stimulates senescence and abscission of leaves
3. It is effective in inducing flowering in pine apple
4. It causes inhibition of root growth It stimulates the formation of adventitious
roots
5. It stimulates fading of flowers
6. It stimulates epinasty of leaves.
22
Ethylene

23. Addicott (1963) isolated a substance strongly antagonistic to growth from young
cotton fruits and named Abscission II. Later on this name was changed to
Abscisic acid. This substance also induces dormancy of buds therefore it also
named as Dormin.
Abscisic acid is a naturally occurring growth inhibitor.
23
Abscisic acid
Physiological effects
The two main physiological effects are besides other effects
1. Geotropism in roots
2. Stomatal closing
1. Geotropism in roots
Geotropic curvature of root is mainly due to translocation of ABA in basipetal
direction towards the root tip.

24. 24
2. Stomatal closing
ABA is synthesized and stored in mesophyll chloroplast. In respond to water
stress,
the permeability of chloroplast membrane is lost which resulted is diffusion of ABA
out of
chloroplast into the cytoplasm of the mesophyll cells. From mesophyll cells it
diffuses into
guard cells where it causes closing of stomata.
Cont…
3. Other effects
• Including bud dormancy and seed dormancy
• Includes tuberisation
• Induces senescence of leaves fruit ripening, abscission of leaves, flowers and
fruits
• Increasing the resistance of temperate zone plants to frost injury.

25. References
https://gcwgandhinagar.com/econtent/document/158717928
4Unit%205.1%20Plant%20Growth%20Regulators%20-
Auxins.-.pdf
https://academic.oup.com/jxb/article/63/8/2853/734272
Some notes
https://byjus.com/biology/plant-growth-
regulators/#:~:text=The%20first%20phytohormone%20to%
20be,IAA%20and%20other%20related%20compounds.
https://www.sciencedirect.com/topics/nursing-and-health-
professions/phytohormone#:~:text=Plant%20hormones%20
(phytohormones)%20are%20chemicals,of%20plants%20to
%20environmental%20stimuli.
20XX presentation title 25

26. Thank you