Expains in detail the Plant Growth Hormones, Plant growth promoters and plant growth retardants/inhibitors. The role of Growth hormones in Physiological process of Plants and their application in Plant Tissue culture (Auxins, cytokinins, Gibberellins, ABA, Ethylene)

1. Plant Growth Hormones
Dr. Deepa M.A
Assistant Professor of Botany
Government Arts College (Autonomous)
Coimbatore – 641 018
https://www.youtube.com/channel/UCXqGlEjNmKrTm
WVqMIngbDA
https://www.slideshare.net/DrDeepa6/

2. Introduction
• Plants also depend on certain organic compounds to signal, regulate and
control the growth of plants. These are collectively called as Plant Growth
Regulators or Plant Growth Hormones.
• Plant growth regulators can be defined as organic substances which are
synthesized in minute quantities in one part of the plant body and
transported to another part where they influence specific physiological
processes.

3. • Auxins were the first plant hormones discovered.
• Charles Darwin was among the first scientists to dabble
in plant hormone research.
• In his book "The Power of Movement in Plants" presented in
1880, he first describes the effects of light on movement of
canary grass (Phalaris canariensis) coleoptiles.

4. PLANT
GROWTH
REGULATORS
AUXINS CYTOKININS
GIBBERELLINS
ABSSISIC ACID
ETHYLENE

5. • Plant growth regulators are broadly classified into two major
groups:
1. Plant Growth Promoters
2. Plant Growth Inhibitors

6. AUXINS
• The term auxin is derived from the Greek word „auxein‟ which
means „to grow‟
• Auxins passes from shoot tip to the region of elongation and its
movement is basipetal (from apex towards base) in stem but
acropetal (from base towards apex) in roots.
• Auxin helps in elongation of both shoots and roots.
• Naturally occurring (endogenous) auxins in plants include indole-
3-acetic acid, 4- chloroindole-3-acetic acid, phenylacetic acid,
indole-3-butyric acid and indole-3-propionic acid.

7. • Charles Darwin and his son Francis performed experiments on
coleoptiles, and concluded the presence of a transmittable substance
that influences the growth of canary grass towards the light
• In 1913, Danish scientist Peter Boysen- Jensen demonstrated that the
signal was not transfixed but mobile.
• Went later proposed that the messenger substance is a growth-
promoting hormone, and named it as auxin. , It is asymmetrically
distributed in the bending region. Auxin is at a higher concentration
on the shaded side, promoting cell elongation, which results in
coleoptiles bending towards the light. Went concluded that “no
growth can occur without Auxin”

8. Physiological Role of Auxin
• Cell Elongation and longitudinal growth
• Apical Dominance
• Cell division
• root growth and root initiation
• Prevention of abscission
• Parthenocarpy
• Respiration
• Flower initiation
• Shortening of Internodes
• Plant growth Movements
• Fruit formation
• Wound response

9. • 2,4- D - Dichlorophenoxy Acetic acid
• IAA – Indole-3-Acetic Acid
• NAA- Naphthalene Acetic Acid
• IBA – Indole Butyric Acid
• NOA – Naphthoxy Acetic Acid
• 2,4,5-T – 2,4,5-Trichloroaphenoxy acetic acid

10. Role of Auxins in Plant Tissue culture
• Assist in initiating root development in stem cuttings
• Promote flowering
• Inhibit premature fruit and leaf shedding
• Enhance the natural abscission of old leaves and fruits or
flowers
• Assist cell division
• Balance and regulate xylem differentiation

11. Cytokinins
• The existence of growth factors that control plant cell division
was postulated by J. Wiesner in 1892.
• G. Haberlandt, in 1913 and 1921, described the existence of
putative substances that induced cell division.
• Folke Skoog and co-workers, at the University of Wisconsin,
investigated the nutritional requirements for growth of plant
tissue culture in the 1940s and early 1950s, and reported the
activity of specific cell division factors in vascular tissue.

12. • The investigations led Skoog, Miller and co-workers in 1955
to the isolation and identification of kinetin, a highly-active
cell division factor, from autoclaved herring sperm DNA.
• Letham in 1963 isolated a cytokinin, zeatin, from immature
corn kernels.
• A “kinetin-like” factor “zeatin” was isolated by Miller in 1961.
• Many phenylurea-derivatives have been shown to have
cytokinin-like activity.

13. Role of cytokinin
• Cell division, or cytokinesis, in plant roots and shoots
• Cell growth and differentiation
• Affects apical dominance,
• Promotes axillary bud growth
• Delays leaf senescence.
• Help to disrupt bud and seed dormancy
• Used to delay the aging of flowers and leaves

14. Commonly used Cytokinins
• Kinetin – 6-furfuryl amino purine
• BAP – benzyl amino purine
• BA- Benzyl Adenine
• Zeatin

15. Role of Cytokinin in Plant Tissue culture
• Used to instigate cell division in more mature tissues (Main
application of cytokinin in tissue culture)
• Stimulate lateral bud growth
• Promote cell division
• Help overcome apical dominance
• Stimulate lateral shoot growth
• Assist the plant in forming new, healthy leaves

16. GIBBERELLINS
• In 1926, Japanese scientist Eiichi Kurosawa identified that foolish
seedling disease was caused by the fungus Gibberella fujikuroi. Later
work at the University of Tokyo showed that a substance produced by
this fungus triggered the symptoms of foolish seedling disease and
they named this substance "gibberellin“.
• They are produced in the plant cell's plastids, or the double
membrane-bound organelles responsible for making food, and are
eventually transferred to the endoplasmic reticulum of the cell, where
they are modified and prepared for use.

17. Role of Gibberellin in plants
• Cell elongation,
• Help the plants to grow taller.
• They also play major roles in germination
• Elongation of the stem,
• Fruit ripening and
• Flowering

18. • Commonly used Gibberellins: GA3
• Use in Plant Tissue Culture:
• Breaking bud dormancy
• Stem Elongation

19. Abscisic Acid
• Abscisic acid is a sesquiterpene, which has important roles in
seed development and maturation, in the synthesis of proteins
and compatible osmolytes, which enable plants to tolerate
stresses due to environmental or biotic factors, and as a general
inhibitor of growth and metabolic activities.

20. Role in plants and in PTC
• Induces Seed and bud dormancy, the control of organ size and
stomatal closure.
• It is often used in tissue culture systems to promote somatic
embryogenesis and enhance somatic embryo quality by increasing
desiccation tolerance and preventing precocious germination.
• ABA is also employed to induce somatic embryos to enter a
quiescent state in plant tissue culture systems and during synthetic
seed research.

21. Ethylene
• Ethylene (gaseous hormone) is produced from essentially all parts
of higher plants, including leaves, stems, roots, flowers, fruits,
tubers, and seeds.
• Ethylene production is induced during germination, ripening of
fruits, abscission of leaves, and senescence of flowers.
• Play an important role in fruit ripening, induction of flowering, loss
of chlorophyll, abortion of plant parts, stem shortening, abscission
(dropping) of plant parts, epinasty (stems bend), and dormancy. It
can be produced when plants are injured, either mechanically or by
disease.