Presentation is about Hormones present in seeds and their role in growth and development of plants.

2. HORMONES IN DEVELOPING SEEDS :
COMPOSITION, LOCATION AND ROLES OF
SEED HORMONES

3. HORMONES
• Hormone- gr. to excite. Organic
substances produced natuirally in
small amounts that regulate and
coordinate metabolism, growth and
morphogenesis.
• Plant Hormones: Plant hormones
(also known as phytohormones) are
chemicals that regulate plant growth

4.  Leaf primordia, young leaves,
developing seeds.
 Polarly (unidirectionally) and
nonpolarly.
 Young tissues of the shoot and
developing seeds.
 Xylem and phloem.
 Root tips.
 From roots to shoots via xylem.
 Most tissues in response to
stress.
 Diffusion from site of synthesis.
 Mature leaves and roots, seeds.
 From leaves in phloem and from
the roots in the xylem.
PLANT
HORMONES

5. AUXINS
In 1881, CHARLES DARWIN and his son Francis performed
experiments on coleoptiles, the sheaths enclosing young
leaves in germinating grass seedlings.
First of the major hormones to be discovered.
The four naturally occurring (endogenous) auxins are IAA,
CIAA, Phenyl acetic acid and IBA; only these four were
found to be synthesized by plants.
Major Auxins is IAA.
On the molecular level, all auxins are compounds with an
aromatic ring and a carboxylic acid group.
Precursor for biosynthesis in seed tissues is TRYPTOPHAN
not derived from the parent plant.

6. 2,4-D
NAA
Dicamba
Picloram
2,4,5- Trichloro
phenoxy acetic
acid
IAA
4-CI-IAA
PAA
IBA

7. Found in free form and bound form.
IAA arabinoside
IAA myo-inositol
IAA myo-inositol arabinoside
Bound forms acts as precursors.
Both type of Auxins can be extracted from endosperm
(Maize & other cereals) and embryo (Peas and Dicots)
Free IAA content in Pea is typical that in developing seeds,
as its concentration rises to peak and then diminishes with
relatively low amount at maturity.
Variations occur as in Apple 2 peaks are observed.
First peak during change in endosperm from coenocytic to
cellular structure and second with formation of new
endosperm cells.
Final decline is due to metabolic conversion to bound forms
and other products.

8. ABA moves UP and DOWN
Auxins only down
Cytokinin only UP
GA both directions
Auxin Provides Chemical
Signals That Communicate
Information Over Long
Distances

9. Role of Auxins
Apical Dominance
Fruit Development
Differentiation and
Regeneration of Vascular
Tissue
Formation of Lateral and
Adventitious Roots

10. Prevents Abscission Herbicides Phototropism
Geotropism

11. Auxin produced by seeds promotes ovary
tissue growth

12. GIBBERLLINS
Gibberellins (GAs) are plant hormones that regulate growth and
influence various developmental processes.
Gibberellin was first recognized in 1926 by Japanese scientist, Eiichi
Kurosova, studying bakane, the "foolish seedling" disease in rice.
First isolated in 1935 by Teijiro Yabuta and Sumuki, from fungal
strains (Gibberella fujikuroi) provided by Kurosawa. Yabuta named
the isolate as “GIBBERELLIN”.
The bioactive GAs are GA1, GA3, GA4, and GA7.
They are produced in stem and root apical meristems, seed
embryos, and young leaves
Most bioactive GAs are located in actively growing organs on plants.
GAs are usually produced from the methylerythritol phosphate
(MEP) pathway in higher plants.

13. GGAA11 GGAA33

14. • Many GA conjugates have also been identified, such as
the polar, water soluble Glucopyranosides and
Glucopyranosyl esterase.
• GA synthesis in cell-free systems from immature seed of
Cucurbita maxima and P.sativum has following pathway
 Interconversion of GAs also observed in developing
seeds or in cell free embryo extracts.
2) GA12 GA15 GA24 GA9 GA51 GA51catabolite

15.  They are produced in stem and root apical
meristems, seed embryos, and young leaves.
 At early stages of seed development, the major
GAs are active and inactive ones are produced at
the end of seed maturity due to formation of
various conjugates and GA catabolites.
 Peak activity of endogenous GA found at 18-22
days due to combined effect of GA9 and GA20.
 GA distributed unequally in seed parts such as in
testa, cotyledons and axis in different
concentrations (Pea). In maize GA1 content in
embryo is 40 times higher than in endosperm.

17. Gibberellin Plays Multiple Roles in
1) Breaking Seed Dormancy
2) In Germination

18. 3) Gibberellin (GA) causes dwarf
mutants to grow tall.
4) Gibberellin causes hyper-elongation
of shoots by stimulating cell division
and elongation.
5) Gibberellin Can Cause Bolting
6) Gibberellin Affects
Fruit Development

19. CYTOKININS
• Cytokinins (CK) are a class of plant growth substances
that promote cell division, or cytokinesis, in plant roots
and shoots.
• Kinins are widely distributed in plants, especially in seed.
Kinins isolated from immature maize seed.
• They are produced in the roots and transported
throughout the plant via the xylem.
• They are involved primarily in cell growth and
differentiation, but also affect apical dominance, auxiliary
bud growth, and leaf senescence.
• There are two types of cytokinins:
1. Adenine-type represented by kinetin, zeatin, and BAM.
2. Phenylurea-type like Diphenylurea and Thidiazuron
(TDZ).

20. Derivatives of Cytokinins can be present
in glycosylated forms containing ribose,
Glucose or both sugars.
Amount of cytokinins increases during
seed development, particularly while
seed tissues are growing and then
declines at maturity.
Cytokinins regulates a range of plant
activities including seed germination.
They are active in all stages of
germination.
Also affect the activities of meristemic
cells in roots and shoots, as well as leaf
senescence. In addition, they are
effective in nodule formation

22. Adenosine phosphate-isopentenyl transferase (IPT)
catalyses the first reaction in the biosynthesis of
isoprene Cytokinins. It may use ATP, ADP, or AMP as
substrates and may use dimethyl allyl diphosphate
(DMAPP) or hydroxy methyl butenyl diphosphate
(HMBDP) as prenyl donors.
Cytokinins can also be produced by recycled tRNAs in
plants and bacteria.
Auxin is known to regulate the biosynthesis of
Cytokinins.
Recent years kinins have attracted the attention
since they participate in the biosynthesis of proteins,
chlorophyll and other vital important compounds.

23. Role of Cytokinins
Promote Cell Division Delay Leaf Senescence
Promote the Growth of Lateral Buds
Cytokinins are also able to enhance
seed germination by the alleviation of
stresses such as salinity, drought, heavy
metals and oxidative stress. They can be
inactivated by the enzyme cytokinin oxidase/
dehydrogenase catalyzing the cleavage of their
unsaturated bond. (Galuszka et al.,2001 )
Cytokinins are also able to enhance
seed germination by the alleviation of
stresses such as salinity, drought, heavy
metals and oxidative stress. They can be
inactivated by the enzyme cytokinin oxidase/
dehydrogenase catalyzing the cleavage of their
unsaturated bond. (Galuszka et al.,2001 )

24. Somatic embryos formation
Cytokinins encourage the growth of lateral
shoots.
Cytokinins encourage the growth of lateral
shoots.

25. ABSCISIC ACID (ABA)
Abscisic acid (ABA), also known as abscisin II and dormin.
ABA functions in many plant developmental processes,
including bud dormancy
Abscisic acid is a growth-inhibiting hormone largely
responsible for seed dormancy.
ABA can be isolated from immature seeds of many
species.
Free from of inhibitor can occur at relatively high
concentrations especially in legumes.
Bound forms like Glucosyl ester and glucoside are also
common.

26. Both free and bound forms can be
located in various parts of seed like
embryo, endosperm and the enclosing
tissues.
ABA is an isoprenoid, which is
synthesized in the plastidal 2-C-methyl-
D-erythritol-4-phosphate
(MEP) pathway;
ABA rises in its concentration during
seed development, reaches one or
two peaks and generally then declines
rapidly at the time of drying.

27. Location and timing of ABA biosynthesis
1. Released during desiccation of the vegetative tissues
and when roots encounter soil compaction.
2. Synthesized in green fruits at the beginning of the
winter period.
3. Synthesized in maturing seeds, establishing dormancy
4. Mobile within the leaf and can be rapidly translocated
from the roots to the leaves by the transpiration stream
in the xylem.
5. Produced in response to environmental stress, such as
heat stress, water stress and salt stress.
6. Synthesized in all plant parts, e.g., roots, flowers, leaves
and stems

28. Role of ABA
1) It inhibits precocious germination and viviparity.
2) Adversely affects the process of seed germination.
For ex: Conc. of 1–10 μM can inhibit seed germination in
plants like Arabidopsis thaliana. However, other hormones
including GA, ethylene, cytokinins, and brassinosteroids, as
well as their negative interaction with ABA, can positively
regulate the process of germination. (Kucera et al., 2005;
Muller et al.,2006)
3) Promotes seed storage reserve accumulation and
descication tolerance.
4) Promotes maturation and dormancy.
5) When seed has highest ABA level, seed acumulates storage
compounds that will support seedling growth and
germination subsequently.
6) Synthesis of storage proteins, lipids and LEA proteins.

29. 7) Antitranspirant - Induces stomata closure, decreasing
transpiration to prevent water loss.
8) Down regulates enzymes needed for photosynthesis.
9) Acts on endodermis to prevent growth of roots when
exposed to salty conditions
Role as a Root-to-
Shoot Signal Viviparity Stomatal Closure

30. ETHYLENE
Ethylene is also an important natural plant hormone,
used in agriculture to force the ripening of fruits.
It is a hydrocarbon with the formula C2H4 or
H2C=CH2.
It acts at trace levels throughout the life of the plant
by stimulating or regulating the ripening of fruit, the
opening of flowers, and the abscission (or shedding)
of leaves.

31. Ethylene biosynthesis in
plants
Ethylene is produced from essentially all parts of higher
plants, including leaves, stems, roots, flowers, fruits,
tubers, and seeds; regulated by various developmental
and environmental factors.
Its production is induced during certain stages of growth
such as germination, ripening of fruits, abscission of
leaves, and senescence of flowers.
Its production can also be induced by a variety of external
aspects such as mechanical wounding, environmental
stresses, and certain chemicals including auxin and other
regulators.

32. Ethylene is biosynthesized from the amino acid
methionine to S-adenosyl-L-methionine (SAM, also
called Adomet) by the enzyme Met Adenosyl
transferase.
SAM is then converted to Alpha amino
cyclopropene-1-carboxylic acid (ACC) by the enzyme
ACC synthase (ACS).
The final step involves the action of the enzyme ACC-oxidase
(ACO), formerly known as the ethylene
forming enzyme (EFE).
Induced by endogenous or exogenous.
ACC synthesis increases with high levels of auxins,
especially IAA and cytokinins.

33. 1. Seed Germination : The amount of ethylene increases during the
germination of many plant seeds including wheat, corn, soybean
and rice, affecting the rate of seed germination (Pennazio and
Roggero, 1991; Zapata et al., 2004). ACC can enhance seed radicle
emergence through the production of ethylene, produced in the
radicle.
2. Inhibits the adverse effects of ABA and releases seed dormancy.
3. Breaks bud dormancy in Potato tubers.
4. Thickening and shortening of hypocotyls with pronounced apical
hook.
5. Induces root hair growth — increasing the efficiency of water and
mineral absorption.
6. Sex expression in monoecious species (ratio of ♀ to ♂)
7. Thigmomorphogenesis (reduced stem elongation in some
environments)
Role of Ethylene

34. Fruit Ripening Thigmomorphism

35. POSSIBLE ROLE OF SEED HORMONES
Endogenous GR play important roles in the
regulation of certain aspects of seed
1.Seed growth and Development
2.Germination and Growth
3.Fruit growth and development
4.Other effects of seed hormones.

36. Seed growth and Development
Most of the studies shown that GR with seed development
comes from correlations between regulator content and
embryo growth.
In case of dwarf pea seeds highest concentration of GA (GA9
& GA20) occur during maximum growth of developing embryo.
GA deficient mutants of Pea Mutants show seed abortion
where as no effect observed in mutants of Arabidopsis and
tomato.
During cell division and enlargement highest concentration of
Cytokinins are observed.
CK in liquid endosperm participate in the mobilization of
assimilates.
ABA associated with arrest of embryo growth. In case of
Barley and rapeseed normal embryo development can occur
but germination and growth cannot.

37. ABA content higher in young, non-germinable seeds
than older ones. (Several cereals & Legumes)
Suppression of pre-mature germination.
Ex: Most viviparous mutants of Maize have 20-25% of
ABA conc. Than normal wild non-viviparous type.
Relative insensitivity to ABA found in Mangroves where
vivipary is common occurance.
Involved in regulation of storage protein synthesis.
(Soybean & P.vulgaris)
Involved in accumulation of sugars enhancement in
Grapes and grain filling in Wheat.
Arabidopsis mutants shown reduced concentration of
certain storage proteins and TAG. But this is not found
in Tomato mutants.

38. Germination and Growth
Auxin by itself is not a necessary hormone for seed
germination. However, according to the analyses
regarding the expression of auxin related genes, auxin is
present in the seed radicle tip during and after seed
germination.
The growth and development of different plant parts,
including the embryo, leaf and root is believed to be
controlled by auxin transport. (Popko, J. Et al.,2010)
ABA/GA ratio affects embryo dormancy. Dormancy occur
when ABA sensitivity is higher than GA sensitivity.
Seed germination occurs at low ABA/GA ratio.
ABA control embryo dormancy and GA controls embryo
germination.

39. ABA affects testa or seed coat growth characteristics
such as thickness and affects the GA-mediated embryo
growth potential.
Endosperm is composed of living tissue that actively
responds to hormones generated by embryo. Endosperm
often acts as barrier for seed germination.
Living cells respond to and also affect ABA/GA ratio and
mediate cellular sensitivity; GA thus increases the
embryo growth potential and weakens endosperm.
GA and Cytokinins broke seed dormancy of certain light
sensitive seeds such as lettuce and tobacco.
GA involved in α-Amylase synthesis in aleuronic layer.
GA stimulates germination in pine, grape, mustard,
cabbage etc.,

40. Cytokinins affect the activities of meristematic
cells in roots and shoots.
Cytokinins are also able to enhance seed
germination by the alleviation of stresses such
as salinity, drought, heavy metals and oxidative
stress. (Peleg, Z., Blumwald, E. 2011)
Inhibitory effect of far red light treatment on
germination is overcome by Kinetin treatment.
Parasitic weed Striga germination can be
induced by treating with Cytokinins even in
absence of host.

41. Fruit Growth and Development
Fruit set and pod elongation in pea are normally
dependent on the presence of seeds. Developing seeds
produce signal molecules that regulate cell division and
expansion of surrounding fruit tissues.
Interaction between GA and Auxin present in seeds and
pericarps of pea are responsible for cell division and
expansion in developing fruits of pea.
Growth of fresh fruits is linked to the activity of the
developing seed. Eg: Fruit size in cucurbits positively
correlated to seed number.
Auxin in developing seeds promotes flesh growth in
strawberry. In deseeded strawberry auxin application
restores flesh growth.

43. Other Effects
Treatment of pea seedlings with NAA or GA
prevents formation of abscission layer.
Abscission of fruits and leaves promoted by ABA
from developing seeds.
Apple seeds rich in GA and can cause flower bud
suppression.

45. • The high level of auxin present during all the seed development
phases suggests that this hormone has a key role throughout the
entire program of seed formation.
• The pattern of CK accumulation is the opposite with respect to
auxin. CKs have a prominent role during the phase that involves cell
divisions, decreasing progressively during the maturation phase,
when cell expansion prevails.
• The BR follow the same pattern of CKs. The highest concentration
of BRs is found at the beginning of seed development, and is
detected in the maternally derived tissues (i.e., integuments). Their
levels decrease at the end of maturation.
• The pattern of accumulation of GA is characteristic, showing two
peaks corresponding to specific phases of seed development: the
stage of embryo differentiation, when the GAs promote cell growth
and expansion, and the end of the maturation phase.
• ABA shows an accumulation pattern complementary to the GAs,
being the main hormone that inhibits all the processes induced by
GAs.

46. Additional Chemical Signals
• Brassinosteroids- required for normal growth of
most plant tissue. BRs are plant steroid hormones
involved in several developmental programs,
including seed development.
• They function in the pathway that regulates ovule
number and seed size and shape, in some cases
complementing CKs and auxins.
• They also participate in the regulation of seed
germination, by antagonizing the inhibitor effect
of ABA (Zhang et al., 2009), and being synergic to
gibberellins (Leubner-Metzger, 2001).

47. • Salicylic acid- signal in defense responses to
plant pathogens.
• Jasmonates- plant growth regulation and
defense.
• Polyamines- growth and development;
mitosis and meiosis.
• Systemin- long-distance signal that activates
chemical defenses against herbivores.
• Nitric oxide- signal in hormonal and defense
responses.

48. 11/26/14 Dept. of GPB 48

49. REFERENCES
1. Plant hormones and seed germination
Mohammad Miransari, D.L. Smith “Environmental and
Experimental Botany” 99 (2014) 110–121.
2. Seeds : Physiology of Development and Germination.
J.Derek Bewely and Michael Black. Second edition, Plenum
Publishers.
3. http://en.wikipedia.org/wiki/Plant_hormone.
4. Current perspectives on the hormonal control of seed
development in Arabidopsis and maize: a focus on auxin.
Antonella Locascio, Irma Roig-Villanova, Jamila Bernardi and
Serena Varotto. Frontiers in Plant Science Plant Evolution
and Development August 2014, Volume 5, Article 412.