plant growth inhibitors

1. PLANT HORMONE
(ABSCISIC ACID & ETHYLENE)
BY
A.MANOJ KUMAR (A9PBTOO4)
II M. Sc (BIO-TECHNOLOGY)

2. PLANT HORMONE:-
Definition:-
”’Plant hormones (or plant growth
regulators, or PGRs) are internally-secreted
chemicals in plants that are used for regulating
the plants growth.
According to a standard definition,
plant hormones are signal molecules produced
at specific locations, occur in low
concentrations, and cause altered processes in
target cells at other locations.
Growth in plants is regulated by a
variety of plant hormones, including auxins,
gibberellins, cytokinins, and growth inhibitors,
primarily abscisic acid and ethylene

3. Growth inhibitors
Growth inhibitors of various types have been
identified in plants.
The best characterized one is abscisic acid,
which is chemically related to the cytokinins.
It is probably universally distributed in higher
plants and has a variety of actions
Another growth inhibitor is ethylene, which is
a natural product of plants, formed possibly from
linolenic acid (a fatty acid) or from methionine (an
amino acid).

4. 1. ABSCISIC ACID
It is also called stress hormone because the
production of hormone is stimulated by drought,
water logging and other adverse environmental
conditions.
Abscisic acid is known as dormin as it induces
dormancy in buds, underground stems and seeds.
Its other names are abscissin II and inhibitor
B.
Abscisic acid is a mildly acidic dextrorotatory
cis sesquiterpene growth hormone which functions as
a general growth inhibitor by counteracting other
hormones (auxin, gibberellins, and cytokinins)
Functions of Abscisic Acid:
1. Bud Dormancy:
Abscisic acid induces dormancy of buds towards the
approach of winter.

5. 2. Seed Dormancy:
It is mainly caused by abscisic acid. Dormancy allows
seeds to tolerate desiccation and extremes of
temperature better. The buds as well as seeds sprout only
when abscisic acid is overcome by gibberellins. Because
of its action in inducing dormancy, abscisic acid or ABA is
also named as dormin.
3. Stoppage of Cambium Activity:
Formation of abscisic acid stops mitosis in vascular
cambium towards the approach of winter.
4. Abscission:
Abscisic acid promotes abscission of flowers and fruits.
5. Leaf Senescence:
Its excessive presence stops protein and RNA synthesis in
the leaves and hence stimulates their senescence (leaf fall
is actually promoted by ethylene).

6. BUD DORMANCYBUD DORMANCY CAMBIUM
LEAF ABSCISSION

7. 6.Transpiration
During desiccation and other stresses, abscisic acid is
rapidly synthesised. The inhibitor causes closure of
stomata and hence prevents transpiration.
7. Resistance:
Abscisic acid increases resistance of plants to cold and
other types of stresses. It is, therefore, also known as
stress hormone.
8.Starch Hydrolysis
Abscisic acid inhibits gibberellin mediated amylase
formation during germination of cereal grains.
9. Flowering:
In small quantities, abscisic acid is known to promote
flowering in some short day plants, e.g., Strawberry,
Black Currant.
10. Parthenocarpy:
ABA has been found to induce parthenocarpic
development in Rose.

8. FLOWERING

9. 2.Ethylene:
It is a gaseous hormone which stimulates
transverse or isodiametric growth but retards
the longitudinal one.
• Businessmen dealing with storing and
shipping of fruits had known quite early that a
rotten or ripe fruit could trigger early ripening
of other fruits present nearby.
• Cousins (1910) found that ripe oranges
produced a volatile substance that hastened
ripening of unripe bananas nearby.

10. Functions of Ethylene:
1. Growth:
Ethylene inhibits longitudinal growth but stimulates
transverse or horizontal growth and swelling of axis.
2. Gravity:
It decreases the sensitivity to gravity. Roots become Apo-
geotropic while stems turn positively geotropic. Leaves and
flowers undergo drooping. The phenomenon is called
epinasty. Seedlings develop tight epicotyl hook.
3. Senescence:
It hastens the senescence of leaves and flowers.
4. Abscission:
Abscission of various parts (leaves, flowers, fruits) is
stimulated by ethylene which induces the formation of
hydrolases.
5. Apical Dominance:
Ethylene promotes apical dominance and prolongs
dormancy of lateral buds.

11. 6. Breaking of Dormancy:
It breaks the dormancy of buds, seeds and storage
organs.
7. Abscisic Acid:
It seems that formation of abscisic acid in the leaves
under conditions of water stress is mediated through
ethylene.
8. Growth of Rice Seedling:
Ethylene promotes rapid elongation of leaf bases and
internodes in deep water rice plants. As a result leaves
remain above water.
9. Root Initiation:
In low concentration ethylene helps in root initiation,
growth of lateral roots and root hairs. This increases
the absorption surface of the plant roots.

12. BREAKING OF DORMANCY
GROWTH OF RICE SEEDLING

13. 10. Fruit Ripening:
It aids in ripening of climacteric fruits and dehiscence of dry
fruits. Climacteric fruits are fleshy fruits which show a
sudden sharp rise of respiration rate at the time of ripening
(respiratory climacteric). They are usually transported in
green or unripe stage. Ethylene is used to induce artificial
ripening of these fruits, e.g., Apple, Mango, Banana, etc.
11. Flowering:
It stimulates flowering in Pineapple and related plants as
well as mango though in other cases the gaseous hormone
causes fading of flowers. This helps in synchronizing fruit
set.
12. Sex Expression:
Like auxins and cytokinins, ethylene has a feminizing effect
on sex expression. The genetically male plants of Cannabis
can be induced to produce female flowers in the presence of
ethylene. The number of female flowers and hence fruit is
enhanced in monoecious plants like Cucumber.

14. DELAY OF FRUIT RIPENING

15. THANK YOU...