Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations

1. Table of Contents
Introduction.......................................................................................................................................2
ABSCISIC............................................................................................................................................2
Functions of abscisic hormone in plant.............................................................................................2
Agricultural uses of abscisic hormone ..............................................................................................3
Cytokinins..........................................................................................................................................3
Functions of abscisic hormone in plant.............................................................................................4
Uses of cytokinins inAgriculture and Horticulture.............................................................................4
AUXINS..............................................................................................................................................5
Functions of abscisic hormone in plant.............................................................................................5
Uses of Auxins in Agriculture and Horticulture..................................................................................6
Gibberellins........................................................................................................................................7
Functions of Gibberellins.................................................................................................................8
Agricultural Applications of Gibberellins...........................................................................................9
ETHYLENE ........................................................................................................................................10
Functions of Ethylene in plant........................................................................................................10
Agricultural application of Ethylene ...............................................................................................10
Conclusion .......................................................................................................................................11

2. Introduction
Plant hormones are signal molecules produced within the plant, and occur in extremely low
concentrations. Hormones regulate cellular processes in targeted cells locally and, moved to other
locations, in other functional parts of the plant. Hormones also determine the formation of flowers,
stems, leaves, the shedding of leaves, and the development and ripening of fruit. Plants, unlike
animals, lack glands that produce and secrete hormones. Instead, each cell is capable of producing
hormones. Plant hormones shape the plant, affecting seed growth, time of flowering, the sex of
flowers, senescence of leaves, and fruits. They affect which tissues grow upward and which grow
downward, leaf formation and stem growth, fruit development and ripening, plant longevity, and
even plant death. Hormones are vital to plant growth, and, lacking them, plants would be mostly a
mass of undifferentiated cells. So they are also known as growth factors or growth hormones
ABSCISIC
Abscisic acid is a single compound. It was called abscisic II originally because it was thought to
play a major role in abscission of fruits. It major role in bud dormancy. (Johnson, 2009)
Functions of abscisic hormone in plant
 Closing of stomata
Most the water taken up by a plant is lost in transpiration. Most of this leaves the plant through the pores
called stomata in the leaf. Each stoma is flanked by a pair of guard cells. When the guard cells are turgid,
the stoma is open. When turgor is lost, the stoma closes. In angiosperms and gymnosperms ABA is the
hormone that triggers closing of the stomata when soil water is insufficient to keep up with transpiration.
 Protecting cells from dehydration
ABA signalling turns on the expression of genes encoding proteins that protect cells in seeds as well as in
vegetative tissues from damage when they become dehydrated.
 Root growth
ABA can stimulate root growth in plants that need to increase their ability to extract water from the soil.
 Bud dormancy
ABA mediates the conversion of the apical meristem into a dormant bud. The newly developing leaves
growing above the meristem become converted into stiff bud scales that wrap the meristem closely and will
protect it from mechanical damage and drying out during the winter.

3.  Seed maturation and dormancy
Seeds are not only important agents of reproduction and dispersal, but they are also essential to the survival
of annual and biennial plants. These angiosperms die after flowering and seed formation is complete. ABA
is essential for seed maturation and also enforces a period of seed dormancy.
 Abscission
ABA also promotes abscission of leaves and fruits (in contrast to auxin, which inhibits abscission). It is, in
fact, this action that gave rise to the name abscisic acid. The dropping of leaves in the autumn is a vital
response to the onset of winter when ground water is frozen and thus cannot support transpiration and snow
load would threaten to break any branches still in leaf.
 Apical dominance
ABA moving up from the roots to the stem synergizes with auxin moving down from the apical meristem
to the stem in suppressing the development of lateral buds. The result is inhibition of branching or apical
dominance.
Agricultural uses of abscisic hormone
Abscisic Acid Application Enhances Drought Stress Tolerance in Bedding Plants.
Drought stress is a major cause of postproduction decline in bedding plants. The plant hormone
abscisic acid (ABA) regulates drought stress responses by mediating stomatal closure, thereby
reducing transpirational water loss.
Cytokinins
Cytokinins or CKs are a group of chemicals that influence cell division and shoot formation. They
are called kinins since after isolated from yeast cells. They also help delay senescence of tissues,
are responsible for mediating auxin transport throughout the plant, and affect internodal length and
leaf growth. They have a highly synergistic effect in concert with auxins, and the ratios of these
two groups of plant hormones affect most major growth periods during a plant's lifetime.
Cytokinins counter the apical dominance induced by auxins; they in conjunction with ethylene
promote abscission of leaves, flower parts, and fruits. (Tortora and, Derrickson, 2009)

4. Functions of abscisic hormone in plant
The correlation of auxins and cytokinins in the plants is a constant. Because cytokinin promotes
plant cell division and growth, produce farmers use it to increase crops.
The cytokinin stimulate growth, a hormone that promotes cytokinesis (cell division).Cytokinins
are most abundant in growing tissues, such as roots, embryos, and fruits, where cell division is
occurring.
Cytokinins are known to delay senescence in leaf tissues, promote mitosis, and stimulate
differentiation of the meristem in shoots and roots. Many effects on plant development are under
the influence of cytokinins,
Conjunction with auxin or another hormone. For example, apical dominance seems to result from
a balance between auxins that inhibit lateral buds and cytokinins that promote bushier growth.
Uses of cytokinins in Agriculture and Horticulture
Cytokinins have recently been found to play a role in plant pathogenesis. For example, cytokinins
have been described to induce resistance against Pseudomonas syringae in Arabidopsis thaliana.
Also in context of biological control of plant diseases cytokinins seem to have potential functions.
Production of cytokinins by Pseudomonas fluorescens G20-18 has been identified as a key
determinant to efficiently control the infection of A. thaliana with P. syringae
Plant hormones cytokinins regulate various aspects of plant growth and development. For their
positive effects on branching, delaying of senescence, nutrient remobilisation, flower and seed set
control they became interesting substances in search for potential agrochemicals.

5. AUXINS
Auxins are a family of hormones found in plants. Auxins are mostly made in the tips of the shoots and
roots, and can diffuse to other parts of the shoots or roots. They change the rate of elongation in plant cells,
controlling how long they become. Shoots and roots respond differently to high concentrations of auxins:
(Campbell, 2008)
Functions of abscisic hormone in plant
 Phototropism
In a shoot, the shaded side contains more auxin. This means that the shaded side grows longer, causing the
shoot to bend towards the light.
The diagram shows the typical results shown by oat seedlings grown in a box with a light from
one side
 Gravitropisms
Auxins are also involved in gravitropisms. In a root placed horizontally, the bottom side contains more
auxin than the top side. This makes the bottom side grow less than the top side, causing the root to bend in
the direction of the force of gravity.
In a shootplacedhorizontally, the bottom side contains more auxin than the top side. This makesthe bottom
side grow more than the top side, causing the shoot to bend and grow against the force of gravity.

6. Uses of Auxins in Agriculture and Horticulture
 Apical Dominance:
The auxins greatly influence the development of plant form and structure. It has long been known that
while the mainshootof a plantis growing,itslateral budsare inhibited.If,however,the budat the apex
is cut off, the lateral buds begin to develop.
 Meristematic Activity
Auxinaffectsthe meristematicactivityof cellsotherthanthose involvedintumorand callusproduction.
Auxinproducedinthe apical budstimulatesandregulatesthe activityof the cambiuminwoodyplants.It
seemsprobablethatthe resumptionof cambialgrowthinthe springisduetoauxinproducedbythe buds
in this season.
 Rooting
Propagation of plants by vegetative means is quite commonly practiced in horticulture. Several
experiments performed on a great variety of plants showed that auxin applications are generally
beneficial in bringing about the rooting of cuttings. It is extremely useful to the horticulturists, for by
meansof ita greatmany geneticallyidentical plantsmaybe made froma single individual,andadesired
genetic pattern
 Parthenocarpic or Seedless Fruits
Another property of auxins that has grown to economic importance is their ability, when applied to the
flowers of certain species, to initiate development of fruit without pollination.
 Prevention of Premature Fall of Fruits
In growersof citrus,applesandpearsuse large amountsof auxinsforthe preventionof premature fall of
fruits.
 Sex Expression
The spray of auxins increases the number of female flowers in cucurbits. In maize, application of
Nepthalene Acetic Acid during the period of inflorescence differen-tiation can induce formation of
hermaphrodite or female flowers in a male inflorescence. Thus auxins induce femaleness in plants.
 Control of Lodging

7. In some plants when the crop is ripe and there is heavy rain accompanied by strong winds, the plants
bendas a resultof whichthe ear (inflorescence) getssubmergedinwateranddecays.If a dilute solution
of any auxin is sprayed upon young plants, the possibility of bending of plants is reduced as the stem
becomes stronger by the application of auxins.
Gibberellins
include a large range of chemicals that are produced naturally within plants and by fungi. Chemical
produced by a fungus called Gibberella fujikuroi that produced abnormal growth in rice plants.
Gibberellins are important in seed germination, affecting enzyme production that mobilizes food
production used for growth of new cells. This is done by modulating chromosomal transcription.
In grain seeds, a layer of cells called the aleurone layer wraps around the endosperm tissue.
Absorption of water by the seed causes production of GA. The GA is transported to the aleurone
layer, which responds by producing enzymes that break down stored food reserves within the
endosperm, which are utilized by the growing seedling. GAs produce bolting of rosette-forming
plants, increasing internodal length. They promote flowering, cellular division, and in seeds
growth after germination. Gibberellins also reverse the inhibition of shoot growth and dormancy
induced by ABA. The gibberellins are weakly acidic phytohormones which help in longitudinal growth
of stem. (H.Edward, 2005)
Avena test (a) A piece of mica inserted on the shaded side prevented curvature of the coleoptile, (b) but not
when it was inserted on the illuminated side, (c) when the tip was removed (d) but was put back with a
block of gelatine, (e) normal phototropic curvature occured

8. Functions of Gibberellins
 Stem elongation
Gibberellins cause stem elongation and leaf expansion. It is believed that certain types of
dwarfness are due to gibberellins deficiency. But it has no effect on roots.
 Bolting
Gibberellins induce stem elongation in rosette plants. Cabbage is a rosette plant with profuse leaf
growth and retarded intermodal length. Just prior to flowering, internodes elongate enormously.
This is called bolting. Bolting needs either long days or cold nights. When a cabbage head is kept
under warm nights, it retains its rosette habit. Bolting can be induced artificially by the application
of gibberellins under normal conditions.
(Johnson, 2009)
 Seed Germination
Gibberellins promote seed germination in lettuce, cereals.
 Breaking of seed dormancy
Gibberellins break dormancy of buds and tubers. But in root tubers it inhibits the development of
the root tuber.

9.  Parthenocarpy
Gibberellins cause parthenocarpy in apple and pear.
 Increasing Fruit Size
Gibberellins along with auxin control the growth and development of fruits.
 Flowering and sex expression
Gibberellins control flowering in long day plants. Gibberellins promote the production of male
flowers, either in place of female flowers in monoecious plants or in genetically female plants such
as cucurbits.
Agricultural Applications of Gibberellins
 Fruit growth and parthenocarpy
Increased yield (larger size) and better shape of grapes is obtained by treating the fruit bunches
with GA. It induces parthenocarpy in apples, pears, tomatoes and cucumbers.
 Delayed ripening
Gibberellins delay fruit maturity and senescence in lemons, oranges and cherries. This helps in
storing the fruits. Used in long distance trade of fruits.
 Flowering
Gibberellins help in the flowering of many long day plants.
 Breaking of Dormancy
Gibberellins treatment helps in breaking dormancy in “seed potatoes” resulting in uniform crop
emergence.
 Malting
Gibberellins have been used to increase synthesis of various hydrolytic enzymes such as amylase,
ribonuclease and protease in aleurone cells of barley.

10. ETHYLENE
Ethylene is a plant hormone that differs from other plant hormones in being a gas. As they approach
maturity, many fruits (example. Apples, oranges, avocados) release ethylene. Ethylene then promotes the
ripening of the fruit. The presence of ethylene is detected by transmembrane receptors in the endoplasmic
reticulum (ER) of the cells. Binding of ethylene to these receptors unleashes a signalling cascade that leads
to activation of transcription factors and the turning on of gene transcription.
Functions of Ethylene in plant
 Ethylene affects fruit-ripening: Normally, when the seeds are mature, ethylene production
increases and builds-up within the fruit, resulting in a climacteric event just before seed
dispersal.
 Ethylene inhibits elongation of stem and roots and causes swelling of plant parts.
 Ethylene retards flowering in most plants but also increases flowering in some plants.
 Treatment of plants with ethylene increases the number of female flowers and fruits in
cucumber.
 Ethylene is considered as responsible for positive geotropic bending of roots.
 Ethylene inhibits the growth of lateral buds and thus causes apical dominance.
 Ethylene stimulates the growth of fruits in some plants. It is considered responsible for the
changes that occur during the ripening of fruits.
 Ethylene stimulates rooting of cuttings, initiation of lateral roots and growth of root hair.
 Ethylene promotes the yellowing and senescence of leaves. It also induces flower fading
in pollinated orchids. (Srivastava, 2002)
Agricultural application of Ethylene
The plant hormone ethylene promotes ripening, as seen in the ripening of dates. Ethylene is widely used in
agriculture. Commercial fruit growers control the timing of fruit ripening with application of the gas.
Horticulturalists inhibit leaf dropping in ornamental plants by removing ethylene from greenhouses using
fans and ventilation.

11. Conclusion
There exists a certain elegance by which the hormones counteract each other, regulate each other,
and create completely unique and unexpected effects in tandem.The balance of auxin and
cytokinin, not either hormone in isolation, allow for calluses to differentiate, while abscisic acid
and gibberelins struggle against each other in regulation of seed dormancy.
And, thanks to the ability of artificial synthesis and extraction processes, agricultural and
ornamental plant growth can be made to change to whatever needs mankind demands of it.In some
cases, as it is in abscisic acid, humanity can lay claim to having already synthesized a chemical
superior to what can be obtained in nature, prolonging the natural protective effect.
Those people can feed themselves, clothe themselves, and pull up their economic status through
agriculture far more easily, and perhaps, far more reliably, despite wind and cold.And for much of
the same reasons, big business will find profits lining their pockets like never yet, by making larger
operations ever more efficient, ever more yielding, ever less labour intensive, and ever more
diverse in its ability to use land.

12. References
Campbell,N.A.(2008). Biology . UnitedStatesof America:PearsonEducation.
Elliot,T.(1979). a brief introduction to plant biology. New York:Wiley.
H.Edward.(2005). The physiology of flowering plants. London: Cambridge UniversityPress.
Johnson,R.(2009). Biology . USA.
Srivastava,L.M. (2002). Plantgrowthand development. USA:AcademicPress.
The InternationalPlantGrowthSubstancesAssociation.(n.d.).Retrievedfrom
https://pages.wustl.edu/ipgsa/ethylene.
Tortora and, Derrickson.( 2009). Principlesof Anatomy and Physiology. Wiley:JohnWiley&Sons,Inc.