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Economic Importance of Plant Growth Regulators

Table of Contents

Introductionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip2

Plant growth regulatorhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip3

Auxin and it economic importancehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip3-6

Gibberellins and its economic importancehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip6-8

Cytokinins and its economic importancehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip8-9

Abscissic Acid and its economic importancehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip10

Ethylene and its economic importancehelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip10-11

Other hormoneshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip12

Conclusionhelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip13

Referenceshelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphelliphellip14

Introduction

According to Devlin and Witham (1986) ldquoplant growth regulators are organic

compounds other than nutrients that in small amounts promote inhibit or otherwise modify a

physiological process in plants Plant hormones or phytohormones are regulators produced by

plants in which a low concentration regulates plant physiological processesrdquo (p 354) The

growth regulators can either be natural or synthetic and are widely being used in the agricultural

production and even for economic importance

The plant growth regulators have various economic importances in agricultural field

Their importance has been boon and advantages for farmers and horticulturists They took

advantage to earn by the practical implication and implication of these hormones and growth

regulators The very assignment mainly comprises of economic importance of plant growth

regulators

The plant growth regulators primarily include auxin gibberellin cytokinin

ethylene and abscisic acid (ABA) Secondarily it also includes florigens anthesin

vernalin morphactins etc Each growth regulators have various role and functions

which contributes to economic of the farmers and horticulturists worldwide

This assignment basically contains economic importance of each growth

regulator with different uses and practical application in agriculture and horticulture

For example auxins are used to increase fruit-sets control flowering etc Gibberellins

is used to increase sugar content in sugarcane etc Similarly every hormone posses different role

and economic importance where this very assignment mainly discusses as below

Plant growth regulators Plant hormones Phytohormones

Plant hormones and growth regulators are chemicals that affect flowering aging root

growth distortion and killing of leaves stems and other parts prevention or promotion of stem

elongation etc

Rastogi (2011) defined that the plant growth regulator or phytohormone as an organic

substance produced naturally in plants controlling growth and other functions at a site remote

from its place of production in minute quantities Philips as cited in Pandey and Sinha (2006)

defined growth hormones as substances which are synthesized and transferred to other cells

where in extremely small quantities influence the developmental processes The growth

regulators can either be growth promoters or inhibitors A plant growth regulator is also an

organic compound either natural or synthetic that modifies or controls one or more specific

physiological processes within a plant through translocation And they can be either synthetic or

natural The growth regulators include

1 Auxins

2 Gibberellins

3 Cytokinins

4 Ethylene

5 Abscisic acid

6 Flowering hormones

7 Florigen Anthesins Vernalin Morphactinsetc

But major plant growth regulators are first five ones and are discussed as follows

1 Auxins

It is the plant growth regulators that mainly help in rooting besides its minor functions

This growth substance was found out by Charles Darwin in his book called The Power of

Movement of Plants He demonstrated that apical tips of seedlings are sensitive to unilateral

illumination and positive phototropism He concluded that the tip senses the unilateral light

stimulus but the curvature occurs down as a result of more rapid growth on the shaded than

illuminated side of the coleoptiles And he also noted that when the tip of coleoptiles was excised

no curvature response occurred Therefore he said that when seedlings are freely exposed to

lateral light some influence is transmitted from the upper to lower part causing the later bent

Similar observations were made by Boysen-Jensen (1913) and Went (1928) They too did

and demonstrated on coleoptiles

Characteristics

1 Polar translocation- movement from apex to downward

2 Apical bud dominance

3 Variable behavior root and shoot growth

4 Root initiation

5 Belay in abscission

There are many different natural and synthetic auxins with different functions

1 Indole acetic acid-IAA

2 Indolebutyrib acid=IBA

3 Napthalene acetic acid-NAA

4 24-dichlorophenoxy acetic acid-24-D

Role of Auxin

The following are some of the responses that auxin is known to cause as cited by Davies 1995

Mauseth 1991 Raven 1992 Salisbury and Ross 1992

Stimulates cell elongation

Stimulates cell division in the cambium and in combination with cytokinins in tissue

culture

Stimulates differentiation of phloem and xylem

Stimulates root initiation on stem cuttings and lateral root development in tissue culture

Mediates the tropistic response of bending in response to gravity and light

The auxin supply from the apical bud suppresses growth of lateral buds

Can induce fruit setting and growth in some plants

Delays fruit ripening

Promotes flowering

Stimulates growth of flower parts

Promotes femaleness in dioecious flowers

Stimulates the production of ethylene at high concentrations

Practical Application and its economic importance

1 Germination IAA IBA NPA 2 4-D are widely used to soak seeds for

germinationAuxins are widely used to break the dormancy of the seeds The pre-

treatment of seeds before sowing with IAA IBA 2 4-D etc found to have increased the

length of the hypocotyls at low concentration and shortening at higher concentration

Bhardwaj and Rao as cited in Pandey and Sinha (2006) reported that the effect of 24-D

on the growth and maturity of wheat and recorded 33 increased at 10 ppm treatment

Auxins can have very effective effects at very low concentration The higher concentration

and prolonged treatment retard and reduce germination

2 Rooting NAA and IBA are used for inducing the rooting of cuttings of woody plants

Malik and Chhonker as cited in Pandey and Sinha (2006) studied that the rooting effects

of different auxins and found out that the treatment of IBA and IAA are more superiors as

compared to other auxin type The effect of auxin NAA on mango varieties too has the

importance as a 10 induces 100 rooting

3 Flowering Hitchcock and Zimnermann as cited in Pandey and Sinha (2006) showed that

the even a minute quantity of auxins accelerated the flowering It is also reported that

IAA promotes the formation female flowers The application of auxins also helps to

increase the yield and flowering of wheat Das and Singh (1958) also studied the effect of

auxin IAA on flowering and fruiting in pineapple NAA and 2 4-D to induce flowering

in litchi and pineapple

4 ParthenocarpyIt is produced mainly by NAA and IBA Treatment of NAA in cucumber

and melon fruits produce seedless fruits (Das 1962)

5 Weeds controlThey are selective weeds killers and considerably used in the destruction

of weds in crop fields rail-roads lawns and forests Common weedicides of auxin in

nature includes 2 4-D and 2 4 5-T etc

In Agriculture and Horticulture

Auxins are used for

1 Propagation of plants by hormone treatment in cuttings scions

2 Prevention of pre-harvest drop of fruits

3 Increasing parthenocarpy

4 Increasing fruit-sets

5 Inhibition of prolonged dormancy

6 Control of flowering

7 Defoliation of plants

8 Prevention of leaf falls or abscission

9 Selective weed killers

2 Gibberellins

It is the second major plant hormones which is mainly functional for shoot proliferation

besides flowering and breaking of seed dormancy It was first known by a Japneses farmer

Konishi (1898) and working was found out by Kurosawa in 1926 He discovered as GA It was

first extracted from the ascomycetous fungus GibberellaFujikuroi the casual organisms of

ldquofoolish seedling of ricerdquo or commonly called bakanae of rice The infected plants were taller

seedless and pale in colour These symptoms were produced due the substances secreted by the

fungus

It is mainly of gibberrelinGA3 or A3

Characteristics

1 Prevention of genetic and physiological dwarfism

2 Breaking of dormancy

3 Induction of flowering long day plants

4 Increase amylase activity and

5 Substitute for chilling effects

Role of gibberellins

The following are the roles and functions of gibberellins as cited by Davies 1995 Mauseth

1991 Raven 1992 Salisbury and Ross 1992

Stimulate stem elongation by stimulating cell division and elongation

Stimulates boltingflowering in response to long days

Breaks seed dormancy in some plants which require stratification or light to induce

germination

Stimulates enzyme production -amylase in germinating cereal grains for mobilization of

seed reserves

Induces maleness in dioecious flowers (sex expression)

Can cause parthenocarpic fruit development

Can delay senescence in leaves and citrus fruits

1 Germination It has been widely used for germination experiments GA is found to

increase the length of hypocotyls and cotyledonary leaf (Chakravarti 1958) GA also has

important role in seed germination of cereals

2 Rooting Various experiments have suggested that the gibberellins have effect on

rooting Kato (1958) reported that it not only root initiation is inhibited but also the

stimulation of rooting by the auxin is also counteracted

3 Flowering GA induces flowering in long day plants and in plants requiring inductive

cold period It also promotes the formation of male flowers as it plays important role in

development of male flower

4 Parthenocarpy Mukerje and Dutta as cited in Pandey and Sinha (2006) have found out

that GA induces the formation of parthenocarpic fruits in brinjal It can also be done in

guava to produce parthenocarpic fruits It is also used to induce the parthenocarpy in

pome fruits and use to increase the fruit size and bunch length in grapes as well

5 Fruit Setting GA affects more positively on fruit setting Randhaw and Singh (1959)

observed an increase in fruit setting in seedless grapes an increased in fruit size fruit set

total yield and quality in sweet lime have also been due to the treatment of GA

GAs is used to increase the size of Thompson grapes berries It is used by some breweries to

increase the rate of malting by increasing the potential of starch digestion Gibberellins are also

use to increase sugar cane growth and sugar yields

It posses great uses in increasing stalk length and production breaking of dormancy

inducing uniform crop emergence producing staminate flowers loosening of fruit clusters

increasing the fruit size quickening of maturity improving fruit quality controlling cracking of

fruits reducing non-productive period promoting vegetative growth and flower size increasing

sugar content in sugar cane inducing flowering and so on

3 Cytokinins

Skoog (1964) noted that in general ldquothe term Cytokinin is universally used for substance

which promotes cell division and exerts other growth regulatory functions as kinetinrdquo It also

promotes cell division and influence cell differentiation and aging of leaves

Characteristics

1 Initiation of cell division

2 Delay of senescence

3 Use of tissue culture

4 Counteract apical dominance

5 Induces flowering short day plants

Role of Cytokinins

Stimulates cell division

Stimulates morphogenesis -shoot initiationbud formation in tissue culture

Stimulates the growth of lateral buds-release of apical dominance

Stimulates leaf expansion resulting from cell enlargement

May enhance stomata opening in some species

1 Cell division Braun and Wood (1962) demonstrated that on exogenous supply of

cytokinin a normal Vinca cell converts to a turmour cell Skoog also showed that IAA

alone produces few mitoses in tobacco pith tissue but kinetinin combination with IAA

induces more mitoses This hormone never acts alone but in association or combination

with hormones like auxins cytokinins etc

2 Cell enlargement Scot and Liverman as cited in Pandey and Sinha (2006) reported the

property of cell enlargement in the disc of etiolated leaf by cytokinin Similar results

were also made in tobacco pith and cortical cells of tobacco roots

3 Dormancy It ahs been found quite effective in breaking the dormancy of the seeds and

other plant organ

4 Apical dominance Wickson and Thimann (1958) found that this hormone counteract

the usual apical dominace of bud These hormones have also been reported to induce the

lateral bud formation which is apparently related to the vascular tissue differentiation

The major use for cytokinins derives from its ability to delay senescence and maintain

greenness The artificial highly active cytokinin benzyladenine is the main compound used

The treatment of holly for festive decorations enables its harvest many weeks prior to use Post-

harvest sprays are now available to prolong the storage life of green vegetables such as

asparagus broccoli and celery

These hormones also have used to increase shelf life of fruits quickening of root induction

and production of efficient root system It is also used to increase the yield and oil contents in

ground nuts to break the dormancy delay senescence causes cell division and so on

4 Abscissic Acid( ABA)

It is regarded as one of the principal accelerators of abscission and also bud dormancy It is

natural growth inhibitors and acts as a stress hormone that helps to cope with adverse

environmental conditions

Role of Abscissic Acid

A list of some of the known physiological effects caused by cytokinins is listed below

(Davies 1995 Mauseth 1991 Raven 1992 Salisbury and Ross 1992)

Stimulates the closure of stomata-water stress brings about an increase in ABA synthesis

Inhibits shoot growth but will not have as much affect on roots or may even promote

growth of roots

Induces seeds to synthesize storage proteins

Inhibits the affect of gibberellins on stimulating

Has some effect on induction and maintenance of dormancy

Induces gene transcription especially for proteinase inhibitors in response to wounding

which may explain an apparent role in pathogen defense

5 Ethylene

The only ripening hormone Denny as cited in Pandey and Sinha (2006) reported that

ethylene is highly effective in fruits ripening It is actually the natural product of ripening fruits

It is a gas at temperature under which a plant can survive It is a powerful inhibitor of root and

stem elongation

Role of Ehtylene

Ethylene is known to affect the following plant processes (Davies 1995 Mauseth 1991

Raven 1992 Salisbury and Ross 1992)

Stimulates the release of dormancy

Stimulates shoot and root growth and differentiation (triple response)

May have a role in adventitious root formation

Stimulates leaf and fruit abscission

Stimulates Bromiliad flower induction

Induction of femaleness in dioecious flowers

Stimulates flower opening

Stimulates flower and leaf senescence

Stimulates fruit ripening

Ethylene gas a wide variety of uses but its gaseous nature precludes its applications in

non-enclosed spaces Ethylene itself can be used to enhance the ripening of fruits such as

bananas in storage following their shipment in an unripe condition An ethylene-producing liquid

chemical 2-chloroethylphosphonic acid - commercially called Ethrel or Ethephon has been

introduced and it is sprayed onto the plant at a slightly acid pH When it enters the cells and

encounters the cytoplasm at about neutral pH it breaks down to release gaseous ethylene which

is commercially used for fruit ripening These hormones have a potential area of use in a wide

variety of fruits such as grapes cherries and citrus Promotion of female flower production in

cucurbits -cucumber squash and melon so as to increase the number of fruits produced per

plant It is also used for the promotion of flower initiation and controlled ripening in pineapples

Other hormones

1 Florigen These hormones are synthesized in the older leaves and then transferred

to the growing region where it initiates the floral and bud initiation It is mainly

responsible for flowering in plants It also called flowering hormones

2 Anthesins Its newly discovered hormones responsible for flower formation

which horticulturists use to induce the early flowering in some plants

3 Vernalin It is used to undergo and bring nervalisation in some plants

4 Morphactins They are synthetic growth regulators which have the various roles

and functions as natural growth regulators It has been effective in flowering

stimulation sequence of flowering position and number of flowers formation of

flowers inflorescence parthenocarpy etc

Conclusion

The plant growth regulators either synthetic or natural have been found great and wide

applications in agriculture and horticulture These growth regulators which in minute quantity

can have adverse effects to promote and modify a physiological process in plants On the

evidences of their adverse effects in small quantity these growth regulators have been found

greater applications and economic importance for farmers and horticulturists

The growth regulators are used to increase the fruit sizes to induce early flowering and

increase the number of flowering to break the dormancy of some seeds to quicken the maturity

and improve the fruit quality to increase the sugar content in sugarcane to increase the yield and

oil contents to promote the flower initiation and control ripening some other fruits and many

more Beside their major roles there are many other minor roles as sequence of flowering

position and number of flowers formation of flowers parthenocarpy root and shoot initiation

The knowledge of these growth regulators have been advantages and boon to many

agriculturists and horticulturists globally Similarly we too can take advantages of their roles and

applications so as to make livelihood living and earn money some amount out of it Besides the

availability of these hormones in our places we too can go for it with the loaned investment

which is highly economic

In nutshell I would say that the plant growth regulators either synthetic or natural have

wide applications and uses for economical purposes and livelihood as well For it has been

found too crucial and economical to take the advantage of knowledge of the roles and

applications of growth regulators Theses growth regulators have been used widely in many other

countries unlike ours due to lack of access to the facilities

Therefore I request everyone to take advantage of its roles and applications and work for

economic purpose and livelihood Let us make use of those growth regulators

References

Devlin RM amp Witham FH (1986) Plant Physiology (1st ed) Delhi CBS PUBLISHERS amp

DISTRIBUTORS

Nature of auxins (nd) Retrieved on 21st September 2011 from

httpwwwplant-

hormonesinfoauxinshtm

Nature of abscisicacid (nd ) Retrieved on 21st September 2011 from

httpwwwplant- hormonesinfoabscisicacidhtm

Nature of cytokinins (nd) Retrieved on 21st September 2011from

httpwwwplant-hormonesinfocytokininshtm

Nature of ethylene (nd) Retrieved on 21st September 2011from

httpwwwplant-hormonesinfoethylenehtm

The Nature of Gibberellins (nd) Retrieved on 21st September 2011 from

httpwwwplant-hormonesinfogibberellinshtm

Pandey SD amp Sinha BK (2006) Plant Physiology (4th ed) Noida UP Vikas Publishing

House Pvt Ltd

Plant hormones (nd) Retrieved on 23rd September 2011 from

wwwbiog1105-1106orgdemos105unit5planthormonespdf

Plant hormones and growth regulators (nd) Retrieved on 24th September 2011 from

httpextensionoregonstateedumgbotanyhormoneshtml

Rastogi VB (2011) A COMPLETE COURSE IN ISC BIOLOGY-VOLII New Delhi Pitambar

Publishing Company Pvt Ltd