Intrinsic factors part 1 Plant Growth Regulators

Prepared by,
Dr. Preeti D. Verma
Asst. Professor, Department of Pharmacognosy
L. M. College of Pharmacy, Ahmedabad.
INTRINSIC/ENDOGENOUS FACTORS
AFFECTING CULTIVATION OF
MEDICINALPLANTS - Part 1 (PGRs)
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1.
Plant Growth Regulators
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Prepared by Dr. Preeti D. Verma for
Academic Purpose Only

Definition
• PGRs are the organic compounds, other than nutrients,
which affect morphological structure and/or
physiological process of plant, in low concentration.
• Plant hormones are naturally occurring growth
regulators.
• It includes both Native (Endogenous) and Synthetic
(Exogenous) substances, which modify plant growth.
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Five Native PGRs: Auxin, Gibberellin, Cytokinin,
Abscisic acid and Ethylene.
Occurance
• They occur in different parts of plants and act at
different stages of growth and development.
• They can be found in many cells and tissues, although
plant hormones seem to be concentrated in meristems
and buds.
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General Mechanism of Action
• PGRs act on “Plant hormone receptors”.
• Control cell activities by sending chemical signals to cells to do
something or not to do something, including activating the genes
that code for specific enzymes.
• Plant hormones inhibit as well as promote cellular activities.
• They also work with environmental stimuli.
• Plant hormones often work in conjunction with each other, and
have overlapping effects.
• Most hormones have multiple effects in plants.
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Fig. Plant Growth Regulation involving Signal Pathways6

General Role : They play role in:
• Regulating cell enlargement
• Cell division
• Cell differentiation
• Organogenesis
• Senescence and
• Dormancy
Employed in seed treatment to achieve:
• Earlier growth and development
• Quality improvement like Protein level, Amino acid balance,
Production of secondary metabolites, etc.
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Since the external application of these plant
growth regulators have resulted in the
increased agricultural output of better
quality. Thus, they play an important role in
„Agricultural management of crops,
including medicinal plants‟.
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Classification of PGRs
Plant Growth Inhibitors
(PGI)
Plant Growth Stimulators
(PGS)
Plant Growth Regulators
(PGR)
1. Auxins
(A) Natural : E.g. IAA, IAN, PAA.
(B) Synthetic: E.g. IBA, NAA, NOA,
NAD, 2,4-D.
2. Gibberellins
3. Cytokinins
4. Brassinosteroids
1. Ethylene
2. Abscisic acid
(A) Natural : Abscisin-I,
Abscisin-II
(B) Synthetic: Maleic hydrazide
3. Jasmonic acid
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Plant Growth Stimulators
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[1] Auxins
• First phytohormone discovered.
• First isolated in 1926 from a plant : IAA i.e. Indole Acetic Acid.
• IAA is endogenously synthesized in plants (Principle Auxin).
• “Auxin” is general term used to indicate substances that promote
elongation of apical tissues.
Occurance:
• Present in larger concentration in shoot apical bud or meristems.
• Also Synthesized in: young leaves and seed embryo.
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Prepared by Dr. Preeti D. Verma for Academic Purpose Only

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Mechanism of Action:
a. IAA interacts with one or more components of
biochemical systems involved in synthesis of
proteins.
b. IAA alters the osmotically active contents of cell
vacuole during cell expansion or cell wall extension.

(A)Natural Auxins :
1) Indole acetic acid (IAA)
2) Indole-3-acetonitrile (IAN)
3) Phenylacetic acid (PAA)
4) 4-chloroindole-3- acetic acid.
Auxins
(B) Synthetic Auxins :
1) Indole-3-butyric acid (IBA)
2) α-napthyl acetic acid (NAA)
3) 2-napthyloxyacetic acid (NOA)
4) 1-napthylacetamide (NAD)
5) 2,4-dichlorophenoxy acetic acid
(2,4-D)
6) 5-carboxymethyl-N, N-dimethyl
dithiocarbamate.
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IAA

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Functions / Roles of Auxins in Plants:
Affects the root and shoot tips of the plant, as described below.
 Shoot Tip – No matter what the concentration, it promotes
growth in the shoot area of a plant (though higher concentrations
promote growth more).
Internode elongation by stimulating cell elongation (increase stem
length)
 Root Tip – High concentrations of auxin inhibit growth, while
small amounts are enough to promote growth in the root and cause
root initiation (adventitious roots in stem cuttings, etc.).

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Functions / Roles of Auxins in Plants:
Involved in different growth processes in plants, like
• Apical dominance (suppress growth of lateral buds)
• Cause tropisms (phototropism and gravitropism)
• Initiation/ Differentiaiton of vascular tissues (Xylem, Phloem)
• Promotes cambial activity (production of secondary growth)
• Delays leaf senescence (Loss of auxin initiates leaf abscission)
• Flower initiation
• Fruit setting (promote Parthenocarpy)
• Fruit growth and prevents its abscission

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Commercial uses of Auxins
1) IBA & NAA in combination: used in rooting of cuttings.
E.g.
Stem cuttings: Cinchona,Coffee, Pinus & Papaya.
Isolated leaves: Nicotiana & Datura spps.
2) NOA: used in Fruit-setting sprays.
3) 2,4-D: used both as PGR and in higher concentration as
selectiveweed killer. Remove dicot weeds, like Dandelion
from grass lawns.

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Effect of Auxins on Production of Secondary Metabolites OR
Application in Medicinal Plants:
1. On treatment with derivatives of NAA: Seedlings and young
plants of Mentha piperita, gave in the mature plants with an
increased yield (30-50%) of oil which itself contained 4.5-6.0%
more menthol.
2. Treatment with Auxins (IAA, NAA, 2,4-D): Increased alkaloid
production in submerged cultures of certain Ergot strains.
3. Treatment with 2,4-D: Increased Tropane alkaloids of Datura
spp., Morphological changes in the plants were observed (Increase
in trichome production).

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[2] Gibberellins
Discovered as metabolite of fungus
Gibberellafujikuroi, which caused
Bakane‟s disease in Rice plant.
Occurance:
Produced in roots, shoots and
younger leaves (buds), developing
fruits, seeds.
Highest concentration in
developing fruits & germinating
seeds. Prepared by Dr. Preeti D. Verma for Academic Purpose Only

21
Mechanism of Action of Gibberellins:
1. Promotes gluconeogenic enzymes during early stage of seed
germination:
Rapid conversion of lipid to sugar, which support growth and
development of the embryonic axis to root and shoot system.
2. Induce synthesis of α-amylase and other hydrolytic enzymes
during germination of monocot seeds.
3.They are also involved in mobilizing seed storage reserves
during germination and seedling emergence.

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Gibberellin A :
Isolated in 1938.
Mixture of 6 Gibberellins: GA1 , GA2 , GA3 , GA4 , GA7 ,
GA9.
GA3 : known as Gibberellic Acid.

Functions of Gibberellins in Plants
• Rapid elongation and division of stem tissue
(Reversal of genetic dwarfism)
• Breaking dormancy of seeds
• Flower initiation
• Fruit growth
• Induction of Parthenocarpy.
• Increase in size of leaves.
• Effect of Auxins & Gibberellins in cell growth is same i.e.
Increase in cell size (cell elongation).
Difference: Gibberellins : More effective in intact plants
Auxins : More effective on Excised organs. 23

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Effect of Gibberellins on Production of Secondary Metabolites :
1. Volatile oils:
(i) GA treatment of Chenopodium and Anethum spps : Increase volatile oil
content.
(ii) GA treatment on Mentha : Lowers the volatile oil content
(By reduction of the number of glandular hairs)
2. Alkaloids:
(i) Seeds of Atropa, Hyoscyamus & Datura: Exhibit protracted dormancy or
erratic germination. GA treatment of the seeds : Total and Uniform
germination.
(ii) GAtreatment of Catharanthus roseus & Rauwolfia serpentina : Lowers
alkaloidcontent. Prepared by Dr. Preeti D. Verma for

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3. Glycosides
(i) GA treatment of first year Digitalis purpurea plants :
Increase in cardiac glycosides
(ii) Application of GA to Cassiaangustifolia :
Reduce the sennosides content of the leaves,
But slightly increase the dry weight of the shoot.
4. Fixed oils:
GA treatment of Castor plants (Ricinus communis):
Increased height five times,
But no effect on quality & quantity of fixed oils.

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[3] Cytokinins
They are naturally occurring endogenous plant hormones or synthetic
substances, which induce cell division (growth and
differentiation).

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Occurance:
Actively dividing tissues of seed (embryo), seedlings, apical
meristems, fruits, root tips, leaves and wounded tissue sites.
Mechanism of Action:
• Regulation of Nucleic acid metabolism.
• Increase Protein synthesis.
• Transport of nutrients to cytokinin treated area: Prevents
Senescence.

(A) Natural Cytokinins :
1) Zeatin
2) N6-Dimethyl aminopurine
3) N6-Isopentenyl
aminopurine.
Cytokinins
(B) Synthetic Cytokinins :
1) Kinetin
2) Adenine
3) 6-Benzyl adenine benzimidazole
4) N,N’- Diphenyl urea.
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Functions of Cytokinins in Plants :
• Promote cytokinesis
• Retard leaf senescence
• Promote axillary bud growth
(by over-riding the apparent inhibiting effect of auxin)
• Induction of flowering

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Effect of Cytokinins on Productionof 2º Metabolites :
After kinetin treatment:
1. Duboisia hybrids : 18% increase in leaf yield and
16% increase in hyoscine content.
2. Leaves of the Coffee: Transient increase of up to 10% of caffeine
content.
3. Cassia angustifolia plants : Slight increase in sennosides
content and dry weight of shoots.
4. In Opium : Formation of elongated capsule, but reduced
alkaloid content.

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[4] Brassinosteroids:
Discovered in 1970s. (sixth class of phytohormone)
A Class of polyhydroxysteroids that promotes in stem
elongation and cell division
Brassinolide: The first isolated brassinosteroid, which
was discovered when the pollen
from rapeseed (Brassica napus) could promote stem
elongation and cell division
Occurance: In many plant parts: esp. Seeds, Stem,
Leaves, Pollens.

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Functions of Brassinosteroids :
1. Increase growth of young plant
tissues (cell expansion and cell
elongation)- works with auxins
2. Draught & Salinity resistance.
3. Tolerance to extreme temperature.
4. Resistance to pathogenic influence.
5. Self-healing towards herbicides.
Brassinolide

Plant Growth Inhibitors
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[1] Ethylene
• Natural plant growth inhibitor.
• Ethylene is the sole plant growth regulator known that is
present in the form of a Volatile Gas.
• Associated with Ripening, Flavour, Appearance &
Senescense of Fruits.

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Occurance:
• Ethylene is produced in many plant organs, esp. in
Ripening fruits, Fading flowers & Aging leaves prior
to Abscission.
• Present in very less quantity in plant, normally about
0.1 ppm.

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Functions of Ethylene :
1. Fruit ripening
2. Fruit Abscission
3. Leaf Abscission
4. Breaking Seed Dormancy (Germination of seeds)
5. Flower induction
6. Flower petal discolouration
7. Flower senescence
8. Inhibition of root and stem growth (length).

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Effect of Ethylene on Production of 2º Metabolites :
1. With low concentration of ethylene : Increase sennosides
concentration in Cassia angustifolia.
2. When applied to Tobacco leaves : Stimulate production of the
stress compounds Phytuberin and Phytuberol (these are
compounds produced in response to tobacco mosaic virus).
3. Ethephon (2-chloroethylphosphonic acid): Used for enhancing
the latex flow in rubber trees. When sprayed on scraped bark of
the rubber tree :
Increases latex yields more than 36%.Prepared by Dr. Preeti D. Verma for

38
[2] Abscisic Acid (ABA) :
Plant hormone which is responsible for Abscission of Leaves.
Occurance:
Ubiquitous in all higher plants.
Occur mainly in shedding leaves, fruits, flowers, stems.

(A) Natural ABA:
1) Abscisin I
2) Abscisin II
Abscisic Acid
(B) Synthetic ABA :
1) Maleic hydrazide
2) Daminozide
3) Glyphosine
4) Chlorophonium chloride
5) Piproctanyl bromide
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Mechanism of Action & Functions of ABA :
Released in Stress conditions, like mineral deficiency,
injury, drought, flooding : “Stress hormone”.
• Inhibits other plant growth substances.
• Inhibits GA-induced synthesis of α-amylase and other
hydrolytic enzymes in seeds (Cause Seed Dormancy).
• Promote Leaf Abscission.
• Promote Fruit Abscission.
• Anti-transpirant: Close the stomata when applied to
leaves. Prepared by Dr. Preeti D. Verma for

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Effect of ABA on Production of 2º Metabolites :
Spraying of ABA on plants of Datura stramonium &
Datura innoxia: Decreases height and Total alkaloid
content.

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[3] Jasmonic Acid :
• It is a cyclopentane acid.
• Isolated from a fungus in 1971.
Functions :
• Inhibits IAA-induced elongation of coleoptile tissues.
• Cause loss of Chlorophyll in leaves (leaves become
yellow coloured), followed by Senescence.

Intrinsic factors part 1 Plant Growth Regulators

Intrinsic factors part 1 Plant Growth Regulators

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Intrinsic factors part 1 Plant Growth Regulators