ECONOMY AND TYPES PPT

1. Plant hormones

2. Plant hormones
Plant hormones or phytohormones are the
physiological intercellular representatives that are
needed to control the complete lifecycle of a plant.
It includes germination, rooting, growth, flowering,
fruiting and death of the plant. Plant growth
regulators often termed as plant growth factors are
usually employed for plant hormones or substances
of similar effect that are administered to plants. The
application of growth regulators allows
synchronization of plant development to occur.

3. Difference between plant growth hormone and plant growth retardant
Plant hormone Plant regulator
Plant hormones are natural Plant growth regulators are mainly synthetic
Plant hormones are synthesized by the plants
themselves and are effective at low
concentrations which on high concentration
can be dangerous.
Plant growth regulators are characterized by their
low rates of application; high application rates of the
same compounds often are considered herbicidal
Plant growth hormones are chemical
substances other than nutrients produced by
plants in small quantities at one place and
transported to the place of action.
Plant growth regulators are any substance or
mixture of substances intended, through
physiological action, to accelerate or retard the rate
of growth or maturation, or otherwise alters the
behavior of plants or their produce.
These growth hormones may promote or
inhibit or otherwise modify growth and
development.
Plant growth regulators are chemical substances
applied exogenously to promote or inhibit or
otherwise modify growth and development.

4. Growth Promoters
(i) Auxins: Auxins in plants mainly control the growth of the plants by
cell enlargement. These may function as a stimulator as well as an
inhibitor for plants. Growth in varied plant parts act differentially to
these compounds for instance at very low concentrations, 2,4-D
stimulates cell elongation in plants whereas, at high concentrations it
inhibits enlargement and even turns out to be toxic to plants. The auxin
like substances are produced in buds, tips of stem, roots etc. Auxins also
stimulate differentiation of cells, formation of roots in plant cuttings and
formation of xylem and phloem tissues in the plants. Some of the
synthetic substances having auxin activity are IAA, IBA, NAA etc.

5. Functions of Auxin
1. Stimulates cell elongation
2. Stimulates cell division in the cambium and, in
combination with cytokinins in tissue culture
3. Stimulates differentiation of phloem and xylem
4. Stimulates root initiation on stem cuttings and lateral
root development in tissue culture
5. Mediates the tropistic response of bending in response
to gravity and light
6. The auxin supply from the apical bud suppresses
growth of lateral buds

6. (ii) Gibberellins: Gibberellins are plant regulators which
controls cell division and cell elongation in plant shoots. This
kind of substances stimulate growth in tissues of young
internodes e.g. GA3. It acts by:
a. Modifying RNA produced in nuclei i.e. it has control over cell
elongation.
b. Cell elongation by hydrolysis of starch leads to increased
concentration of sugar in cell sap, inturn it makes entry of water
and finally stretches the cell size.

7. Functions of Gibberellins
1. Stimulate stem elongation by stimulating cell division and elongation.
2. Stimulates bolting/flowering in response to long days.
3. Breaks seed dormancy in some plants which require stratification or
light to induce germination.
4. Stimulates enzyme production (a-amylase) in germinating cereal
grains for mobilization of seed reserves.
5. Induces maleness in dioecious flowers (sex expression).
6. Can cause parthenocarpic (seedless) fruit development.
7. Can delay senescence in leaves and citrus fruits.

8. (iii) Cytokinin: Cytokinins interacts with auxins. These are
substances composed of hydrophilic group of higher specificity (adenine)
and one lipophilic group without specificity. The cytokinins form a group
of plant hormones having similar effects as those of gibberellins in
breaking the dormancy of a wide range of seeds and in increased fruit
set. These hormones mainly stimulate cell divisions and prevent
chlorophyll degradation. It acts on cell initiation/cell division. When
Cytokinin: Auxin ratio is more, shoot development will be more. The
prevalence of equal ratio leads to undifferentiated callus production.

9. Functions of Cytokinin
1. Stimulates cell division.
2. Stimulates morphogenesis (shoot initiation/bud formation) in
tissue culture.
3. Stimulates the growth of lateral buds-release of apical
dominance.
4. Stimulates leaf expansion resulting from cell
enlargement.
5. May enhance stomatal opening in some species.
6. Promotes the conversion of etioplasts into chloroplasts via
stimulation of chlorophyll synthesis.

10. Plant Inhibitors:
(i) Abscisic acid (ABA): It is a naturally occurring
sesquiterpene which regulate plant growth and metabolism in
various ways and have been detected in nearly all plants. It is
involved in the abscission of plant organs, induction and
vegetative buds, in regulation of fruits repining and generally in
reduction of growth. These are basically the plant regulators
which inhibit the catalytic action of specific enzymes.

11. Functions of Abscisic acid
1. Stimulates the closure of stomata (water stress brings about
an increase in ABA synthesis).
2. Inhibits shoot growth but will not have as much affect on
roots or may even promote growth of roots.
3. Induces seeds to synthesize storage proteins.
4. Inhibits the affect of gibberellins on stimulating de novo
synthesis of ǯ-amylase.
5. Has some effect on induction and maintenance of
dormancy.
6. Induces gene transcription especially for proteinase
inhibitors in response to wounding which may explain an
apparent role in pathogen defense.

12. (ii) Ethylene: it is the only gaseous hydrocarbon hormones which plays an
important role in the ripening of fruits, inhibition of root growth, abscission and
other growth processes. Unlike the other hormones, ABA and Ethylene are not
discovered through any interaction with fungi.
Functions of Ethylene
1. Stimulates the release of dormancy.
2. Stimulates shoot and root growth and differentiation (triple response)
3. May have a role in adventitious root formation.
4. Stimulates leaf and fruit abscission.
5. Stimulates Bromiliad flower induction.
6. Induction of femaleness in dioecious flowers.
7. Stimulates flower opening.
8. Stimulates flower and leaf senescence.

13. Plant growth retardants:
Main action of these chemicals is retardation of stem elongation by
preventing cell division in subapical meristem. For e.g. SADH, phosphon-D,
CCC etc.
Some of the growth regulators widely used in horticultural crops are:
 NAA (Naphthalene acetic acid)
 GA (Gibberellic acid)
 Ethrel
 CCC (Cycocel)
 MH (Maleic hydrazide)
 2,4-D
 Triacontanol
 2, 4, 5-T