Auxins and gibberellins would enhance stem elongation and fruit growth. - Auxins promote cell elongation and division, resulting in stem elongation. - Gibberellins also promote stem elongation by overcoming the inhibitory effect of other hormones. - Ethylene and cytokinins generally do not directly promote stem or fruit growth. Cytokinins promote cell division but not elongation. Ethylene inhibits stem elongation. - Abscisic acid and phytochrome are not directly involved in promoting stem or fruit growth. Abscisic acid inhibits growth and phytochrome regulates photoperiodism. Therefore, the correct answer is A - Auxins and gibberellins.

1. PLANT HORMONES
PROMOTE CELL DIVISION: CYTOKININS

2. WHERE IT PRODUCED ?
 Cytokinin are synthesized primarily in actively growing
tissues, particular in roots, embryos and fruits and
transported to other organs, although there are many
minor sites of production as well.
 Cytokinin produced in the root reach to their target
tissues by moving up the plant in the xylem sap.

3. HOW IT CONTROL CELL DIVISION
 Cytokinin will stimulate cell division and influenced the
pathway of differentiation when acting with auxin hormone.
 In some experiment, a piece of parenchyma tissue from
stem is cultured. This is some observation of the effect on
cytokinin in cell tissue
Abcent of cytokinin Added cytokinin & Added cytokinin only
auxin
The cell grow very The cell is grow and No effect
large but do not divide divided

4. HOW IT CONTROL CELL DIVISION
 The ratio of cytokinins to auxin controls the cell
differentiate.
 When the concentration of these 2 hormone are at certain
level, the mass of cell continues to grow, but remains
undifferentiated called a callus.
Cytokinin level increase Auxin level increase
Shoot buds develop from callus Root form

5. FUNCTION OF CYTOKININ
A list of some of the known physiological effects caused by
cytokinins are listed below
Stimulates Stimulates the
morphogenesis growth of lateral
Stimulates cell
(shoot initiation/bud buds-release of
division. formation) in tissue apical dominance.
culture.
Stimulates leaf
Cytokinins can slow
expansion resulting Slow deterioration
down the aging of
from cell of leaves on intact
some plant organs.
enlargement. plant.

7. STIMULATES ABSCISION & THE
REPENING OF FRUIT : ETHYLENE

8. WHERE IT PRODUCED?
Ethylene is the gaseous hormone that can be produced
by most all part of the plant.
It produced in high concentrations during senescence,
leaf abscission, and the ripening of some type of fruits.
This hormone synthesis is also stimulated by wounding
& stress (drought, flooding, mechanical pressure,
injury, & infection).

9. The triple response
to mechanical senescene
stress
Triple response is occur when Senescence is natural process aging
ethylene initiate a seedling to in plants
perform a growth maneuver
Ethylene play importance role e.g
In the triple response, stem shedding of a leaf in autumn,
elongation is slow, the stem withering of flower, & death of an
thicken & curvature causesthe annual after flowering
stem to start growing horizontally
Apoptosis = the onset of
programmed cell death,
It induced by mechanical stress
on the stem tip During apoptosis , newly formed
enzyme breakdown chemical
compound

10. Leaf Fruit
abscission ripening
The process of abscission
A burst of ethylene production in the
occurs in autumn when a
fruit help triggers the ripening process
leaf falls
A change in the ratio of A chain reaction occur during ripening
ethylene to auxin controls is
abscission. 1) ethylene trigger ripening.
2) ripening trigger more ethylene. E.g
positive feedback in physiologi
An aging leaf produces less
& less auxin and this make
the cell of the abscisssion Ethylene is gas , the signal to ripen to
layer more sensitive to ripen spread from fruit to fruit.for
ethylene example if you want to speed up fruit
ripening, storing it in paper bag.

11. Promotes bud & seed dormancy
abscisic

12. Where it produced?
 Almost plant has ability to synthesize
ABA.
 It presence has been detected in every
major organ & living tissue and may be
transported in the phloem/xylem

13. ABSCISIC ACID (ABA)
ABA is one of the hormone plant. Also called as
abscisic II & dormin
Function: inhibit growth, promote seed
dormancy & inhibit early germination, promote
stomatal closure during drought stress.
ABA also promotes abscission of leaves and
fruits
ABA inhibits stem elongation probably by its
inhibitory effect on gibberellic acid

14. EFFECT OF ABSCISIC ACID
SEED DORMANCY DROUGHT TOLERANCE
• One of major affect of ABA • ABA is the primary internal
is seed dormancy. Seed signal
dormancy has great survival - That enables plants to
value because it ensure that withstand drought
seed will germinate only - signaling turns on the
when there are optimal expression of genes
conditions of light, encoding proteins that
temperature, & moisture. protect cells — in seeds as
well as in vegetative tissues
• Many types of dormant seed
— from damage when they
germinate when ABA is
become dehydrated
remove or inactive.

15. a) ABA in roots that b) ABA in the stem that
elongate the root for allow the stem to elongate
water absorption to get sufficient light

16. Example of past year
question

17. 1) Name three (3) common types of plant
hormones and discuss the main functions of
each hormone (APR 2009)
A. Cytokinin
B. Ethylene
C. Abscisic

18. • stem apex, auxillary buds 
promotes cells division (release of
Cytokinins apical dominance)
• leaves  inhibits senescence
Abscisic • Guard cells  close stomata
• seed coat  inhibits seed
acid germination
•Stem  inhibits cell elongation
Ehtylene •fruits  promotes ripening

19. 2) Which plant hormones might be used to
enhance stem elongation and fruit growth?
(APR 2010)
A. Auxins and gibberellins
B. Ethylene and cytokinins
C. Abscisic acid and phytochrome
D. Phytochrome and flowering hormone