Plant growth is regulated by phytohormones such as auxins, gibberellins, cytokinins, ethylene, and abscisic acid. Auxins promote cell elongation and differentiation, apical dominance, phototropism, and root initiation. Gibberellins promote seed germination, stem elongation, and flowering. Cytokinins promote cell division, chloroplast development, and counteract apical dominance. The document discusses the biosynthesis, physiological effects, and bioassays of these major plant hormones.

1. Growth
Hormones

2. Most of the physiological activities and
growth in plants are regulated by the action
and interaction of some chemical substances
in them called as phytohormones.
Plant hormone is defined as “organic
substance produced naturally in the higher
plants, controlling growth or other
physiological functions at a site remote from
its place of production and active in minute
amounts.”

4. * The rate of growth of a plant or plant part
is not always the same during its life.
Sometimes it is slow and at other times
rapid. If we plot the increase in cell number
(growth rate) against time, a typical S-
shaped curve is obtained. This is called
growth curve or sigmoid growth curve.
plant growth is: a permanent and
irreversible increase in size and form
attended by an increase in weight.

5. This curve has three phases of growth.
(i) Lag Phase – This is the initial phase of growth
when the rate of growth is very slow.
(ii) Log Phase – It shows rapid growth and is
maximum during the entire life span.
(iii) Stationary Phase – Here the rate of growth
starts decreasing and finally it stops

9. Monocot leaf area= length x width x 0.75
Dicot leaf area= (area of square x weight of
leaf)/weight of square

10. There are 5 mail classes of plant
growth hormones :

12. AUXIN

13. Biosynthesis of Auxin (IAA) in
plants

14. Physiological effects of Auxins:
1-Cell Elongation
2- Apical Dominance
3- Tropism
4- Root Initiation
5- Prevention of Abscission
6- Parthenocarpy
7-Vascular Differentiation

15. Bioassay of auxin
A (Avena coleoptile):
1) Sterilized seeds of hordium are allowed to
germinate on moist filter paper for 4 days
until appearance and slight elongation of
coleoptile.
2) After removing coleoptile apex, cut
sections about 1cm in length.
3)Prepare different concentrations of auxin
(0, 0.001, 0.01, 0.1, 1 and 10 ppm)
3)For each conc. Prepare 3 replicates
petridishes each containing 5 hordium
sections and 10ml of the solution
4)Incubate in dark for 24hrs

16. B) Cress root inhibition test :
1) Sterilized seeds of Cress are allowed
to germinate on moist filter paper for 24
hrs.
2) Prepare different concentrations of
auxin (0, 0.001, 0.01, 0.1, 1 and 10 ppm)
3)For each conc. Prepare 3 replicates
petridishes each containing 5 seeds and
10ml of the solution
4)Incubate in dark for 48hrs
5) Measure the length of the roots
then calculate % of increase in length
and plot graphically.

19. Aim: Role of auxin in
apical dominance

22. Aim: Role of auxin in
phototropism

23. Aim: Role of auxin in
geotropism

24. 1- Cut 3 potato cubes of
approximately equal initial
weight
2-
Aim: Role of auxin in
active wateruptake

25. 3-Rewight the 3 cubes each 10
minutes for 1 hr
4- Calculate %of change in
weight=
((final wt – initial wt)/initial wt
)*100
5- Draw your curve and
comment on your results
reffering to the role of auxin
in active water uptake

26. Gibberellin

27. Biosynthesis of gibberellins in
plants

28. Physiological effects of
gibberellin:
1- Seed germination
2- Overcome dwarfism
3- Dormancy of Buds
4- Elongation of the
Internodes
5- Bolting and Flowering

29. Bioassay of gibberellin
1) Sterilized seeds of lettuce are allowed
to germinate on moist filter paper for 2
days until appearance of radicle.
2)Prepare different concentrations of
gibberellin (0, 0.001, 0.01, 0.1, 1 and 10
ppm)
3)For each conc. prepare 3 replicates
petridishes each containing 5 seeds
sections and 10ml of the solution
4)Incubate in dark for 48hrs
5)Lengths of the hypocotyl are measured
then % of increase in length was
calculated and plotted graphically.

30. 5)Lengths of the hypocotyl are
measured then % of increase in
length was calculated and
plotted graphically.
% increase in length= (final
length /final control length)*100

31. Role of gibberellin in
hydrolytic enzymes
production during seed
germination
1) Cut barley grains in to 2 pieces
horizontally (embryo +
embryoless parts
2) Prepare solid agar and starch
media,then after cooling prepare

33. 3)Incubate f0r 48 hrs in dark,
then test with iodine and
comment on your result

35. Effect of gibberellin on
plant dwarfism

36. Cytokinin

37. Physiological effects of
cytokinin:
1- Cell division and
enlargement
2- Counteraction of apical
dominance
3-Promotion of chloroplast
development
4-Promotion of hydrolytic

38. Biosynthesis of cytokinins in
plants

39. Bioassay of cytokinin (effect
of cytokinin on cell (division
and enlargement) and
chlorophyll content in
cotyledon leaf ).
1) Sterilized cucumber or
sunflower seeds are allowed to
germinate on moist filter paper for
4 days until appearance and
swelling of the cotyledonary
leaves .
2) Cut sections of (1cmx1cm)

40. 3)Prepare different concentrations
of cytokinin (0, 0.001, 0.01, 0.1, 1
and 10 ppm)
4)For each conc. prepare 3
replicates petridishes each
containing 5 sections and 10ml of
the solution
4)Incubate in dark for 48hrs
5)Lengths and width of the

41. Effect of cytokinin on
chlorophyll content

42. 1- The treated cotyledon
segments treated by cytokinin
were weighted for each
concentration and ground in
dark
by 15 ml acetone85%

43. 3- The supernatent was
measured at 452, 645 and
664nm
4- Chlorophyll content was
calculated as following :