This is about the role of phytohormones and light in the germination of seeds.

1. GONZALES-MANOLONG-SOLIJON

3. • A temporary suspension of visible growth of
any plant structure containing a meristem
(Lang 1987).
• After embryo and endosperm development
• To initiate germination, three conditions must
be met;

4. 1. Must be viable
2. Must be subjected to appropriate
environmental conditions
3. Any primary dormancy must be removed

5. • Light has been recognized around the mid-
nineteenth century as a critical factor
controlling germination (Crocker, 1930).
• The photochemically reactive pigment
Phytochrome has been shown to be involved
in the mechanism of light sensitivity in seeds
(Bewley and Black, 1985).

6. • When an imbibed seed is exposed to red light
(600-760 nm) phytochrome (P) changes to Pfr
which promotes germination.
• When exposed to far-red light (760-800 nm),
inhibits germination

7. • Specific endogenous plant growth substances
have important roles in the control of
dormancy.
• Most of these are;
– Abscisic Acid (ABA)
– Gibberellinc Acid (GA)
– Cytokinins
– Others (Indoleacetic Acid, Kinetin, Auxin)

8. In this experiment the effect of light and certain
growth regulators on seed germination will be
investigated.

12. TREATMENTS REPLICATE 1 REPLICATE 2
Germinated Percent Germinated Percent
seeds germination seeds germination
1.Dark (Control) 10% 4 8%
5
2. White Light 4 8% 4 8%
3. W/ GA3 + Dark 10 20% 10 20%
4. w/ IAA + Dark 4 8% 1 2%
5. w/ ABA + White 4 8% 1 2%
6. Blue Light 0 0 0 0
7. Green Light 0 0 0 0
8. Red Light 8 16% 6 12%
9. Infrared 1 2% 0 0

13. Red light promotes germination
Phytochrome 660 Phytochrome 730
(red absorbing) (far-red absorbing)
Far-red light inhibits
germination
Figure 1. Effects of red and far-red light on the photochemically reactive
pigment phytochrome and lettuce seed germinatio

14. • The membranes of the seed coats and/or the
endosperm act as light sensors; once removed
light control disappears.

15. Red Light
60
50
40
Percent transmittance (%)
30
20
10
0
400 500 600 700
Wavelengths (nm)

16. Blue Light
50
45
40
35
Percent Transmittance (%)
30
25
20
15
10
5
0
400 500 600 700
Wavelengths (nm)

17. Green Light
60
50
40
Percent Transmittance (%)
30
20
10
0
400 500 600 700
Wavelengths (nm)

18. Far-red Light
4.5
4
3.5
3
Percent Transmittance (%)
2.5
2
1.5
1
0.5
0
400 500 600 700
Wavelength (nm)