EXERCISE 17:
The Role of Light and Growth Regulators in Seed
Germination
GONZALES-MANOLONG-SOLIJON
INTRODUCTION
DORMANCY
• 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;
1. Must be viable2. Must be subjected to appropriate environmental conditions3. Any primary dormancy must be removed
• 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).
• 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
• 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)
OBJECTIVE
In this experiment the effect of light and certain growth regulators on seed germination will be investigated.
MATERIALS AND
METHODS
RESULTSAND
DISCUSSION
TREATMENTS REPLICATE 1 REPLICATE 2
Germinatedseeds
Percent germination
Germinatedseeds
Percent germination
1.Dark (Control) 5 10% 4 8%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 07. Green Light 0 0 0 08. Red Light 8 16% 6 12%9. Infrared 1 2% 0 0
Red light promotes germination
Phytochrome 660 Phytochrome 730(red absorbing) (far-red absorbing)
Far-red light inhibitsgermination
Figure 1. Effects of red and far-red light on the photochemically reactive pigment phytochrome and lettuce seed germinatio
• The membranes of the seed coats and/or the endosperm act as light sensors; once removed light control disappears.
4004104204304404504604704804905005105205305405505605705805906006106206306406506606706806907007107207307407500
10
20
30
40
50
60
Red Light
Wavelengths (nm)
Perc
ent t
rans
mitt
ance
(%)
Red Light
4004104204304404504604704804905005105205305405505605705805906006106206306406506606706806907007107207307407500
5
10
15
20
25
30
35
40
45
50
Blue Light
Wavelengths (nm)
Perc
ent T
rans
mitt
ance
(%)
4004104204304404504604704804905005105205305405505605705805906006106206306406506606706806907007107207307407500
10
20
30
40
50
60
Green Light
Wavelengths (nm)
Perc
ent T
rans
mitt
ance
(%)
4004104204304404504604704804905005105205305405505605705805906006106206306406506606706806907007107207307407500
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Far-red Light
Wavelength (nm)
Perc
ent T
rans
mitt
ance
(%)