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

(%)