Seeds – Part 3

1. Dormancy

b.) Primary: dormancy that is initiated during seed development

i. Exogenous 1) Physical – e.g., seed coat, fruit parts Scarification may be needed

2) Chemical – chemicals produced by seed or fruit Leaching may be needed

ii. Endogenous

A) non-deep, intermediate, deep

2) Physiological – including:

1) Morphological – embryo is not fully developed

B) e.g., photodormancy, after-ripening, stratification

Seeds – Part 3

http://www.psy.ritsumei.ac.jp/~akitaoka/sun.jpg

Red light (660 nm)

Pr

Pfr

Phy protein

Phy action spectrum

Seeds – Part 3

Filtered light (far-red) 730 nm

Pfr

Pr

• Seed germination in most angiosperms is under the regulation of multiple hormonal pathways and other signaling molecules.

• The gibberellin-abscisic acid (GA-ABA) balance is pivotal in controlling germination, with GA promoting and ABA inhibiting germination

• Light also controls endogenous GA and ABA levels during seed germination

• GA appears to regulate ABA catabolism during high temperature imbibition in lettuce

• Red and far-red light are sensed by five different phytochromes in Arabidopsis (PHYA to PHYE)

Role of light, ABA and GA in seed germination

Germination is pretty complicated

Photoreceptors and potential light-signalling intermediates

• Germination of lettuce (Lactuca sativa L.) and other light-sensitive seeds are regulated by phytochrome.

• The requirement for red light is circumvented by the application of gibberellin (GA).

• The endogenous content of GA1, the main bioactive GA in lettuce seeds, increases after red-light treatment.

Key points:

Gibberelic acid (GA) synthesis pathway

ABA synthesis pathway

Pathway to germination involves many components

10

X

F1

Recombinant inbred line (RIL) ‘Diplomat’ (Iceberg) X ‘Margarita’ (Butter)

Lab exercise: characterizing the germination response of the RIL under FR24-D light environment

11

Recombinant Inbred Line (RIL)

F1

F3

….. ….. ….. …..

F4

….. ….. ….. …..

F5

….. ….. ….. …..

F6

….. ….. ….. …..

F7

….. ….. ….. …..

Single seed descent

RIL population with 131 families (Dip x Mar)

F2 ….. ….. ….. …..

F8

0

10

20

30

40

50

60

70

80

90

100

178.2

243

116.2

139

218

177 88 10

118

9 83 173

124 92 16

324

022

1 410

.3 55 81 244 65 18

822

220

2 41 43 3D 89 130

138

217.2

111

194 28 93 12 19

3 3L 233

14.1 54

Family Number

Fin

al g

erm

ina

tio

n (

%)

Distribution of germination after exposure to FR-D among RIL (D X M)

Dormant

Non-dormant

Germination in FR24-D environment is a complex (quantitative trait)