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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
http://www.psy.ritsumei.ac.jp/~akitaoka/sun.jpg
Red light(660 nm)
Pr
Pfr
• 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 RILunder 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
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)