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 Red light (660 nm) PrPr P fr Phy protein Phy action spectrum

Seeds – Part 3 Red light (660 nm) PrPr P fr

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 F1F1 Recombinant inbred line (RIL) ‘Diplomat’ (Iceberg) X ‘Margarita’ (Butter) Lab exercise: characterizing the germination response of the RIL under FR 24 -D light environment

11 Recombinant Inbred Line (RIL) F1F1 F3F3 ….. F4F4 F5F5 F6F6 F7F7 Single seed descent RIL population with 131 families (Dip x Mar) F2F2 ….. F8F8

Distribution of germination after exposure to FR-D among RIL (D X M) Dormant Non-dormant Germination in FR 24 -D environment is a complex (quantitative trait)