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Seeds – Part 3

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.

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Seeds – Part 3

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  1. 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 1) Morphological – embryo is not fully developed 2) Physiological – including: A) non-deep, intermediate, deep B) e.g., photodormancy, after-ripening, stratification

  2. Seeds – Part 3 Red light(660 nm) Pr Pfr Phy protein Phy action spectrum http://www.psy.ritsumei.ac.jp/~akitaoka/sun.jpg

  3. Seeds – Part 3 Red light(660 nm) Pr Pfr http://www.psy.ritsumei.ac.jp/~akitaoka/sun.jpg

  4. Role of light, ABA and GA in seed germination • 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)

  5. Germination is pretty complicated Photoreceptors and potential light-signalling intermediates

  6. Key points: • 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.

  7. Gibberelic acid (GA) synthesis pathway

  8. ABA synthesis pathway

  9. Pathway to germination involves many components

  10. Lab exercise: characterizing the germination response of the RILunder FR24-D light environment X Recombinant inbred line (RIL)‘Diplomat’ (Iceberg) X ‘Margarita’ (Butter) F1

  11. Recombinant Inbred Line (RIL) F2 ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. ….. F6 F5 F4 F3 F7 F1 Single seed descent F8 RIL population with 131 families (Dip x Mar)

  12. Germination in FR24-D environment is a complex (quantitative trait) Non-dormant Dormant Distribution of germination after exposure to FR-D among RIL (D X M)

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