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Biol 352 Lecture 5 Gibberellins: Regulators of Plant Height And Seed Germination January 22, 2007

Biol 352 Lecture 5 Gibberellins: Regulators of Plant Height And Seed Germination January 22, 2007. Review: Auxin Auxin was the 1 st plant hormone to be discovered Multiple pathways exist for auxin biosynthesis and metabolism

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Biol 352 Lecture 5 Gibberellins: Regulators of Plant Height And Seed Germination January 22, 2007

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  1. Biol 352 Lecture 5 Gibberellins: Regulators of Plant Height And Seed Germination January 22, 2007

  2. Review: Auxin • Auxin was the 1st plant hormone to be discovered • Multiple pathways exist for auxin biosynthesis and metabolism • Auxin is the only plant hormone known to be transported polarly; influx carrier, efflux carrier • Actions of auxin: cell elongation, phototropism, gravitropism • Developmental effects of auxin • Auxin signal transduction: auxin-induced genes, Aux/IAA. ARF, TIR1

  3. Lecture Outline: • GA structure and activity • GA biosynthesis • Experimental approaches: role of GA in stem elongation • Regulation of seed germination by GA • Summary

  4. Learning Objectives: • Define the key enzymes and key steps in GA biosynthesis pathways • Explain the experimental approaches used to demonstrate the role of GA in stem elongation • Explain the action of GA in seed germination • Compare IAA and GA signal transduction pathways • Reading: • 4th Ed, Plant Physiology, Taiz & Zeiger, Chapter 20: p461-491 • (3rd Ed, Plant Physiology, Taiz & Zeiger, Chapter 20 : p510-540)

  5. Discovery of Gibberellins • 1930s, Japan • Foolish rice • Gibberella fujikuroi

  6. GAx • x is a number, in the order of their discovery. • GAs are based on the ent-gibberellane skeleton. • Not all GAs are active. • GAs could be C-20 or C-19. • Oxidation state of C-2 and the number and position of hydroxyl groups are critical for the activity of GA.

  7. GA Biosynthesis • Major biosynthesis sites:immature seeds, developing fruits, young and actively growing buds, leaves, and upper internodes, roots. • Three stages • Three cellular compartments • Three key enzymes

  8. GA1 promoter:GUS GA biosynthesis occurs at multiple cellular sites

  9. Starts from Terpenoid • Stage 1: plastid; tetracyclic, ent-Kaurene • Stage 2: plastid envelop and ER; first GA (GA12)

  10. Stage 3: cytosol; C20-GAs, C19-GAs • Three key enzymes: GA20ox, GA3ox, GA2ox

  11. Developmental Effects of GA: • Stimulate stem elongation • Promote seed germination • Regulates the transition from juvenile to adult phases • Influence sex determination • Promote pollen development

  12. GA and stem elongation: • GA biosynthesis mutant (deficient and over-production mutant) • Correlation of stem elongation and endogenous GA level • Effect of exogenous GA • Overexpression of GA2ox

  13. 1. GA biosynthesis mutant—GA deficient mutants

  14. 2. Correlation of stem elongation and endogenous GA level

  15. 3. Effect of exogenous GA

  16. 4. Overexpression of GA2ox

  17. Relationship between auxin and GA

  18. GA signal transduction: • GA signal is perceived by receptor protein GID1. • GA induces gene expression. • Requires the degradation of transcriptional repressors.

  19. GA promotes seed germination

  20. Mode of action of GA in controlling -amylase gene expression

  21. Summary: • GA structure features • GA biosynthesis: 3 stages, 3 cellular compartments, 3 key enzymes • Experimental approaches: GA in stem elongation • GA signal transduction: seed germination

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