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Plant Development and Signals Plants use development to solve ecological problems

Plant Development and Signals Plants use development to solve ecological problems Repair, maintain, flourish Resist competitors, herbivores, pathogens, abiotic factors Seek out resources Plants respond to environmental and endogenous signals

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Plant Development and Signals Plants use development to solve ecological problems

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  1. Plant Development and Signals Plants use development to solve ecological problems • Repair, maintain, flourish • Resist competitors, herbivores, pathogens, abiotic factors • Seek out resources Plants respond to environmental and endogenous signals Signals alter gene reading programs and influence: • Cell division, expansion and differentiation at meristems • Tissue, organ and whole plant modification • Fitness

  2. Gene reading programsand flow of information DNA gene promoter m RNA transcript + - + - + - Protein synthesis Signal(s) + - protein enzymes cytoskeletal + - regulatory transporter structural

  3. Classes of signals Internal (endogenous); generally chemical • Hormone • Non-hormone • Electrical gradients (but much less so than animals) External, generally non-chemical • Electrical, light, gravity, temperature, mechanical forces • Some chemical cues (e.g. MeJ)

  4. Internal chemical signals Hormones (a definition from animal biologists) • Naturally occurring organic molecules that act in small concentrations • Sole function is to serve as a developmental signal • Signal is context dependent • Typically move from source to target Plant biologist- naturally occurring organic molecule whose sole function is to serve as a development signal • 5 classes of plant hormones

  5. Auxin • Indoleacetic acid (IAA), IBA • Activity determined by charge separation • Many synthetics • Roles: + 0.55 nm -

  6. Gibberellins (GA) • Large family of compounds • Numbered according to discovery • Three linked rings with side groups • Roles:

  7. Cytokinins (CK) • Derivative of adenine • Different functional (R) groups attached • Roles: R group

  8. Ethylene (C2H4) • Gas at room temperature • Roles: H H C C H H

  9. Abscisic acid (ABA) • Named b/c it was discovered in abscised lvs • Not the direct cause of leaf loss though • Roles:

  10. Internal non-hormone chemical signals Phenolics (Phe) • Coumarin • Anthocyanin • Salicylic acid • Ferulic acid R O

  11. Methyl jasmonate (MeJ) • Related to stress response(s) • Root initiation, tendril coiling, pollen germination • Volatile interspecies ‘messages’

  12. Oligosaccarides (Oligos) • Polymers of carbohydrates • Related to defense response • Phytoalexins, chitinase, and protease inhibitors

  13. External chemical signals • Nitrate (NO3-) • Controls nitrogen assimilation • Hydroquinones • Can signal parasitic plants to start ‘parasite gene reading program’

  14. Principles of plant hormone action • Each hormone causes many responses IAA - Abscission + Root initiation + Stem elongation - + Bud expansion Vascular repair

  15. Principles of plant hormone action • A hormone’s effect can differ between organs and species, and with age. Wheat seedling elongation Stem elongation + 10-6 IAA - Root elongation

  16. Principles of plant hormone action 3. Many hormones can affect the same response CK IAA GA + + + Cell division

  17. Hormone sensors Since signals vary, the meaning of a signal depends on receptors and sensitivity (kinds of sensors a cell contains) Cells must have sensors/receptors; when hormone binds w/ following (blue) molecules response set off • Membrane channels or carriers receive and transport signal (A) • Signal activates enzyme (CD) • Receptor is regulatory protein (B) A + - A Gene reading + - + + - C D B

  18. Setting off a response Responses may occur when the cell has a threshold number of receptors bound to hormones Equilibrium conditions predicts that response can occur when: • Hormone concentration increased • Receptor concentration increased (= sensitivity) Hormone Receptor Response + HR

  19. Response depends on concentration • Induction – on/off response once threshold hormone level is exceeded • Modulation – on-going log linear dose response 100% Response 0% [Hormone] Physiologic range Response 10-8 10-6 [Hormone]

  20. Hormone concentration control • Synthesis • Transport • Destruction • Sequestration • Conjugation • Example - IAA

  21. Concentration control • Self-inhibition • Interactions between IAA and C2H4 • Interactions between CK and GA • De-stabilizing concentrations

  22. Measuring hormone concentrations • Bioassays • Grow specimens in a range of known concentrations • Generate dose response curve • Find value for unknown • Chromatography • Mass spectrometry • Antibody

  23. Phenylalanine + gene PAL + Cinnamic acid aa Cinnamyl CoA Lignin + + gene Chalcone synthase Chalcone Phenolics and flavonoids, including some phytoalexins Control of phenolic synthesis Phenolics may act as 2o messengers + Ferulic acid Injury Pathogens +

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