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Ch 39 Plant responses to internal and External Signals. Ch 38 (pgs 801-811) General plant information, read it. Signal Transduction pathways Receptor proteins Secondary messengers Protein kinases Calcium ion gated channels Transcription factors Phytochrome Hormones Analysis of
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Ch 39 Plant responses to internal and External Signals Ch 38 (pgs 801-811) General plant information, read it.
Signal Transduction pathways • Receptor proteins • Secondary messengers • Protein kinases • Calcium ion gated channels • Transcription factors • Phytochrome • Hormones • Analysis of • Research using Arabidosis (related mustard) (just like animals have used Drosophila) • Using mutant strands of plants (similar to Beadle and Tatum) • Molecular analysis
Phototropism (movement of growth towards light) • Research by Charles Darwin and son Francis • Remove tip and plant does not grow towards light • Place agar of chemicals in tip on plant and it grows straight • If placed on right side of plant, plant grows to left (increase length on dark side) • So chemical promotes growth, called it Auxin (cell growth hormone) • Differences between animal and plant hormones • Varying effects on varying plants • Varying quantities cause varying effects • Interact with each other to produce different effects
Types of Hormones • Auxin • Elongation of cells/stems* • Inhibits growth in the presence of Ethylene • Alters gene expression • Promotes fruit growth • Cytokinins • Controls cell division and differentiation in plants* • With Auxin might inhibit axillary growth of plant (still unclear though) • Slows apoptosis (cell death) • Gibberellins • Stem elongation and cell division • Fruit growth • Germination of seeds* • Promotes synthesis of amylase (breaks down starch in seeds)
Brassinosteriods • Similar to Auxin • When applied in dark, plants grow normal • Abscisis Acid • Promote seed dormancy* • Works antagonistically with gibberellins (ratio) • Drought signally (causing stomata to close) • Ethylene • Triple Response • Avoidance of obstacles (3 steps) • Senescene-programmed cell death • Loss of leaves • Fruit ripening* • Which triggers more ethylene • Important to understand pathway to prevent spoiling of fruit
Response to light • Blue light receptors • Phototropism • Opening of stomata • Inhibition of stem elongation • Phytochromes (red and far red light) • Red and far red are same peptide, but revert to different isomers • Seed germination • Phytochrome red (Pr)increases germination • Phytochrome far red(Pfr) decreases germination • Shade avoidance • P(fr) increases stem length • Due to blockage of red light by canopy • Helps keep track of circadian Rhythm • Circadian Rhythms-24 biological clock • Flowering
Photoperiodism • Short-day plants-flower when continuous night time hours are long • Long-day plants-flower when continuous night time hours are short • Day-neutral plants-are not affected by photoperiodism • Defense against Herivores • Physical defense (thorns, chemicals) • Mutual relationship with predatory insects (i.e. they lay eggs in flower) • Production of volatile substance that warns nearby plants of “attack” • Defense against pathogens • Gene-for-gene recognition • Pathogen derived molecules activate resistance genes in plants genome • Hypersensitive Response • Causes death in nearby plant tissue to stop spread • System Acquired Resistance • Plant-wide expression of defense genes. • Salicylic acid activates signal transduction pathways.
