Transcript Control Systems in Plants
Control Systems in Plants
Etioloation and De etiolation
Plant Hormones
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What is a Plant hormone?
• Compound produced by one part of an organism that is translocated to other parts where it triggers a response in target cells and tissues.
Experiments on Phototropism Discovery of Hormones
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Went – – Modified Boysen-Jensen experiments Extracted the chemical messenger responsible
Functions of Plant Hormones
• Control plant growth and development by affecting division, elongation, and cell differentiation • Effect depends on size of action, stage of plant growth and hormone concentration • Hormonal signal is amplified by gene expression, enzyme activity, or membrane properties
Five Classes of Plant Hormones
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Which hormones cause the following….
• Apical dominance from apical bud • Abscission • Stimulates growth of axillary buds • Root growth • Stimulates closing of stomata • Causes fruit ripening • Stimulates seeds to break dormancy and germinate • Growth inhibitor • Cell division and differentiation • Cell elongation • Seedless fruit
Which hormone is made at each location?
• Made in roots and transported upwards • Found in meristems of apical buds and seed embryos • Found in tissues of ripening fruit • Leaves stems, roots and green fruit
Which hormone caused the following?
Opposing hormones
• Which two hormones act in opposition to one another regarding apical dominance, cell division and differentiation?
• Which two hormones work in opposition regarding seed dormancy?
Phototropism
Acid Growth Hypothesis
Plant Movement
• A. Tropisms: – growth response toward or away from stimuli • 1.
– cells on darker side of shoot elongate faster than cells on bright side due to auxin distribution – auxin move laterally across the tip from the bright to dark side by an unknown mechanism.
– Cells on the dark side grow
• 2. Gravitropism (geotropism) – gravity – roots --> positive geotropism – stems---> negative geotropism
– starch grains in root cap cells, they trigger calcium redistribution which results in auxin movement in root – auxin inhibits cell elongation – upperside of root elongates faster than bottom
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• growth in response to touch • tendrils contacts solid and coils • increased production of ethylene • 4. Hydrotropism • growth toward water • willow tree
Circadian Rhythms and the Biological Clock
• Photoperiodism – a physiological response to DAY length – seasonal events
• Photoperiods Control of Flowering – the amount of night length controls flowering • 1.
– late summer, fall and winter • 2.
– late spring and summer • 3. Day- Neutral plants – unaffected by photoperiods
Critical Night Length
• Night (dark) actually causes flowering not light – Leaves detect the photoperiod while buds produce flowers • Florigen – scientists believe this unidentified hormone is produced in the leaves and moves to buds.
Phytochrome
• Protein containing chromophore (light absorbing component) responsible for a plant’s response to photoperiod – P r - red absorbing – P fr - Far red absorbing • Plants synthesize Pr in dark – if phytochrome illuminated then Pr Pfr since both types of light are seen • P fr triggers many plant responses to light • In darkness P fr goes back to P r
Response to Stress
• Water deficit
• Salt Stress • Heat Stress • Cold Stress • Herbivores…
Defense Against Pathogens
• Gene for Gene relation between plant and pathogen • Coevolution between plant and pathogen
Short Day Plant
Short Day Plant
• Spinach Long Day Plant Spinach Long Day Plant
Which wave length of light causes photo tropism?
Auxins IAA indoleactetic acid: natural auxin
• Promotes elongation & secondary growth • Apical meristem is the major site of auxin production • Inhibits lateral growth • Induces female floral parts & fruit
Cytokinins
• Move from the roots to tissues by moving up xylem • Works with auxin to promote differentiation • Stimulates protein synthesis • Made in roots • Function: – 1. Cell division and differentiation – 2. Apical dominance – 3. Anti-aging hormones • slow protein deterioration
Observe Apical Dominance
Gibberellins
• Stimulate elongation of cells • Inhibits root growth • Stimulate flower part development bolting(large internode) • Works with auxin for fruit development • Signals seeds to break dormancy and germinate
Abscisic Acid (ABA)
• Growth inhibitor • returns seeds to dormancy • inhibits cell division in vascular cambium • causes rapid closing of stoma during dry periods • promotes positive geotropism
Ethylene
• Gaseous hormone • high [auxin] induce release of ethylene • fruit ripening (positive feedback) • Apoptosis: – Senescence (aging) – Abscission – leaves falling