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etiolation
morphological adaptations for growing in darkness
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De-etiolation
after exposure to light, when shoots and roots grow normally
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Reception
internal and external signals are detected by receptors, proteins that change in response to specific stimuli
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Transduction
second messengers transfer and amplify signals from receptors to proteins that cause responses
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Response
- -a signal transduction pathway leads to regulation of one or more cellular activities
- -these responses to stimulation involve increased activity of enzymes
- -this can occur by transcriptional regulation or post transductional modification
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Transcriptional regulation
specific transcription factors bind directly to specific regions of DNA and control transcription of genes
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Positive transcription factors
proteins that increase the transcription of specific genes
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negative transcription factors
proteins that decrease the transcription of specific genes
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Post-translational modification
- involves modification of existing proteins in the signal response
- -often involves the phosphorylation of specific amino acids
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Hormones
chemical signals that coordinate different parts of an organism
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Charles Darwin and his son Francis conducted experiments on phototropism, what did they find?
that grass seedling could bend toward light only if the tip of the coleoptile was present
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phototropism
a plant's response to light
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Boysen- Jensen continued the phototropism experiment how?
tip is separated by a gelatin permeable barrier or an impermeable one
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Auxin
- refers to any chemical that promotes elongation of coleoptiles
- -IAA is one common in plants
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Auxin transporter proteins
move the hormone from the basal end of one cell into the apical end of the neighboring cell
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Role of auxin in cell elongation
- stimulates the proton pumps in the plasma membrane
- -proton pumps lower the pH in the cell wall
- -expansins loosen cellulose and the cell can elongate
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expansins
enzymes that loosen the cell wall's fabric
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auxins are used as what for lawns?
herbicides
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auxin affects what by inducing cell division in the vascular cambium and influencing differentiation of secondary xylem
secondary growth
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cytokinins
- stimulate cytokinesis (cell division)
- produced in actively growing tissues (roots, embryos, and fruits)
- work with auxin to control cell division and differentiation
- inhibit protein breakdown
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Gibberellins
stimulate growth of leaves and stems
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Fruit growth
both auxin and gibberellins must be present for fruit to set
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Germination
after water is imbibed, release of gibberellins from the embryo signals seeds to germinate
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brassinoidsteriods
- -chemically similar to the sex hormones of animals
- - induce cell elongation and division in stem segments
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Acid ABA
- -slows growth
- seed dormancy -ensures that seed will germinate only in optimal conditions
- -primary internal signal that enables plants to withstand drought
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ethylene
- produced in response to stresses such as drought, flooding, mechanical pressure, injury, and infection
- -effects response to mechanical stress
- senescence
- leaf abscission
- fruit ripening
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ethylene induces the triple response which allows a growing shoot to avoid obstacles, what are the three responses
- -slowing of stem elongation
- -thickening of the stem
- -horizontal growth
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senescence
- programmed death of plant cells or organs
- -a burst of ethylene is associated with apoptosis
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apoptosis
the programmed destruction of cells, organs, or whole plants
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leaf abscission
- a change in the balance of auxin and ethylene controls leaf abscission
- -triggered by a burst of ethylene production (one bad apple spoils the bunch)
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