Plant Responses to Stimuli Flashcards
What are the mechanisms of signaling
Reception, Transduction, Response
Reception
Internal and external signals are detected by receptors, proteins that change in response to specific stimuli
Transduction
Second messengers transfer and amplify signals from receptors to proteins that cause responses
Response
A signal transduction pathway leads to regulation of one or more cellular activities
In most cases, these responses to stimulation involve increased activity of enzymes
This can occur by transcriptional regulation or post translational modification
Specific transcription factors
bind directly to specific regions of DNA and control transcription of genes
Positive transcription factors
proteins that increase the transcription of specific genes, while negative transcription factors are proteins that decrease the transcription of specific genes
Post-translational modification
modification of existing proteins in the signal response
What does modification often involve
the phosphorylation of specific amino acids
Phototropism
a plant’s response to light
Auxin
any chemical that promotes elongation of coleoptiles
Indoleacetic acid (IAA)
a common auxin in plants
Role of auxin transporter proteins
move the hormone from the basal end of one cell into the apical end of the neighboring cell
What is the role of auxin in cell elongation
auxin stimulates proton pumps in the plasma membrane
Proton pumps lower the pH in the cell wall, activating expansions, enzymes that loosen the wall’s fabric
With the cellulose loosened, the cell can elongate
How does auxin affect secondary growth
by inducing cell division in the vascular cambium and influencing differentiation of secondary xylem
What are two kinds of synthetic auxins
Naphthalene acetic acid (NAA) and indolebutyric acid (IBA)
What do synthetic auxins do
prevent abscission in apples and berries
Promote flowering and fruiting in pineapples
2,4-dichlorophenoxyacetic acid (2,4-D)
a herbicide commonly used to kill weeds
What do cytokinins do
stimulate cytokinesis
Where are cytokinins produced
in actively growing tissues such as roots, embryos , and fruits
what is the role of cytokinins
work together with auxin to control cell division and differentiation
Retard the aging of some plant organs by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues
Control of Apical Dominance
Cytokinins, auxin, and other factors interact in the control of apical dominance, a terminal bud’s ability to suppress development of axillary buds
What happens if the terminal bud is removed
the plants become bushier
Strigolactones
Inhibit axillary bud growth
Affect extent of branching
Derived from caretonoid
Role of Gibberellins
Stem Elongation, Fruit growth, Germination
Stem Elongation
Gibberellins stimulate growth of leaves and stems
In stems, they stimulate cell elongation and cell division
Fruit growth
In many plants, both auxin and gibberellins must be present for fruit to set
Gibberellins are used in spraying of Thompson seedless grapes
Germination
After water is imbibed, release of gibberellins from the embryo signals seeds to germinate
Brassinosteroids
chemically similar to the sex hormones of animals
induce cell elongation and division in stem segments
Abscisic Acid (ABA)
slows growth
Seed dormancy
Primary internal signal that enables plants to withstand drought
Seed dormancy
ensures that the seed will germinate only in optimal conditions
In some seeds, dormancy is broken when ABA is removed by heavy rain, light, or prolonged cold
Precocious germination is observed in maize mutants that lack a transcription factor required for ABA to induce expression of certain genes
Primary internal signal that enables plants to withstand drought
Ethylene
Produced in response to stresses such as drought, flooding, mechanical pressure, injury, and infection
Effects of ethylene
response to mechanical stress
senescence
leaf abscission
fruit ripening
What does ethylene induce
the triple response, which allows a growing shoot to avoid obstacles
What does the triple response consist of
slowing of stem elongation
thickening of the stem
horizontal growth
Senescence
the programmed death of plant cells or organs
A burst of ethylene is associated with apoptosis
apoptosis
the programmed destruction of cells, organs, or whole plants
Leaf Abscission
A change in the balance of auxin and ethylene controls leaf abscission
Fruit ripening
triggered by a burst of ethylene production (one bad apple spoils the bunch)
