Chapter 39 Flashcards
Etiolation
Physical adaptations for growing in darkness
De-etiolation
After exposure to light, plant greens meaning the shoots and roots grow normally again
Different ways that plants can detect light
Intensity, spectral composition, direction it’s coming from, spatial gradient of intensity, amount of time it’s available
Photomorphogenesis
Effects of light on plant morphology
Two different classes of light receptors
Blue-light photoreceptors, phytochromes
Blue-light photoreceptors
Absorb blue light
What plant responses does blue light initiate?
Hypocotyl elongation, stomata opening, phototropism
Cryptochromes
Blue-light receptors involved in inhibition of stem elongation
Phototropin
Protein kinase involved in mediating blue-light-mediated stomatal opening, chloroplast movements, and phototropic curvatures
Phytochromes
Pigments that absorb mostly red and far-red light ; red light increases germination, far-red light inhibits germination
Responses to Pfr
Seed germination ; inhibition of vertical growth and stimulation of branching ; setting internal clocks ; control of flowering
What does red light trigger verse far-red light
Red light converts Pr to Pfr ; far-red light converts Pfr to Pr
Shade avoidance response
When a tree is shaded, the phytochrome ratio shifts in favor of Pr inducing vertical growth
Photoperiodism
The environmental stimulus plants use most often to detect the time of year
Gravity
A constant force and critical environmental cue for plants to determine the growth pattern
Gravitropism
Response to gravity ; roots show positive gravitropism (grow down) ; shoots show negative gravitropism (grow up)
How can plants detect gravity?
By the settling of statoliths, which are dense cytoplasmic components
Thigmomorphogenesis
Refers to changed in form that result from mechanical disturbance ; growth in response to touch
Action potentials
Transmission of electrical impulses
Phytotoxins
Metabolites (bioproducts) produced by plant pathogens to damage the cell plants ; affect photosynthesis, germination, and root and shoot growth
Eavesdropping
Chemical defense signals can be detected by eavesdropping neighbors and used to prime their own defenses ; targeted to other branches of the same plant or to insect bodyguards
Plant hormones
May act via signaling by removing a repress or from a transcription factor that stimulates the expression of growth-promoting genes
Ubiguitin
Protein that binds covalently to another protein and targets it for breakdown
What are some example of things Auxin does?
(Indole-3 acetic acid) root initiation ; leaf and fruit abscission ; apical dominance ; fruit development ; cell expansion
What does Auxin do?
Inhibits growth of the axillary buds further down on the stem to promote apical dominance
Charles Darwin and his son Francis
Observed positive phototropism in grass seedlings only if the tip of coleoptile was present and exposed to light ; postulated that a signal was transmitted from the tip to the elongating region
Auxin protein pumps
Can set up concentration gradients of auxin in plant tissue
Case study of Auxin
Cells at coleoptile tip sense light, hormone travels from tip down the coleoptile, cells lower in coleoptile respond to hormone ; bending results
Loosening of the cell wall and enabling elongation
Actin increases activity of proton pumps, low pH activated expansions, polysaccharides are cleaved by cell wall-loosening enzymes, losening the microfibrils
Some of the effects of gibberellins
Stem elongation, fruit growth, seed germination
What does Abscisic acid (ABA) do?
Slows growth, often by antagonizing the actions of growth hormones ; Has many effects on plants including seed dormancy, drought tolerance, causes stomata to rapidly close, and it can act as an “early warning system”
When is Ethylene produced?
When a seedling tip pushes against an obstacle ; it induces a triple response in which stem elongation is slowed, the stem thickens and then begins to grow horizontally ; vertical growth resumes when ethylene wears off
Senescence
Programmed cell death of certain cells or organs or entire plants
What is a burst of ethylene associated with?
Apoptosis
Abscission
Process that occurs in autumn when a leaf falls ; change in the balance of auxin and ethylene controls this
Burst of ethylene production in fruit
Triggers ripening, and reopening tiggers release of more ethylene
What do brassinosteroids do?
They induce cell elongation and division in stem segments and seedlings at low concentration ; slow leaf abscission and promote xylem differentiation
What does physical wounding of plants do?
Causes a rapid loss of hydrostatic pressure and generated electrical perturbation called variation potential to travel a short distance beyond the wound through the xylem
What are jasmonates?
Produced in response to wounding and are involved in controlling plant defenses ; activate the wound response genes that code for the production of a second round off wound-induced chemical defenses
What is systemin and what does it do?
It is a wound-response hormone produced by herbivore-damaged cells initiatives a protective response ; synthesis of jasmonic acid in undamaged cells activated the production of proteinase inhibitors
Pheromones
Chemical messengers synthesized by an individual and released into he environment that elicit a response from a different individual ; plants produce wasp attractant pheromones in response to attack by caterpillars
Some other things that Jasmonates does?
Nectar secretion, fruit ripening, pollen production, flowering time, seed germination, root growth, tuber formation, mycorrhizal symbiosis, tendril coiling
Abiotic stress
Drought, flooding, salt stress, heat stress, and cold stress ; during drought plants reduce transpiration by closing stomata, reducing exposed surface area and in some species, shedding leaves
Biotic stresses
Herbivores and pathogens ; plants use defense systems to deter herbivory, prevent infection, and combat pathogens
