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46 terms

Biology: Chapter 39

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etiolation
plant morphological adaptations for growing in darkness
de-etiolation
changes a plant shoot undergoes in response to sunlight
phytochrome
photoreceptor that is involved in de-etiolation
second messenger
small, nonprotein, water-soluble molecule or ion, such as calcium ion or cyclic AMP, that relays a signal to a cell's interior in response to a signal received by a signal receptor protein
hormone
one of many types of circulating chemical signals that are formed in specialized cells, travel in body fluids, and act on specific target cells to change their functioning
tropism
growth response that results in the curvature of whole plant organs toward or away from stimuli owing to differential rates of cell elongation
phototropism
growth of a plant shoot toward or away from light
auxins
a class of plant hormones, including indoleacetic acid (IAA), having a variety of effects, such as phototropic response through the stimulation of cell elongation, stimulation of secondary growth, and the development of leaf traces and fruit
expansins
plant enzymes that break the crosslinks (hydrogen bonds) between cellulose microfibrils and other cell wall constituents, loosening the cell wall's fabric
cytokinins
a class of related plant hormones that retard aging and act in concert with auxin to stimulate cell division, influence the pathway of differentiation, and control apical dominance
gibberellins
a class of related plant hormones that stimulate growth in the stem and leaves, trigger the germination of seeds and breaking of bud dormancy, and stimulate fruit development with auxin
brassinosteroids
steroid hormones in plants that have a variety of effects, including cell elongation, retarding lead abscission, and promoting xylem differentiation
abscisic acid (ABA)
plant hormone that slows down growth, often antagonizing actions of growth hormones. Two of its many effects are to promote seed dormancy and facilitate drought tolerance
ethylene
The only gaseous plant hormone. Among its many effects are response to mechanical stress, programmed cell death, leaf abscission, and fruit ripening.
triple response
plant growth maneuver in response to mechanical stress, involving slowing of stem elongation, a thickening of the stem, and a curvature that causes the stem to start growing horizontally
apoptosis
changes that occur within a cell as it undergoes programmed cell death, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die
photomorphogenesis
effects of light on plant morphology
action spectrum
graph that depicts the relative effectiveness of different wavelengths of radiation in driving a particular process
blue-light photoreceptors
class of light receptors in plants; this color light initiates a variety of responses, such as phototropism and slowing of hypocotyl elongation
phytochrome
pigment involved in many responses of plants to light
circadian rhythm
physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues
photoperiodism
physiological response to photoperiod, the relative lengths of night and day; an example is flowering
short-day plant
plant that flowers (usually in late summer, fall, or winter) only when the light period is shorter than a critical length
long-day plant
plant that flowers (usually in late spring or early summer) only when the light period is longer than a critical length
day-neutral plant
plant whose flowering is not affected by photoperiod
vernalization
use of cold treatment to induce a plant to flower
florigen
flowering signal, not yet chemically identified, that may be a hormone or may be a change in relative concentrations of multiple hormones
gravitropism
response of a plant or animal to gravity
statolith
a specialized plastid that contains dense starch grains and may play a role in detecting gravity
thigmomorphogenesis
response in plants to chronic mechanical stimulation, resulting from increased ethylene production. An example is thickening stems in response to strong winds
thigmotropism
directional growth of a plant in response to touch
action potential
rapid change in the membrane potential of an excitable cell, caused by stimulus-triggered, selective opening and closing of voltage-sensitive gates in sodium and potassium ion channels
abiotic
nonliving
biotic
living
heat-shock protein
protein that helps protect other proteins during heat stress
jasmonic acid
important molecule in plant defense against herbivores
virulent
term describing a pathogen against which a plant has little specific defense
avirulent
term describing a pathogen that can only mildly harm, but not kill, the host plant
gene-for-gene recognition
widespread form of plant disease resistance involving recognition of pathogen-derived molecules by the protein products of specific plant disease resistance genes
elicitor
molecule that induces a broad type of host defense response
oligosaccharin
type of elicitor (molecule that induces a broad defense response in plants) that is derived from cellulose fragments released by cell wall damage
phytoalexin
an antibiotic, produced by plants, that destroys microorganisms or inhibits their growth
PR proteins
produces by genes that are activated by infection
hypersensitive response
plant's localized defense response to a pathogen
systematic acquired resistance
defensive response in infected plants that helps protect healthy tissue from pathogenic invasion
salicylic acid
plant hormone that may be partially responsive for activating systemic acquired resistance to pathogens