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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

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