Chapter 39 - Plant Responses to Internal and External Signals

Question 1

etiolation

Answer 1

Plant morphological adaptations for growing in darkness.

Question 2

de-etiolation

Answer 2

The changes a plant shoot undergoes in response to sunlight; also known informally as greening.

Question 3

second messenger

Answer 3

A small, nonprotein, water-soluble molecule or ion, such as a calcium ion (Ca2+) or cyclic AMP, that relays a signal to a cell’s interior in response to a signaling molecule bound by a signal receptor protein.

Question 4

hormone

Answer 4

In multicellular organisms, one of many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the body, changing the target cells’ functioning. Hormones are thus important in long-distance signaling.

Question 5

tropism

Answer 5

A growth response that results in the curvature of whole plant organism toward or away from stimuli due to differential rates of cell elongation.

Question 6

phototropism

Answer 6

Growth of a plant shoot toward or away from light.

Question 7

auxin

Answer 7

A term that primarily refers to indoleacetic acid (IAA), a natural plant hormone that has a variety of effects, including cell elongation, root formation, secondary growth, and fruit growth.

Question 8

expansin

Answer 8

Plant enzyme that breaks the cross-links (hydrogen bonds) between cellulose microfibrils and other cell wall constituents, loosening the wall’s fabric.

Question 9

cytokinin

Answer 9

Any of 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.

Question 10

apoptosis

Answer 10

A type of programmed cell death, which is brought about by activation of enzymes that break down many chemical components of the cell.

Question 11

gibberellin

Answer 11

Any of 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 (with auxin) stimulate fruit development.

Question 12

brassinosteroid

Answer 12

A steroid hormone in plants that has a variety of effects, including inducing cell elongation, retarding leaf abscission, and promoting xylem differentiation.

Question 13

abscisic acid (ABA)

Answer 13

A plant hormone that slows growth, often antagonizing the actions of growth hormones. Two of its many effects are to promote seed dormancy and facilitate drought tolerance.

Question 14

strigolactones

Answer 14

A class of plant hormone that inhibits shoot branching, triggers the germination of parasitic plant seeds, and stimulates the association of plant roots with mycorrhizal fungi.

Question 15

ethylene

Answer 15

A gaseous plant hormone involved in responses to mechanical stress, programmed cell death, leaf abscission, and fruit ripening.

Question 16

triple response

Answer 16

A plant growth maneuver in response to mechanical stress, involving slowing of stem elongation, thickening of the stem ,and a curvature that causes the stem to start growing horizontally.

Question 17

photomorphogenesis

Answer 17

Effects of light on plant morphology.

Question 18

action spectrum

Answer 18

A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process.

Question 19

blue-light photoreceptors

Answer 19

A type of light receptor in plants that initiates a variety of responses, such as phototropism and slowing of hypocotyl elongation.

Question 20

phytochrome

Answer 20

A type of light receptor in plants that mostly absorbs red light and regulates many plant responses, such as seed germination and shade avoidance.

Question 21

circadian rhythm

Answer 21

A physiological cycle of about 24 hours that persists even in the absence of external cues.

Question 22

photoperiodism

Answer 22

A physiological response to photoperiod, the relative lengths of night and day. An example of photoperiodism is flowering.

Question 23

short-day plant

Answer 23

A plant that flowers (usually in late summer, fall, or winter) only when the light period is shorter than a critical length.

Question 24

long-day plant

Answer 24

A plant that flowers (usually in late sprint or early summer) only when the light period is longer than a critical length.

Question 25

day-neutral plant

Answer 25

A plant in which flower formation is not controlled by photoperiod or day length.

Question 26

vernalization

Answer 26

The use of cold treatment to induce a plant to flower.

Question 27

florigen

Answer 27

A flowering signal, probably a protein, that is made in leaves under certain conditions and that travels to the shoot apical meristems, inducing them to switch from vegetative to reproductive growth.

Question 28

virulent

Answer 28

Describing a pathogen against which an organism has little specific defense.

Question 29

avirulent

Answer 29

Describing a pathogen that can mildly harm, but not kill, the host.

Question 30

gene-for-gene recognition

Answer 30

A widespread form of plant disease resistance involving recognition of pathogen-derived molecules by the protein products of specific plant disease resistance genes.

Question 31

hypersensitive response

Answer 31

A plant’s localized defense response to a pathogen, involving the death of cells around the site of infection.

Question 32

systemic acquired resistance

Answer 32

A defensive response in infected plants that helps protect healthy tissue from pathogenic invasion.

Question 33

salicylic acid

Answer 33

A signaling molecule in plants that may be partially responsible for activating systemic acquired resistance to pathogens.