Bio 104 — Chapter 26

What stimuli do plants respond to and what do these responses lead to?

Light, gravity, CO2 levels, pathogens, drought, and touch; these responses lead to survival

What are short-term and long-term plant responses?

Short-term: stomata open and close; Long-term: response to gravity

How do roots and stems grow in response to gravity?

Roots grow downward; stems grow upward

What is signal transduction and what are its three main parts?

Binding of molecular signal initiates response; receptors, transduction pathway, cellular response

What are receptors and transduction pathways?

Receptors are proteins activated by a signal; transduction pathways are proteins (enzymes) that transform the signal

What do hormones enable plant cells to do and where are they synthesized?

Enable plant cells to communicate; synthesized in one part of the plant

What are the five major plant hormones?

Auxins, gibberellins, cytokinins, abscisic acid, ethylene

Where are auxins produced and where are they found?

Produced in the shoot apical meristem; found in young leaves, flowers, and fruits

What is apical dominance and how do auxins affect roots, fruits, and leaves?

Auxin prevents growth of axillary buds; promotes growth of roots and fruits; prevents loss of leaves and fruits

How do auxins cause stems to bend?

Auxin moves to the shady side, activates proton pumps, loosens cell walls, increases turgor pressure, and causes cell elongation

What are gibberellins and what do they cause?

Growth-promoting hormones that cause stem elongation

What is the most common gibberellin?

Gibberellic acid

What do cytokinins promote, where are they found, and what do they prevent?

Promote cell division; found in dividing tissues of roots, seeds, and fruits; prevent senescence

What is abscisic acid (ABA) and what are its effects?

A stress hormone; growth inhibitor; maintains seed and bud dormancy; causes stomatal closure

What is ethylene and what are its effects on plants?

A gas formed from amino acid methionine; causes abscission and fruit ripening

What is abscission?

Dropping of leaves, fruits, and flowers

What is a tropism and what are positive and negative tropisms?

Growth toward or away from a unidirectional stimulus; positive toward, negative away

What is gravitropism and what structures and hormones are involved?

Movement in response to gravity; involves statoliths and auxin

What is phototropism and what causes it?

Movement in response to light; auxin causes cells on shady side to elongate; blue-light pigment initiates response

What is thigmotropism and thigmomorphogenesis?

Growth due to contact with solid objects; entire plant responds to stimuli like wind and rain

What are nastic movements and how do they differ from tropisms?

Movements not involving growth and not dependent on stimulus direction

What causes turgor movements and give examples?

Touch, shaking, or thermal stimulation; Mimosa pudica and Venus flytrap

What are sleep movements and circadian rhythms?

Daily movements responding to light and dark; circadian rhythms occur within 24 hours and persist without stimulus

What is photoperiodism and what pigment is involved?

Response to changes in day and night length; phytochrome

What are the two forms of phytochrome and their activity states?

Pr is inactive; Pfr is active

What plant processes involve phytochrome?

Seed germination, stem elongation, flowering

What are short-day, long-day, and day-neutral plants?

Short-day flower when day length is shorter than critical; long-day when longer; day-neutral not dependent on day length

What physical defenses do plants have?

Cuticle-covered epidermis and bark

What are secondary metabolites and give examples?

Plant defense chemicals; tannins, alkaloids, cyanogenic glycosides

What is the hypersensitive response (HR)?

Wound response that seals the wounded area

What are proteinase inhibitors and systemin?

Chemicals and signals involved in wound response that disrupt herbivore digestion

What hormones are involved in plant wound responses?

Salicylic acid and jasmonic acid