Biology 1002 Section 6: Flowering Plants: Behaviour

Altering growth and development

Plants receive signals from the environment and respond by:

signal transduction pathway

A series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response.

Reception

internal and external signals are detected by receptors, proteins that change in response to specific stimuli

Transduction

the translation of incoming sensory information into neural signals

response

Leads to regulation of one or more cellular activities. Usually responses involve increased activity of enzymes

Positive gravitropism

A growth response resulting in the curvature of roots downward

Phototropism

Growth of a plant shoot toward or away from light.

positive phototropism

growth of a plant toward light

tropism

“response”

plant hormones

chemical signally molecules that modify or control one or more specific physiological processes

Auxin

Hormones involved in plant-cell elongation, shoot and bud growth, and rooting. Also known as indolacetic acid

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.

Ethylene

plant hormone that stimulates fruits to ripen

abscisic acid

Inhibits cell growth, helps close stomata. Often considered a stress hormone

photomorphogenesis

Effects of light on plant morphology.

passage of days and seasons

Light reception allows plants to measure:

direction, intensity, wavelength

Plants detect not only presence of light but also

other properties including: (3)

blue-light photoreceptors

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

Phytochromes

A class of light receptors in plants. Mostly absorbing red light, these photoreceptors regulate many plant responses, including seed germination and shade avoidance.

far red light

inhibits germination

absorption of red light

causes Pr to change to Pfr.

Pfr

switches on physiological and developmental responses in the plant

circadian rhythm

the biological clock; regular bodily rhythms that occur on a 24-hour cycle

Photoperiod

The environmental stimulus a plant uses to detect the time of year and the relative lengths of day and night

Photoperiodism

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

long-day plants

plants that bloom only when the period of day is longer than a specific period of darkness

Short-day plants

plants that flower when nights are longer than a critical length

day-neutral plants

plants whose flowering cycle is not sensitive to periods of light and dark

Gravitropism

response of a plant to the force of gravity

positive gravitropism

growth of the roots downward, toward the earth

negative gravitropism

growth of the plant stem upward, away from the earth

Statoliths

specialized plastids containing dense starch grains, that let plants know up from down.

statolith hypothesis

Role of statoliths in sensing gravity by sinking to the bottom of cells, triggering a gravity receptor, and causing reorientation of the cell.

thigmomorphogenesis

changes in form that result from mechanical disturbance

Thigmotropism

A directional growth of a plant in response to touch.

Folds leaflets

How does Mimosa respond to touch?

drought

during _______, plants:

-reduce transpiration by closing stomata

-reduce exposed surface area

-growth of shallow roots inhibited

flooding

Oxygen deprivation during __________ causes production of ethylene that causes some cells in root cortex to undergo apoptosis. Destruction of these

cells creates air tubes that help plants survive oxygen deprivation

heat stress

can denature a plant's enzymes. Transpiration helps cool leaves by evaporative cooling.

cold stress

Decreases membrane fluidity; lipid composition of membranes is usually altered; water leaves cell in response to freezing- toxic solute concentrations in cytoplasm; many plants have antifreeze proteins

physical barrier

What is a plant's first line of defence against infection?