Chapter 39- Plant responses to internal and external signaling

Phytochrome

Which pigment in plants is primarily responsible for detecting changes in day length (photoperiod)?

There is little photoperiodic change during the year in the tropics

Why are day-neutral plants more common in the tropics than in temperate zones?

adequate; shorter; well-developed

De-etiolation has ________ light,  ________ stem, and ________ leaves. 

dark, elongated, few

Etiolation has ________ light, ________ stem, and ________ leaves.

receive; respond

Plants ________ and ________ to many signals from the environment. 

inert

Plants are not ________ or passive; they sense and integrate information from their environment. 

1. reception

2. transduction

3. response

What is the sequence of events that takes place during the plant responses to internal and external signals? (3)

reception

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

phytochrome

de-etiolation response receptor

transduction

second messengers transfer and amplify signals from receptors to response proteins

calcium ions and cyclic GMP

de-etiolation response transduction

response

leads to regulation of one or more cellular activities

greening

de-etiolation response

post-translational modification

modification of existing enzymes

phosphorylation

Post-translational modification often involves the _________ of specific amino acids. 

directly

Second messengers activate protein kinases _________ in post-translational modification. 

dephosphorylating

Protein phosphatases “switch off“ the signal transduction pathways by _________ proteins. 

transcriptional regulation

_________ _________ to increase or decrease the production of an enzyme

transcription factors

Specific _________ _________ bind directly to specific regions of DNA and control transcription of genes. 

activators

_________ increase transcription

repressors

_________ decrease transcription

plant hormones

chemical signals that modify or control one or more specific physiological processes

low

Plant hormones are produced in very _________ concentrations, but can have major effects on growth and development. 

amount; concentration

Plant hormones depend on _________ and _________ of specific hormones and often on the combination of hormones present. 

tropism

response resulting in curvature of organs toward or away from a stimulus

positive phototropism

towards light

negative phototropism

away from light

auxin

refers to any chemical that promotes cell elongation

indoleacetic acid

common plant auxin

shoot tips

Auxin is produced in _________ _________ and is transported down the stem. 

abscisic acid

slows growth, often by antagonizing the actions of growth hormones

drought

ABA has many other effects, including seed dormancy and _________ tolerance.

ethylene

produced in response to stresses such as drought, flooding, mechanical pressure, injury, and infection

triple response

Ethylene induces the _________ _________, the allowance of a growing shoot to avoid obstacles: slowing of stem elongation, thickening of stem, and horizontal growth

ethylene

Programmed cell death is triggered by an _________ burst.

ethylene burst

An _________ _________ allows the plant to break down cellular components and recycle them. 

leaf abscission

balance of ethylene to auxin controls _________ _________

auxin

Leaf abscission occurs when ethylene prevails over _________.

ripening

Burst of ethylene production in a fruit triggers the _________ process.

positive

Ethylene triggers ripening, ripening triggers release of more ethylene, making this _________ feedback. 

producers

Fruit _________ can control fruit ripening.

Light

_________ cues many key events in plant growth and development.

photomorphogenesis

effects of light on plant morphology

1. direction

2. intensity

3. wavelength

Plants detect presence of light, but also its _________, _________, and _________. 

blue-light photoreceptors

control hypocotyl elongation, stomata opening, and phototropism

phytochromes

pigments that regulate many of a plant’s responses to light throughout its life

dormant

Many seeds remain _________ until light and other conditions are near optimal. 

red

_________ light increases germination

far-red

_________ light inhibits germination

red

Leaves in the canopy absorb _________ light.

far-red (rather than red)

What type of light do shaded plants receive more?

shade avoidance

In the “_________ _________“ response, the phytochrome ratio shifts in favor of P_r, when a tree is shaded. 

day

Many plant processes oscillate during the _________. 

photoperiodism

physiological response to photoperiod

photoperiod

Plants detect the time of year based on changes in _________.

short-day plants

flower when a light period is shorter than a critical length

long-day plants

flower when a light period is longer than a certain number of hours

day-neutral plants

flowering is controlled by plant maturity, not photoperiod

gravitropism

response to gravity

positive

Roots show _________ gravitropism. 

negative

Shoots show _________ gravitropism.

statoliths

Plants may detect gravity by the settling of _________.

statoliths

dense cytoplasmic components

thigmomorphogenesis

changes in form from mechanical disturbance

thigmotropism

growth in response to touch

abiotic; biotic

Many environmental stressors, which can be _________ or _________, can have an adverse effect on survival. growth, and reproduction. 

abiotic

nonliving

biotic

living

abiotic

drought, flooding, salt stress, heat stress, and cold stress are all examples of _________ stress.

biotic

herbivores and pathogens are examples of _________ stresses. 

drought

During _________, plants reduce transpiration by closing stomata, reducing exposed surface area, and in some species, shedding leaves. 

Flooding

_________ can cause enzymatic destruction of root cortex cells to create air tubes. 

heat

Excessive _________ can denature enzymes.

evaporative cooling

Transpiration helps cool leaves by _________ _________.

Heat-shock

_________ proteins help protect other proteins from heat stress.

Cold

_________ temperatures decrease membrane fluidity.

Freezing

_________ causes ice to form in cell walls and intercellular spaces.

antifreeze

Many plants have _________ proteins that prevent ice crystals from growing and damaging cells. 

epidermis; periderm

First line of defense against infection is the barrier presented by the _________ and _________.

effectors

pathogen-encoded proteins that cripple the host’s immunity

effector-triggered

_________ immunity evolved in response to immune suppressing pathogens.

hypersensitive; systemic acquired

Effector-triggered immunity defenses include _________ response and _________ _________ response. 

hypersensitive response

causes local cell and tissue death

confine

Hypersensitive response stimulates changes in the cell wall that _________ the pathogen. 

hypersensitive response

induces production of enzymes that attack the pathogen

molecular-level defenses

production of deterrent or toxic chemicals

cellular-level defenses

cells specialized to form trichomes, store chemicals

tissue-level defenses

some leaves are toughened with sclerenchyma tissue

organ-level defenses

leaves can be modified into spines to provide mechanical defense

organismal-level defenses

may alter their physiology in response to attack by herbivores

population-level defenses

release chemicals in response to herbivore attack that trigger defense responses in other nearby plants

community-level defenses

“recruit“ predatory animals that help defend against specific herbivores