Plant Physiology Exam 4

What causes light change in the environment?

Season, weather, and habitat

What is the function of phytochromes?

Photo-receptor proteins that regulate growth

What is the function of protochlorophyllide?

precursor molecule for chlorophyll

What is the function of cryptochromes?

UV-A and blue light photoreceptors

What does phytochrome Pr do?

Absorbs red light and converts it to Pfr

What kind of reaction is the conversion of Pr to Pfr and vice-versa?

A photoconversion reaction

Which is biologically active and triggers a plant response, Pfr or Pr?

Pfr

Phytochrome synthesis

What are the proportions of Pr and Pfr during the day?

40% Pr and 60% Pfr

What is the purpose of photoconversion?

Helps plants know where they are in the environment

Where are phytochromes found?

Actively growing tissues (meristems)

What is Phytochrome A responsible for?

Responsible for etiolated form of developing shoot and hypocotyl elongation

Attributes of Phytochrome A

Functions under FR light

Phytochrome A is destroyed by light

Primary photoreceptor for sensing VLFR

What is Phytochrome B responsible for?

Responsible for stem elongation in shaded plants

Attribtues of Phytochrome B

Regulates LFR and HIR responses

Responsible for photoreversible reactions

Phytochrome C-E attributes

Less common than phyA & B

Roles still uncertain

Likely they function in a variety of processes such as shade-avoidance, elongation, expansion, and flowering

What occurs once the hypocotyl gets above ground?

FR:R drops and the plant develops

Define etiolation

Growth in the dark

What does Etiolation result in?

Lack of greening

Reduced leaf width

Leaves don’t unroll

Elongated stem

Apical hook retained

What part of the leaf does blue-light stimulate change in?

The stomata

How can the stomatal responses to blue-light be described?

Rapid, reversible, and impact the whole-plant growth dynamics

Is the response to blue-light developmentally specific?

No

What is the relationship between red and blue light in the stomata?

Blue light stimulates opening and photosynthesis, red light saturates it, and blue light again can cause a greater opening of the stomata

What plant growth responses do the genes cry1 and cry2 regulate?

Hypocotyl elongation

What plant growth responses do the genes phot1 and phot2 regulate?

Blue-light sensitivity

Are blue-light responses photoreversible?

No

What is a major similarity between cryptochromes and phytochromes?

They have apoprotein and chromophores that absorb light

What ties cryptochromes to animals and plants?

They are present in both (suggests similar evolutionary history)

Interactions among pigments

Redundancy and/or cross-talk in responses is common among photoreceptors

What is driving the gene class constans to vary

The plant’s circadian rhythm

What is regulating the gene class FT to vary

The amount of sun in a day or the “photoperiod”

Which gene class is regulating flowering?

FT expression

Why is simple little arabidopsis important?

It was the first plant to have its genome fully sequenced due to it being a “model organism”

Absisic acid plays a large role in stomatal regulation. Name another key role:

Dormancy and growth regulation

Seedling hypocotyl growth through darkness is called:

Etiolation

Downward bending foliage following ethylene exposure is called:

Epinasty

The role of phytochromes in seedling germination was discovered in which species?

Lettuce

Blue light plays an important role in guard cell opening/closing

True

What type of hormone has little transport from the site of endogenous production?

Brassinosteroids

Which scientist was one of the first to work on plant tropisms?

Charles Darwin

Which hormone type can be used to increase crop yields?

Brassinosteroids

Plant secondary metabolites have important benefits to humans, via drug discovery and pharmacological innovation

True

Which hormone class produces the triple response?

Ethylene

What is a hormone and why are they important

An organic molecule synthesized in one region of a plant and transported to other regions to create an effect. They are important as they are necessary for plant life and create drastic responses at low concentrations

When Auxin is high and cytokinin low, what tissue forms?

Root tissue

When auxin is low and cytokinin is high, what tissue forms?

Shoot tissues

I am a flower grower in Guatemala that wants to supply flowers to US supermarkets. Which hormone(s) can I use to ensure that cut flowers still have a shelf life in a location 2,000+ miles away?

Cytokinins as they delay senescence, mobilize nutrients, and are utilized in floral development

From the previous question, how can I minimize early senescence during the shipping process (what steps do I take to keeping the flowers fresh during transport)

Utilize cytokinins and minimize the production of auxin, using any other ethylene blockers available as well

Primary site of synthesis for auxin:

meristematic tissues

Primary site of synthesis for Brassinosteroids

Terpenoid pathway

Primary site of synthesis for Abscisic Acid

Nearly all plant cells (mature leaves, roots, and seeds)

Primary site of synthesis for Gibberellins

Growing shoots and seeds

Primary site of synthesis for Cytokinins

Root tissue

Primary site of synthesis for ethylene

All tissue, common in fruit

Define homeostasis

The tendency towards equilibrium between interdependent elements

True/False: Positive feedback loops maintain homeostasis

False

True/False: Negative feedbacks are important in hormone synthesis, metabolism, and catabolism

True

What are the two types of phytochromes?

Pr and Pfr

Which form of phytochrome is the" “biologically active form"?

Pfr

How are chlorophyll, phytochrome, and cryptochromes similar?

They all rely on light in some way

Are phytochromes or cryptochromes photoreversible? How do you know?

Phytochromes are photoreversible (…)

Please list 4 physiological processes mediated by phytochromes

Seed germination, etiolation, shade avoidance, …

How does a secondary metabolite vary from a primary metabolite?

Secondary metabolites are much more specialized than their counterpart and cannot occur without the primary metabolite.

Terpenes

Type example: Essential oils

Primary function: Plant defense

Phenols

Type example: Lignins

Primary function: Variety of functions; defense, support, pollinator attraction, fruit dispersion, UV light dissipation, and plant competition

N-containing organic compounds

Type example: Alkaloids

Primary function: Plant defense thru offense

Is Jasmonic acid an induced or a constitutive defense response? Please provide specific examples to defend your choice

Jasmonic acid is an induced defense response as it only activates when it is triggered. Jasmonic acid is only produced AFTER a plant lands on a venus flytrap, as an example.

What are glucosinolates matched to?

N-organic acid

What are tannins matched to?

Phenols

What are essential oils matched to?

Terpenes

What is salicylic acid matched to?

Phenols

What are alkaloids matched to?

N-organic aicds

What are phytoecdysones matched to?

Terpenes

What are cyanogenic glycosides matched to?

N-organic acids

What are flavinoids matched to?

Phenols

What are cardenolides matched to?

Terpenes

What are lignins matched to?

Phenols

What are pyrethroids matched to?

Terpenes

Permanent growth response to light

Phototropism

Rapid and reversible growth response to light

Heliotropism

Effective in pollination, defense, and carnivory

Thigmotropism

Roots exhibit negative response to light stimuli

Phototropism

Amyloplasts and statoliths used as sensors

Gravitropism

Uses a pulvinus for movement

Heliotropism

Commonly associated with vines

Thigmotropism

Auxin accumulates to inhibit growth

Phototropism

What are trichomes

Single or multiple-celled outgrowths of the epidermis, they function in absorption of water and nutrients and defend against insects by covering the leaves

What are thorns?

Modified stems