Plant Bio - Phytohormones + Guest Lectures - Quiz 4

Phytohormones are effective in..

very small amounts

What does it mean that phytohormones are produced endogenously?

they are synthesized organically by the plant from basic metabolic precursors

How do phytohormones move to the target site?

local diffusion, cytoplasmic streaming, or long-distance transport through the xylem and phloem

How do phytohormones trigger a signal transduction pathway?

non-covalent binding to a cellular protein receptor

Unlike animals, plants do not have specialized ______ ____ for hormone secretion. Hormones are produced diffuse by various cells and tissues

specialized glands

Fruit ripening, embryogenesis, seed dormancy, germination, growth and branching, flower development, fertilization and fruit formation are all regulated by…

phytohormones

_______ triggers the production of hormones to enable plants to adapt to their environment

stress

What are the steps outlining Hormone action?

Synthesis, transport, binding to receptor, signal transduction, genetic or metabolic effects (downstream effects)

What regulates hormone homeostasis within a plant?

Synthesis, conjugation, breakdown/degradation

What process can temporarily store a hormone in an inert form, lead to catabolic breakdown or lead to the active hormone’s production (once reversed)?

Conjugation

Where does hormone synthesis occur in the cell?

the cytoplasm

Deconjugation…

leads to the production of the active hormone

Hormones can move…

through xylem/phloem, across cellular membranes, through regulated transport proteins

Hormone receptors can be ______ ______ or soluble

membrane bound

Signal transduction pathways utilize reversible methods such as..

protein phosphorylation and dephosphorylation

Downstream effects of hormones can involve…

gene transcription changes and other cellular activities

Auxin regulates…

growth, embryonic patterning, root stem cell maintenance, lateral organ initiation at the shoot apical meristem, phototropism and gravitropism, branching in root and inhibit branching in the shoot, vascular development

What hormone is the only one to be transported polarly?

Auxin

When is the apical-basal axis established?

embryogenesis

What drives the apical-basal axis’ establishment?

polar, unidirectional transport of auxin

Which part of the plan is polar transport of auxin always basipetal?

shoots

Once auxin moves past the root-shoot junction the polar movement of auxin is…

acropetal

What locations of the plant have the highest amount of auxin?

shoot apical meristem (Two tunica layers L1 and L2), Root cap

Which hormone regulates lateral root initiation and development?

Auxin

Explain how Auxin regulates phototropism

Auxin accumulates on the shaded side of the plant, which causes elongation and bending towards the light source

The auxin signal that produces phototropism is a ______ signal and perceived by the shoot apical meristem

mobile

Auxin is derived from which amino acids?

Tryptophan

What is the negative gravitropism in shoots?

more auxin on the lower side promotes elongation, making shoots curve away from gravity

What is the positive gravitropism in roots?

More auxin on the lower side inhibits elongation, causing roots to curve towards gravity

What pathway produces auxin?

Trp-independent pathway

How can Auxin come into the plant cell?

the uncharged form diffuses the plasma membrane into the cell

How does charged anionic auxin come into the cell?

It enters AUX1 transporter proteins that facilitate its uptake.

How is auxin maintained in the cell?

It becomes unprotonated and cannot exit unless through PIN transporters

What controls polar auxin transport?

asymmetric distribution of auxin transporters

Where are PIN transporters located?

One side of the cell

ARF is an auxin signaling transcription _____ protein

activator

• enables transcription of auxin responsive genes

What protein inhibits the transcription of auxin responsive genes?

AUX/IAA

How is auxin signaling enabled?

Auxin binds to SCFTIR1, AUX/IAA is ubiquitinated and degraded by the 26S proteasome, ARF proteins bind and enable transcriptional activation of auxin responsive genes

Activation of auxin signaling transcription causes…

activation of proton pumps and apoplastic acidification

what membrane bound proteins are impacted by auxin, modify pH?

Proton pumps

Hormones can act like _______ ____

molecular glue

what initiates an informational relay?

Hormone binding

Which hormones regulate cell division, stem cell maintenance, auxin action, root nodule development, control of leaf senescence and nutrient allocation?

Cytokinins

Which hormone regulates the transition from meristematic stages to cell differentiation stages in the root and shoot apical meristems?

Cytokinin

What is the function of Cytokinin in the root apical meristem?

differentiation of root cells in the transition zone

What is the function of Cytokinin in the shoot apical meristem?

maintaining stem cells in shoots

What is the relationship between cytokinin and auxin?

They act antagonistically in dividing and expanding cells, production of roots and shoots

How do Cytokinin and Auxin act antagonistically at the shoot apical meristem?

Cytokinins promote stem cells, while Auxin promotes lateral organ initiation

How do Cytokinin and Auxin act antagonistically at the root apical meristem?

Cytokinin promotes differentiation at the root apical meristem while auxin maintains stem cells

How do Cytokinin and Auxin act antagonistically in the shoot?

Auxin inhibits branching in the shoot while Cytokinin promotes branching in the shoot

How do Cytokinin and Auxin act antagonistically in the root?

Auxin promotes branching in the root and cytokinin inhibits branching in the root

what are strigolactones derived from?

carotenoids, produced in roots

What hormones attract mycorrhizal fungi and promote the germination of parasitic plants (Striga)

Strigolactones

what hormones inhibit branch outgrowth?

Strigolactones

What induces strigolactone synthesis?

auxin transported from the shoot to the root and the presence of light.

Which hormone regulates growth, seed germination, flowering, sex determination and fruit growth?

Gibberellins

Mutations in which gene/enzyme results in GA deficient plants?

GA20 oxidase biosynthetic gene

What occurs in the GA signaling pathway when GA is low?

DELLA proteins inhibit growth by blocking transcription

When GA is high, what happens?

GA triggers DELLA protein proteolysis and enables transcription

What hormones regulate cell elongation, pollen tube growth, seed germination, differentiation of vascular tissues and root hairs, and stress tolerance

Brassinosteroids

Describe Brassinosteroid action in cell elongation?

loosen the cell walls, lowered resistance to internal turgor pressure

Which hormones contribute to elongation growth?

Auxins, Gibberellins, and Brassinosteroids

Which hormones contribute to branching?

Strigolactones, Cytokinins and Auxins

Hormones contribute to flower development in which ways?

patterning of floral meristem, outgrowth of organs, development of the male and female gametophytes, and cell elongation

What hormones promote cell division and growth of the fruit?

Auxin and GA

Seedless varieties of grapes and other fruits reguire exogenous _____ for fruit development

GA

Strawberry receptacles respond to….

auxin

what process initiates petal senescence, cell division, in the ovary to produce fruit and ripen it?

Pollination

Which hormone controls fruit ripening, leaf and petal senescence, cell division and cell elongation, sex determination, root growth, stress response

Ethylene

What hormone is gaseous and promotes fruit softening and flavor/color development

Ethylene

High CO2 or low O2 can limit the production of…

Ethylene

KMnO4 reaction and zeolite absorption can remove…from the air

Ethylene

What commercial plant is treated with ethylene to synchronize flowering?

Pineapple (and other bromeliads)

Which hormones are involved in sex determination?

Ethylene and gibberellins

What occurs in mutants where ethylene receptors are inhibited?

interference with fruit ripening

Plant chemistry mediates interactions between plants and…

herbivores, pollinators, microbes, and dispersers

A herbivore is defined as…

an organism that feeds on plants

Mammals and other vertebrates are usually…

generalists

Insects and other invertebrates are usually…

specialists

What are the two main strategies of plant defense against herbivores?

Resistance and tolerance

What is Resistance (Plant defense)?

Any trait that reduces the damage that a plant experiences

Low nutritional content, physical defenses, chemical defenses, and biotic defenses are…

Resistance Strategies

Regrowing following damage and maintaining reproductive output are…

tolerance strategies

Tolerance Defense Strategies are…

any traits that reduce the fitness impact of damage

What are secondary metabolites?

chemical compounds produced by plants that have no role in primary metabolism

• usually defensive or protective against herbivores, pathogens, and others.

Secondary metabolites give us…

unique flavors and medicines

What is a constitutive defense?

A defense mechanism that is always present in plants, providing constant protection against herbivores and pathogens.

What is an induced defense?

A defense mechanism that is activated or enhanced in response to herbivore attack or environmental stress, providing increased protection.

What enables plants to respond to herbivore damage?

Complex signaling pathways

What are plant biotic defenses?

Plants under attack release volatile compounds that attract predators and parasitoids of herbivores

Plants can reduce herbivore damage by causing caterpillars to…

become more cannibalistic

What are examples of plant biotic defenses?

Ant “bodyguards”, endophytic fungi, and parasitoid wasps

Positive plant-microbe interaction

nitrogen-fixing bacteria in root nodules

Negative plant-microbe interactions

apple scab on fruits and leaves that harm plant health and yield.

Neutral interaction between plants and microbes

Diverse fungal endophytes in leaves

What is becoming a new frontier for sustainable agriculture and yield improvement

Crop microbiomes

What is pollination

process by which pollen (containing the male gamete) is transferred to the femal reproductive organ of the plant

About 90% of flowering plants rely on _____ pollination

Animal

Pollinators are mosty…

Insects (especially bees) and some birds/bats

What is the driving force in diversification of angiosperms

animal pollution