plant hormones part 3 plant bio

What are the steps of signal transduction

Cell receives signal through receptor, transduces and amplifies signal, elicits response

What are common second messengers in plants

cAMP, cGMP, and Ca2+ (calcium ions)

What is a phosphorylation cascade

Addition of phosphate group to a protein catalyzes addition of phosphate to subsequent protein in pathway until final response

What are kinases

Enzymes that add phosphate groups to specific proteins

What are phosphatases

Enzymes that remove phosphate groups from proteins

What is etiolation

Morphological adaptations when flowering plant is grown in dark - includes long thin stems, small leaves, lack of chlorophyll (chlorosis)

Why does etiolation occur

Plant's attempt to reach light source by focusing energy on stem elongation and expansion

What is de-etiolation

Process when plant reaches light source - stem elongation slows, leaves expand, roots grow, chlorophyll production increases (greening)

What responds to light during de-etiolation

Phytochromes that respond to red and far-red light imbalances

Who discovered auxin

Charles Darwin (instrumental in discovery of phototropism and auxin)

What is auxin involved in

Phototropism, apical dominance, and shoot elongation

What is the main form of auxin

Indoleacetic acid (IAA) - a small polar molecule with two rings

Where is auxin produced

In the shoot tip

How is auxin transported

Downwards towards base through polar transport using PIN proteins (efflux transporters)

What is the acid growth hypothesis

As cell wall pH decreases from H+ pumping, expansins are activated, breaking hydrogen bonds and loosening cell wall, leading to cell elongation

What are expansins

Proteins activated by cell wall acidity that break hydrogen bonds and loosen cell wall

How does auxin cause phototropism

Auxins associate at shaded side, H+ is pumped decreasing pH, expansins activated, cells elongate on shaded side pushing stem toward light

What other roles does auxin have

Activating growth-related proteins, controlling branch formation, determining phyllotaxy (leaf arrangement)

What are cytokinins derived from

Adenine

Why are cytokinins named so

Due to their role in promoting cytokinesis

What is the most common naturally occurring cytokinin

Zeatin (first found in Zea mays/corn)

Where are cytokinins produced

Growing tissues like roots, fruits, and embryos

How are cytokinins transported

From roots to shoots through xylem sap

What do cytokinins regulate

Cell division, growth, and apical dominance

What is the auxin to cytokinin ratio important for

Plant growth and cell division

What happens when only cytokinins are present

Cultured plant cells cannot divide

What happens with balanced auxin and cytokinins

Cell division occurs and callus (undifferentiated parenchyma tissue) forms

What happens with higher cytokinin ratio

Cells form shoot tissue

What happens with higher auxin ratio

Cells form roots

How do cytokinins affect apical dominance

Suppress apical dominance and promote axillary bud growth (opposite of auxin and strigolactones)

What role do cytokinins play in aging

Slow plant aging - leaves stay green longer in cytokinin solution

What disease led to discovery of gibberellins

Foolish seedling disease caused by Gibberella fungus in rice

What do gibberellins primarily control

Stem elongation, fruit growth, and seed germination

Can wild-type plants grow taller with gibberellin treatment

No, they have sufficient gibberellin concentration already

What is bolting

Rapid growth of floral stalk during plant's reproductive stage

How do gibberellins affect grapes

Make them grow larger and increase internode spacing for better air circulation

What determines sex in cucurbits

High gibberellins result in male flowers, high ethylene results in female flowers

What is the gibberellin to ABA ratio important for

Determining if seed germination occurs

What is ABA's main function

Slowing down growth

Was ABA correctly named

No, originally thought to promote leaf abscission but doesn't - ethylene does

What is ABA's primary function

Seed dormancy - high ABA levels inhibit germination

What is precocious/premature germination

When ABA levels are too low and seed germinates in subpar environmental conditions

How do desert plants use ABA

High ABA levels prevent precocious germination

water washes ABA out allowing germination in moist environment

What does ABA do during drought

Closes plant stomata to reduce transpiration and prevent wilting

What makes ethylene unique among plant hormones

It is a gas hormone

What is one function of ethylene

Fruit ripening (why putting fruit in paper bag ripens them)

What is the triple response

Plant encountering barrier slows stem elongation, thickens stem, and curves horizontally

What does sudden increase in ethylene associate with

Apoptosis and senescence

What is an abscission layer

Forms at petiole from cells undergoing apoptosis, leading to leaf abscission

What actually controls leaf abscission

Ethylene (not abscisic acid)

How does ethylene relate to auxin in leaf abscission

As auxin level in leaf falls, ethylene becomes more effective and induces senescence

What happens during fruit ripening

Fruit softens, molecules converted to sugars, produces attractive scents and colors

What initiates fruit ripening

Burst of ethylene with sustained positive feedback loop

What inhibits ethylene

Carbon dioxide

What are ein mutants

Ethylene-insensitive mutants that cannot respond to ethylene and grow higher than usual (no triple response)

What are eto mutants

Ethylene-overproducing mutants that produce too much ethylene and grow shorter than usual (too much triple response)

What are ctr mutants

Constitutive triple response mutants that undergo triple response even without ethylene (very short plants)

What are brassinosteroids similar to

Molecularly similar to cholesterol in animals, functionally similar to auxin

What do brassinosteroids do

Stimulate cell elongation and division in young plant components, slow leaf abscission, promote xylem differentiation

What are jasmonates based on

Fatty acids (linolenic acid)

What is the main function of jasmonates

Plant defense (also nectar production, fruit ripening, pollen production, flowering, germination, root growth, tuber formation, mycorrhizal symbioses, tendril formation)

What are PAMPS

Pathogen-associated molecular patterns - special molecules indicating presence of pathogens

What are phytoalexins

Activated to kill pathogens

What are R genes

Resistance genes that activate specific immune responses

What is hypersensitive response

Local, specific immune response

What is systemic acquired resistance (SAR)

General defense response that spreads through entire plant

What is systemin

Initiates SAR by synthesizing jasmonic acid

What is salicylic acid

Component of SAR that spreads through entire plant prepping immune system

What are raphides

Calcium oxalate crystals in idioblasts that cut herbivore's tongue to deter herbivory

Why can humans eat most plants with raphides

Cooking destroys raphides

What do strigolactones do

Stimulate germination, control apical dominance (with auxin), regulate mycorrhizal associations

Where were strigolactones discovered from

Study of Striga plants (parasites of food-producing grains)

What are blue-light photoreceptors

Receptors that detect blue light from the sun

What are cryptochromes

Blue-light photoreceptors that inhibit stem elongation in response to blue light

What is phototropin

Blue-light receptor that controls stomatal opening and phototropism

What are phytochromes

Red (660 nm) and far-red (730 nm) photoreceptors

What are the two forms of phytochromes

Pr and Pfr

What happens when Pr receives red light

Changes to Pfr state

What happens when Pfr receives far-red light

Converts back to Pr

What does Pfr promote

Germination and horizontal growth

What does Pr promote

Inhibits germination and induces vertical growth

What is a free-running period

Plant's natural rhythm of 21-27 hours determined in constant-light environment

What resets the biological clock in plants

Sudden Pfr increase at sunrise (stimulated by red light)

What are short-day plants

Actually long-night plants - flower when night is longer than critical length

What are long-day plants

Actually short-night plants - flower when night is shorter than critical length

What are neutral-day plants

Flower no matter how long the night is

What happens if night is interrupted by red light in short-day plants

Will NOT flower

What happens if night is interrupted by red light in long-day plants

WILL flower

What flash of light matters for flowering

Only the LAST flash of light

What is vernalization

When plant is exposed to cold temperatures to induce flowering

What is positive gravitropism

Growth downwards (in gravity's direction)

What is negative gravitropism

Growth upwards (against gravity)

What are statoliths

Specialized plastids with starch inside that indicate gravity direction by sinking to bottom of cells

What is thigmotropism

Plant growth in response to touch

How do mimosa and venus flytrap respond to touch

Rapidly fold leaves through rapid loss of turgor pressure via potassium ion loss followed by water loss

What is a plant's goal during drought

Reduce transpiration

How do plants respond to drought

Alter physical structure, wilt or shed, close stomata

increase ABA synthesis

How do plants respond to flooding

Adapt to low-oxygen conditions