Botany final

Hormones

signaling molecules

present in very low concentrations

are labile; they break down very easily

stimulate/repress cellular responses

What about hormones allows plants to change responses quickly enough?

They’re present in low concentrations and are labile

classic 5 hormones

auxin, gibberellins, cytokinins, ethylene, and abscisic acid

auxin

1st discovered hormones

made at shoot apical meristems and transported unidirectionally down the stem

regulates apical dominance

induces cell elongation during growth and cell division

stimulates fruit development if made in developing seeds (in some spp)

how does auxin regulate apical dominance?

it inhibits activity of axillary buds to maintain their dormancy

The closer the buds are to the SAM, the more repressed their growth is

because auxin is labile, the leaves further from the SAM are not getting auxin and therefore grow

keeps SAM growing more than axillary buds

How does auxin induce cell elongation?

increases acidity of apoplast, which increases enzyme activity and breaks down cell wall components

tropic responses

growth responses to a specific environmental stimulus

responses are permanent

growth is either towards the stimulus (positive) or away (negative)

phototropism

tropic growth in response to light

positive response

light breaks down auxin — plant parts in light have low auxin concentration and shaded plant parts have high auxin concentration

uneven auxin concentration results in uneven cell growth; causes a bend in the stem towards the light (plant bends on the side with high auxin concentration)

will sense presence or absence of light, how intense it is, the wavelengths, direction, and day length

endogenous

hormones made in plant’s own cells

exogenous

hormones given from outside sources (i.e., agriculture)

2,4D and 2,4,5-T

synthetic auxins

used in agent orange

Diauxin

produced from synthesis of 2,4,5-T as a byproduct

very toxic to humans

Gibberellins

hormones that induce stem elongation

works in older parts of the stem (further away from SAM)

Gibberellins in citrus plants

exogenous gibberellins decreases flower amount but increases fruit size

frequently used in commercial agriculture

in grapes, increases pedicel length and therefore allows air flow in the cluster - results in less fungal infections and rot

Cytokinins

hormones that promote cell division

discovered from adding coconut water to plant cell cultures

may delay leaf senescence (leaf aging and death)

ethylene

hormone that regulates fruit ripening in climactic plants (plants that continue ripening after being harvested, like bananas)

a hydrocarbon gas - diffused out and can affect other plants

discovered by accident

how was ethylene discovered?

Germany used a hydrocarbon gas that included ethylene for power

gas leaks would result in surrounding plants to drop their leaves (leaf abscission)

Abscisic acid

hormone that manages water-related stress

will closes stomata

manages seed dormancy

inhibits germination

nastic movements

temporary responses to environmental stimuli

slow

results from changes in turgor pressure

plant must have a pulvinus

pulvinus

structure in plants that allows nastic movements

have specialized parenchyma cells

gravitropism

tropic response to gravity

movement of amyloplasts down (are heavy, so they’re pulled down by gravity)

rely on mechanoreceptors

mechanoreceptors

receptor proteins that sense force (i.e., gravity)

when amyloplasts are pulled down onto mechanoreceptors, a signal is sent to the nucleus to change the growth habit of auxin in response to gravity

thigmotropism

tropic response to contact

ex) a tendril curling around something (positive thigmotropism)

ex) Trees growing away from wind on a beach (negative thigmotropism)

also uses mechanoreceptors

phytochrome

the photoreceptor responsible for phototropism

red light acceptor

has two parts - a protein portion and chromophore (light absorbing part)

Has a Pr form and Pfr form

Pr form of phytochrome

inactive form of phytochrome

stuck in cytoplasm

absorbs red light to become the active Pfr form

Pfr form of cytochrome

active form of phytochrome (has previously absorbed red light)

if left in the dark, converts back to the Pr form

can go into the nucleus and change gene transcription

How does phototropism work?

The phytochrome starts in the inactive Pr form in the cytoplasm

The chromophore of the phytochrome absorbs red light, converting the phytochrome to the active Pfr form

The Pfr form enters the nucleus to alter gene expression in response to the light received

skotomorphogenesis

growth responses to darkness

occurs when seedling is underground

results in etiolated phenotype

phytochrome is inactive (Pr)

etiolated phenotype

phenotype resulting from skotomorphogenesis

hypocotyl elongates

apical hook forms

cotyledons are closed, not photosynthetic, and yellow

photomorphogenesis

how a seeding develops in light

results in a de-etiolated phenotype

phytochrome is active (Pfr)

de-etiolated phenotype

results from photomorphogenesis

no apical hook; hypocotyl straightens out

hypocotyl elongation stops and growth shifts to SAM

cotyledons open and expand

cotyledons become photosynthetic and green

de-etiolation

process of shifting from etiolated to de-etiolated phenotype

shade avoidance

regulated by phytochrome

phytochrome is inactive in shade (Pr)

phenotype shifts to compete with taller plants for PAR

competition for PAR

photosynthetically active radiation

400-700 nm wavelengths

absorbed most by tall plants; when it reaches the plants beneath them, most useable light has been absorbed already

leaves low-quality light for plants shaded by others

results in shade-avoidance phenotype

shade-avoidance phenotype

elongated stem

fewer/smaller leaves

more yellow in pigment

produces flowers as a last ditch effort to reproduce and spread genes to a better environment

photoperiodism

flowering in response to length of day and night

short day plants

need long nights and short days

when night starts, they start timing the length of night and will only bloom if it’s been dark for long enough

evolved in temperate envs

long day plants

need long days and short nights to bloom

evolved in temperate envs

day intermediate plants

day and night must be relatively equal to bloom

evolved in tropics

day neutral plants

do not flower in response to day length

evolved in tropics

vernalization

flowering in response to low temperature

use temperature-sensitive protein receptors

usually biennial plants (live for 2 years) - 1st year is just vegetative growth, then winter signals for reproductive growth in the 2nd year

Primary metabolties

reauired by an organism for normal growth and development

secondary metabolites

not required by an organism, but advantageous

are grouped based on biosynthetic pathways

alkaloids, terpenes, and phenolics

alkaloids

nitrogen containing secondary metabolites

morphine, capsaicin, caffeine/theobromine

morphine

alkaloid

only made by Papaver somniferum species

most concentrated in the fruit

produced as a latex

used in planta as antiherbivory - causes animals to feel unwell if eaten

used by humans as a pain killer (strongest pain killer)

how does morphine work as a pain killer?

works as an endorphin analog (endorphin = feel good chemical)

morphine binds to opiate receptors on animal nerves

normally, GABA is released from nerve 1 and binds to another - prevents dopamine release

with morphine, opiate binds to nerve 1 and inhibits release of GABA - dopamine release no longer inhibited

COD = suppression of nervous system results in loss of breathing, heart rate, brain fxn, etc

Capsaicin

alkaloid

found only in the pepper genus Capsicum

made in the fruit

in planta fxn: antiherbivory (spicy) and protection against fungal infection

birds are not affected but mammals are

Proposed explanation for why birds are not affected by capsaicin?

selection of specific seed dispersers

birds don’t have teeth - seeds pass through bird intact and are more likely to successfully germinate after

scoville scale

measures spiciness of peppers by measuring the amount of capsaicin in them

capsaicin synthase

gene that makes capsaicin

capsaicin mechanism of action

binds to TRPV1 sensory receptor on sensory neurons

TRPV1 is usually activated around 37-45 C

binding of capsaicin changes shape of TRPV1 - activates it without a temperature change

Why doesn’t drinking water alleviate spiciness?

capsaicin is hydrophobic; water does not bind to it

milk (lipids) are also hydrophobic and should be used instead

capsaicin medicinal uses

relieves arthritis pain by binding receptors and stimulating heat

used to treat chronic pain, but we odn’t really know why - hypothesis is that exposure to capsaicin overloads nerves and stops their communication

caffeine/theobromine

alkaloids

very closely related

produced by over 60 species

in planta fxn = antiherbivory (tastes bad) and allelopathy (caffeine released in soil prevents other plant seeds from germinating)

affects all animals with nervous systems

Main species that produce caffeine

Coffea arabica (coffee from seeds)

Camellia sinensis (tea from young leaves)

Main species that produce theobromine

Theobroma cacao (chocolate from seeds)

caffeine/theobromine mechanism of action

stimulates CNS

relaxes smooth muscles (intestines)

Terpenes

made from the precursor molecule isopentenyl pyrophosphate (IPP)

menthol, taxol, beta-carotene, rubber

menthol

terpene

produced by Mentha genus plants - mints/aromatic plants

made in glandular trichomes

in planta fxn = antiherbivory (smells foul to other animals)

a volatile compound that is released into the air when trichomes are broken

used for mint flavoring

menthol medicinal properties

has a cooling effect - binds to sensory receptor TRPM8 that normally activates at less than 20 C and sends the “cold” signal

used for sinus relief

Taxol

terpene

produced only by the Taxus brevifolia species

made in cambium of tree

in planta fxn = antifungal properties

human use = chemotherapy

How is taxol used in chemotherapy?

It is a mitotic inhibitor that stops cell division

stabilizes MTs during metaphase to prevent them from disassembling and pulling chromosomes apart - prevents anaphase

also prevents chromosomes from attaching to mitotic spindles

causes cell apoptosis

beta-carotene

a terpene

carotenoid pigment found in all plants (secondary metabolite status debated; is photosynthetic)

colors fruits and flowers red, orange, and yellow

in planta fxn = herbivore and pollinator attraction

human use = nutrient dense foods

beta-carotene nutrients

is a vitamin A precursor - why carrots improve vision

act as antioxidants - prevents oxidation and damage from reactive oxygen species produced during cellular respiration

How is beta-carotene responsible for some animals’ coloration?

beta-carotene structure is stable through the food chain due to its hydrophobicity

pigments survive being passed down the food chain and affect pigmentation of organism eating them

ex) photosynthetic plankton turn the shrimp that eat them pink, and in turn the flamingoes that eat the shrimp also turn pink

Rubber

Terpene

made only by the Hevea brasiliensis species (rubber tree)

derived from plant-produced latex

made in cambium

in planta fxn = antiherbivory

human use = rubber

can be harvested sustainably

history of the first human use of rubber

mesoamerican natives formed rubber into balls to play hip-ball

1st team sport in history

losers were decapitated

phenolics

derived from the aa phenylalanine

anthocyanins, flavenoids, cannabinoids

anthocyanins

phenolics

in many plants

blue/purple/pink pigments that are water-soluble and stored in vacuoles

pH sensitive

in plants fxns = attraction and protection against sun damage

human use = food coloring, antioxidants

Flavenoids

phenolics

produced by Glycine max species - soybeans

in planta fxns = communicating with rhizobia and antioxidants associated with seeds

human use = phytoestrogens

phytoestrogens

analogs of estrogen

produced by soybeans

daidzein and genistein compounds - when eaten, they are converted into equol

equol binds to estrogen receptors

used in birth control and HRT

cannabinoids

half terpene, half phenolic

produced by Cannabis genus plants

made in glandular trichomes - most abundant on female flowers (to protect next gen)

in plants fxns = antiherbivory and UV protection (plants at higher elevations produce more)

human uses = hemp fibers for cloth, medicinal uses, recreational drugs

most concentrated strains = CBD and THC

THC-A

psychoactive strain of a cannabinoid

affects the endocannabinoid signaling system

medicinal uses = pain regulation and appetite stimulant for chemo patiens

endocannabinoid signaling system

uses CB1 and CB2 receptors

found in brain but NOT brain stem - lack of receptors in brain stem makes ODing less likely

THC binds to CB1 and CB2 receptors instead of the endogenous ligands - regulates appetite, metabolism, pain sensation, memory, etc

THC binds to regulators that affect brain = psychoactive

CBD

concentrated cannabinoid strain

not psychoactive - does NOT binds regulators that affect brain

medicinal uses = lessens seizures (epilepsy treatment), antianxiety, antinausea, and antibiotic against MRSA strains

genetic modifications version 1

selectively breeding for traits favorable for agriculture

done with plants and animals for thousands of years

genetic modifications version 2

hybridization - crossing 2 spp to make a hybrid plant

merging genomes

genetic modifications version 3

mutagenesis - modifying DNA sequences via mutations

uses chemicals or radiation

a random process that can’t be controlled

genetic modifications version 4

genetic engineering

high specificity - can be controlled

much faster process

via horizontal gene transfer

vertical gene transfer

parents pass genes to offspring

horizontal gene transfer

transfer of genetic info from 2 unrelated individuals

allows transfer of genes between completely unrelated plants (and plants and animals)

GMO process

1. isolate gene of interest

2. create recombinant DNA molecule (rDNA)

3. insert rDNA into bacteria for amplification

4. insert amplified rDNA into plant cell

5. test transgenic plant

Isolate gene of interest

GMO step 1

uses restriction enzymes that recognize and cut up target sequences

then uses electrophoresis to separate target DNA from other DNA sequences

Create recombinant DNA molecule

GMO step 2

occurs simultaneously to step 1

restriction enzymes produce sticky ends on cut DNA strands - homologous sequences on two separate strands bind

resulting rDNA will also have an ampr gene - an antibiotic resistance gene on plasmids

insert rDNA into bacteria for amplification

GMO step 3

requires bacterial transformation that occurs via heat shock (sudden heat changes destabilizes bacteria membranes, rDNA just flows in)

resulting bacteria are plated on agar with ampicillin - bacteria without the ampr gene did not transform and therefore die

insert DNA into plant cell

GMO step 4

rDNA is extracted from bacteria and inserted into plant cells via biolistics or the Agrobacterium tumefaciens species

Using Agrobacterium tumefaciens to insert rDNA into plant cells

the preferred method

a naturally occurring soil bacteria that infects plants

causes tumors

uses horizontal gene transfer

inserts a gene for synthesis of a cytokinin analog - promotes cell division

inserts genes for synthesis of opines - carbs that can’t be metabolized by the plant = food for bacteria

scientists replace those 2 genes with the rDNA via heat shock - agro bacteria then inserts the rDNA instead of the original genes

Using biolistics for inserting rDNA into plant cells

uses a “gene” gun that shoots particles coated in rDNA into a plant

particle goes through the plant, rDNA stays behind and is incorporated into cell genome

last resort, not as affective

inserts many gene copies - too many may prevent the gene from being expressed

may insert the gene in telomeres - gene will be unexpressed

testing transgenic plant

GMO step 5

insert resistance to herbicide with gene of interest

cells that transformed successfully will survive on agar plated with herbicide

use hormones to direct plant cells to divide and differentiate into SAMs, RAMs, leaves, etc

test new plant for target gene via PCR

Flavr Savr tomato

1st gmo plant to become available on the market

produced because non-GMA tomatoes bruise and rot easily during transport

get soft as they ripen as cell walls break down

Flavr savr tomatoes were modified so they had less enzymes that broke down cell walls (gene was silenced)

Bt corn

1st successful GMO plant

corn is very susceptible to corn borers

Bt corn was modified to contain the para-sporal crystal gene from Bacillus thurengiensis

Bacillus thurengiensis

spore-forming bacteria with genes used to modify corn

spore wall forms for hibernation when bacteria is stressed

forms a para-sporal crystal (a protein that senses when conditions improve for the bacteria) on the spore wall exterior

good conditions = inside caterpillars (food source for bacteria)

spores were sprinkled on plants as a form of pesticide

gene for the para-sporal crystal was inserted into the Bt corn genome - when a caterpillar eats the modified leaves, they die

Ht crops

herbicide tolerant

plants with genes that allow resistance to glyphosate herbicide

allows crops to be sprayed with weed-killing herbicide (competition reduction)

glyphosate pros

non-toxic to animals

binds to soil (does not leak into watershed)

short half-life (gets broken down by microorganisms)

glyphosate cons

allegedly causes cancer - those that get cancer are people that handle it in very large quantities every single day

company that sells it will not let farmers collect seed from their Ht crops to reuse them

Papaya

commonly modified via vaccine to protect against papaya ringspot virus (PRSV)

used a gene for the virus’ coat protein in the rDNA used

viral coat protein sequences were inverted so that they were homologous to each other - formed a hair pin loop

anytime a similar sequence to the ds RNA is detected, it is degraded

ds RNA triggers an immune response and antibodies recognize from then on

arctic apples

GMO apples that don’t brown

in normal apples, browning is caused by the polyphenol oxidase enzyme

the enzyme is removed in arctic apples (used rDNA of its own gene to form ds RNA that triggers an immune response against the gene for that enzyme)

decreases food waste

innate potatoes

GMO potatoes modified to prevent bruising (gene responsible for browning is silenced)

prevents food and resource waste

also modified to have low levels of asparagine which reacts with sugar at high temperatures to produce acrylamide - a carcinogen and neuro toxin

resistant to potato blight

pink pineapples

GMO pineapples

turned pink for aesthetics

modified pigment production pathways

purple tomatoes

GMO tomatoes

alters pigment production pathway by adding anthocyanin genes

inserted snapdragon genes

increases antioxidants

increases shelf-life by 30%