PLANT GROWTH AND DEVELOPMENT

1
PLANT GROWTH AND DEVELOPMENT

• General Features
• Cellular Basis of Plant Growth
• Developmental (Growth) Responses to Environment
• Photoreceptors
• Signal Transduction Mechanisms
• Developmental Responses to Plant Hormones
• Auxins
• Cytokinins
• Gibberellins
• Abscisic Acid
• Ethylene
• Other Plant Hormones

2
TERMINOLOGY
Growth irreversible increase in mass involves
cell division cell enlargement/expansion Differ
entiation change from generalized cell type to
specialized one with specific functions - are
50 different types of plant cells Development
Growth Differentiation Morphogenesis the
development of form/shape cell, organ, entire
plant depends what talking about e.g., leaf
primordia
3
PLANT GROWTH
1. Localized, Arithmetic Growth (copy error rate
high?) 2. Open Growth continue to initiate new
organs (roots, stems, leaves) throughout
lifespan 3. Indeterminate Growth many continue
to grow throughout lifespan 4. Cell
differentiation is readily reversible
Totipotency single differentiated cell can
de-differentiate, behave like zygote and give
rise to whole new plant!
4
Cloning Plants
F.C. Steward (1950s) carrot root phloem cells
can behave like zygotes! regenerate whole fertile
carrot plants genetically identical to original
one! tissue culture callus mass of
undifferentiated cells - can propagate it
forever! (like HeLa cancer cells)
differentiated cells ? callus ? form roots/shoots
? entire plantlet (presence of plant growth
hormones)
5
Cloning Plants
some plants produce plantlets themselves clones!
fern plantlets on leaves
Kalanchoe plantlets on leaf margins
6
VALUE OF TISSUE CULTURE

• propagate individual plants while maintaining
  desirable traits/genomes (orchids, etc.)
• 2. develop new genotypes with desired traits
  genetic engineering (cloning)
• 3. study genetics of somatic cells (instead of
  germ cells)
• IMMORTALITY?

some plants become very old bristlecone pines
in Southern California 5,000 years old!
worlds oldest living organism
7
IMMORTALITY when is a plant dead?
Redwood Trees oldest 2,000 years old
Cypress Trees oldest 1,500 years old
8
CELLULAR BASIS OF PLANT GROWTH cell division,
enlargement differentiation done in different
parts of plant
axillary bud pocket of meristematic cells left
behind (also vascular cambium) remain
undifferentiated
Zone of cell division Meristem (shoot root
apical meristems)
Zone of cell elongation ( some
differentiation!)
Cell differentiation mostly further away from
apical meristem lot of overlap not sharply
demarcated
9
CELL DIVISION The Cell Cycle ( phases of DNA
synthesis and division)
S
G1
G0
G2
interphase
M
some plant growth hormones stimulate cell
division (e.g., cytokinins) causing them to
break dormancy and re-enter cell cycle
10
CELL EXPANSION/ENLARGEMENT Turgor
Pressure (osmotic properties are driving force
for plant cell growth)
central vacuole
H ions (protons) pumped into cell wall by
H-ATPases (?pH) 1. weakens interactions
between wall components (pectins,
cellulose, etc.) 2. stimulates expansins
(proteins involved in wall loosening)
some plant growth hormones stimulate cell
enlargement or elongation (e.g., auxins)
11
CELL DIFFERENTIATION
occurs after cell division (and
enlargement/elongation) so it keeps
progenitor-type cell (meristem) intact
meristematic cell maintained
meristematic cell
(arithmetic growth)
protoderm cell
epidermal cell
12
CELL DIFFERENTIATION
cell division itself CAN be involved in
differentiation
trichome initial
asymmetric cell division
elongate epidermal cell
13
DIFFERENTIATION GENETIC BASIS
study gene expression during differentiation ce
rtain genes up-regulated, others
down-regulated some genes are specific for
development also! involves temporal (time)
spatial (space) regulation of gene
expression changes in gene expression must by
highly coordinated among genes 1. maintain
proper function in cells/tissues 2. form
complex cellular structures (pts. apparatus,
mitotic spindle, etc.)
Patterns of Gene Expression SPATIAL 1.
every cell type (housekeeping genes) 2.
cell-specific 3. tissue-specific 4.
organ-specific TEMPORAL 1. constituitive
on all the time 2. regulated/modulated
a. inducible b. repressible c. rhythmic
(e.g., circadian day/night, on 24-hour clock)
14
DIFFERENTIATION GENE EXPRESSION
molecular cloning of genes
permitted initial studies of individual gene
expression provided sequences and
probes/tools for such studies
15
DIFFERENTIATION GENE EXPRESSION
now know that developmental regulation of genes
occurs at 1. transcription almost always
2. mRNA stability/degradation 3. translation
4. protein stability/degradation 5.
posttranslational modification (phosphorylation,
etc.) How study gene expression?
Northern Blots Nuclease Protection Assay
Microarrays, etc.
(-)
()
gel
16
GENE EXPRESSION
MICROARRAYS permit genome-wide gene expression
studies EVERY GENE! if know all/most of
possible genes that exist for a plant -
get this from whole-genome sequencing 2009 -
140 eukaryotes in GenBank 30 in JGI or
from expressed sequence tags (ESTs) mRNA? cDNA
? clone partially sequence ? identify by
many of them sequence
homology
17
MICROARRAY
separately spot single-stranded DNA for each gene
on microscope slides (1,000s) or computer
chips ideally want to know which gene each spot
encodes
18
mRNA
make cDNA and incorporate fluorescently-labeled
nucleotides
digest RNA to generate single-stranded cDNAs
hybridize to microarray
wash away unbound DNAs
Gene A Gene B Gene C Gene D
MICROARRAY
therefore, Genes A B were being expressed when
isolated mRNA Genes C D were not being
expressed when isolated mRNA
19
root parenchyma mRNA
leaf mesophyll mRNA
most expressed genes are not involved in
development
Gene A Gene B Gene C Gene D
only Gene B expressed in both cell types
candidate for developmental gene?
20
MICROARRAYS
slide
chip
intensity of fluorescence proportional to amount
of mRNA!
21
MICROARRAY DATA
What kinds of data do you get from these
studies? e.g., tobacco (Nicotiana tabacum)
- has 106 kb of DNA/nucleus estimate
average gene/mRNA 1 kb, so 106 genes in
total leaf mRNA - 30,000 genes expressed -
most NOT developmental ones if compared another
organ, might find that 10,000 genes in common
many of these may represent genes involved in
development
may be 8,000-10,000 genes that are organ-specific
(e.g., leaf) but organs contain MANY kinds of
cells improved technology - can look at mRNA from
few cells- all one type - amplify mRNA and
proceed w/probing microarray deep sequencing
cDNAs directly more sensitive get precise
numbers of mRNAs in cells/tissues examined
22

• STRATEGY for finding key regulatory genes in
  development genetic approach
• identify/isolate developmental mutants of a model
  genetic organism
• 2. map and clone the gene
• 3. study genes structure and function

Arabidopsis thaliana
Zea mays (corn)
23
HOMEOTIC GENES control overall body plan of an
organism have common homeobox sequences (180
bp) transcribed/translated into homeodomains
in proteins DNA-binding domains act as
transcription factors mutations can lead to
very bizarre-looking organisms (e.g.,
antennapedia mutant in fruitfly)
homeodomain of protein (red)
homeobox sequence of DNA
fruitfly face bearing extra legs instead of
antennae
24
Arabidopsis thaliana (mustard family) model
plant system small organism short reproductive
cycle n 5 (chromosomes) smallest known genome
of angiosperms (flowering plants)
in plants, homeotic genes determine organ
identity - so mutants have one organ
transformed into another!
25
FLOWER DEVELOPMENT
flower modified shoot system floral parts
modified leaves shoot apical meristem produces
primordia giving rise to 4 whorls in order 1)
sepals, 2) petals, 3) stamens, 4) carpels
(pistils) plant differentially expresses 3
classes of homeotic genes (A,B,C)
class A
class B
class C
26
FLOWER DEVELOPMENT
expression of gene classes in primordia of four
different whorls of floral parts
27
FLOWER DEVELOPMENT
Class B mutant (B not expressed)
X
wild-type
B mutant
28
Gene Class B mutant (B is not expressed)
2 outer whorls sepals (A only) 2 inner whorls
carpels (C only)
what would mutant in C produce?
29
Gene Class C mutant (C is not expressed)
Note A C are mutually antagonistic so if one
not expressed, the other is expressed
X
wild-type
C mutant
30
Gene Class C mutant (C is not expressed)
all sepals and petals!
31
Triple mutant (A, B C)
all 3 activities missing produces only leaves!
32
DEVELOPMENTAL RESPONSES TO THE ENVIRONMENT
no complex sensory organs cant run away
responses simpler/slower - are coordinated
growth and differentiation in response to the
environment external light, water, gravity,
nutrients, touch, etc. internal plant hormones,
enzymes, various chemicals cell-cell
contacts (positional effects) (location
determines what a cell will become!)
environmental signals/stimuli elicit responses
through signal transduction mechanisms

• VERNALIZATION need prolonged cold period for
  seed germination or flowering
• - relates to seasons of year

cabbage (biennial) on left in greenhouse for 5
years - never exposed to winter conditions it
needs to flower so never flowered! - younger
one on right is flowering
33
DEVELOPMENTAL RESPONSES TO THE ENVIRONMENT
2. GRAVITY roots grow toward earth, shoots grow
away from it gravitropism roots grow toward
source of gravity toward earth will also usually
be toward water
water needed for survival patterns of roots
depend on which ones successful in encountering
water (not seeking water)
90º
34
DEVELOPMENTAL RESPONSES TO THE ENVIRONMENT
3. TOUCH tendrils twine around
supports thigmotropism - change in rate of
growth of one side vs. other - or rapid change
in turgor to fold leaves
Mimosa pudica sensitive plant
branches rubbing against each other develop more
bark!
35
DEVELOPMENTAL RESPONSES TO THE ENVIRONMENT
4. LIGHT many responses including
photosynthesis! photomorphogenesis (presence
of light) controls development (leaves,
greening) phototropism (direction) -
controls direction of growth (toward/away)
photoperiodism (quantity/duration) daylength
- controls flowering in many (vegetative ?
reproductive transition) short day plants
flower as days lt some critical length
(fall) long day plants flower as days gt some
length (late spring) day neutral something
else regulates flowering note sometimes need
more than one signal e.g., short days cold
before will flower! 5. MISCELLANEOUS -
herbivores, pathogens, symbionts, other plants,
etc.
36
DEVELOPMENTAL RESPONSES TO LIGHT
All responses to light involve 3 system
components 1. photoreceptor detects light 2.
signal transduction system secondary
messengers transmit and amplify signal 3.
response system gene activation (or
de-repression)
plants respond to light 1. presence 2. quality
(wavelength) 3. duration/quantity
(daylength) 4. direction
nucleus
37
MAJOR PHOTORECEPTORS (PIGMENTS)
photosynthetic accessory pigments
chlorophylls, carotenoids, xanthophylls anthocyani
ns color/attractiveness to pollinators or
seed/fruit dispersers photoprotection?
38
MAJOR PHOTORECEPTORS

• PHYTOCHROME (PHY) - absorbs red/far-red light
• essentially involved in determining daylength
  shading (quality)
• such phenomena as
• a. stem elongation in young seedlings
  emergence from soil
• b. seed germination (on surface of soil)
  seasonal
• c. promoting stomatal opening
• d. promoting leaf development - seasonal
• proplastid ? etioplast ? chloroplast (if light)
• etioplasts have no PS activity lack major
  thylakoid proteins
• Two Forms
• red-absorbing (660 nm) Pr usu.
  inactive form
• far-red absorbing (730 nm) Pfr usu. active
  form
• are interconvertible
• Pr Pfr
• is slow conversion of Pfr form to Pr form
  in dark
• red light (660-700 nm) is useable for
  photosynthesis, longer ?s not
• longer ?s pass through leaves so they
  represent SHADE!

red
far-red
39
MAJOR PHOTORECEPTORS
Pfr is more hydrophobic binds membranes better
is why is active? Phytochrome molecule 1,000
amino acids
phosphorylation activity
chromophore linear tetrapyrrole (A-D)
40
MAJOR PHOTORECEPTORS
Phytochrome experimental test for its
involvement red light ? is response (e.g. leaf
production) far-red light ? no response red
light ? far-red light ? ?? (no response) is
reversible - whatever plant sees last!
shaded plant on right receives higher ratio of
far-red to red ? increased stem elongation (
delay in leaf production) should eventually
reach white light (which includes red
light) Arabidopsis has 5 PHY genes with
overlapping functions different
sensitivities/wavelenths
41
MAJOR PHOTORECEPTORS
2. CRYPTOCHROME (CRY) - absorbs blue light
(350-450 nm) protein 650 amino
acids chromophore a flavin (FAD)
1st discovered in mutant Arabidopsis deficient
in blue light-stimulated leaf development
chromophore
plays a role in floral initiation circadian
rhythms (part of biological clock?)
flavin adenine dinucleotide
42
MAJOR PHOTORECEPTORS
3. PHOTOTROPIN (PHO) absorbs blue
light phototropism growth toward
light chloroplast migration in bright light
move to side walls protein - 1,000 amino
acids similar to cryptochrome flavin for
photoreceptor (FMN) but has kinase activity
also
chromophore
LOV domains in genes responding to light,
oxygen or voltage in phytochrome and
cryptochrome too!
flavin mononucleotide
43
SIGNAL TRANSDUCTION MECHANISMS
a. cGMP - formed by guanylate cyclase GTP ---gt
cGMP 2Pi destroyed by cGMP phosphodiesterase
discovered this by studying mutant tomato plants
that did not have good leaf or plastid
development, even in light - injected cells
with various potential 2o messengers
Viagra is an inhibitor of cGMP-phosphodiesterase,
so cGMP builds up relaxes smooth muscle in
corpus callosum allowing more blood inflow
(exact mechanism is not known)
44
SIGNAL TRANSDUCTION MECHANISMS
b. calmodulin - common 2o messenger in
plants binds 4 Ca2 ions and becomes
activated Ca2 - very low levels in cytoplasm
(lt10-7M), tightly regulated increase Ca2 by
influx or release from internal stores
45
SIGNAL TRANSDUCTION MECHANISMS
c. trimeric G-proteins one subunit (alpha) is a
GTPase (GTP-binding/hyrdolyzing) becomes
activated when binds GTP beta/gamma subunits
dissociate, and alpha moves to target GTP
hydrolysis releases it from binding to target
beta/gamma reassociated target goes back to
uninduced state
TARGET
(GTPase)
46
SIGNAL TRANSDUCTION MECHANISMS
anthocyanins
cGMP
PS I Cyt Bf/B6
PHY
G-protein
PS II ATP Synthetase LHC II
Ca2
Calmodulin
can be fairly complex with multiple
players! RESPONSE SYSTEM differential gene
expression
47
DEVELOPMENTAL RESPONSES TO PLANT HORMONES

• hormone chemical produced in one part of body
  that has effects on another part
• in plants, they typically coordinate
  growth/development among different tissues (
  plant growth substances)
• FEATURES
• act in small quantities/amounts (very
  potent/effective!)
• released into plant circulatory system
  mostly the phloem
• target cells/tissues have receptors for the
  hormone(s)
• binding triggers response (may be complex) in
  target cells
• so hormones act like a switch, rather than
  providing a blueprint
• THUS, VERY SIMILAR TO ANIMAL HORMONES!

48

• HOWEVER in plants
• hormones usually very simple organic molecules
• they function alone or in conjunction with
  other hormone(s)
• some are transported, others have effects where
  produced
• different tissues may respond very differently
  to same hormone

Classes of major plant hormones 1. auxins 2.
cytokinins 3. gibberellins 4. abscisic acid 5.
ethylene
49
AUXIN
first plant hormones to be discovered classic
experimental system sheath of cells that
covers grass seedlings early leaves
coleoptile - hollow, grows mostly by cell
elongation bends toward light specifically
BLUE light
PHOTOTROPISM growth toward (or away from)
light photoreceptor? now know it is
phototropin! hence its name
50
AUXIN
What part of the coleoptile is perceiving light?
Charles Francis Darwin (1880s)
The tip perceives the direction of light,
although it bends further downward
51
AUXIN
they suggested some type of signal is transported
downward from tip, stimulating bending below
definition of hormone before they were even known!
52
AUXIN
Peter Boysen-Jensen (1910s)
suggested that some type of diffusible chemical
is the signal involved
53
AUXIN
Fritz Went (1920s) extended Boysen-Jensens
experiments
diffusible chemical by itself could cause bending
if offset block in darkness called chemical AUXIN
(Gr.to increase)
54
AUXIN
Went Cholodny hypothesized that chemical moved
to shaded side - causes differential elongation
of cells there bend toward light
is an asymmetric distribution of auxin, hence
differential effect resulting in elongation of
shaded side
55
AUXIN
56
AUXIN
Winslow Briggs tested two hypotheses
auxin destruction
auxin redistribution
57
AUXIN
tryptophan
a-Naphthalene Acetic Acid (NAA) -synthetic
Indole Acetic Acid (IAA)
FUNCTION promotes cell elongation (in
coleoptile other places) important in
tropisms (photo- gravi-) and in apical
dominance phototropism bending toward sun
puts leaves in the sun, so it promotes
photosynthesis!
58
AUXIN
exists in free form or conjugated to amino
acids/sugars (inactive) - can readily be
released and have effects effective at 10-5 down
to 10-10 M! (gt10-4 M herbicidal
effects) different sensitivities in different
organs stem 10-5 M auxin stimulates
elongation root only 10-7 10-9 M auxin
necessary for response Agent Orange
defoliant/herbicide 50/50 mix of 2,4-D
2,4,5-T 2,4-dichlorophenoxyacetic acid
2,4,5-trichlorophenoxyacetic acid
also had contaminating dioxin teratogen (birth
defects) Auxin is produced in shoot
apex, leaf tips, etc. from tryptophan moves
down through plant has effects on target tissues
59
AUXIN
Acid Growth Hypothesis
auxin binds to receptor produces and activates
pumps H pumped out of cell, K brought in to
maintain turgor
H
K
K
H
auxin receptor
H
Target Cell
wall pH drops from 5.5 to 4.5 breaks bonds in
wall matrix loosens cell wall
H
K
K
H
cell wall
pH drop also activates EXPANSINS proteins in
cell walls
60
EXPANSINS ELONGATION
promote wall loosening not sure how they work!
61
AUXIN
roots grow toward Earth shoots grow away from
Earth opposite responses to the same
stimulus gravity GRAVITROPISM
90º
62
AUXIN
statocytes in root cap
statoliths amyloplasts (colorless
chloroplasts that store starch)
are heavier than cytoplasm so they sediment to
lower side of cell
root cap
63
AUXIN
auxin moves downward outward in vertical
root if shifted to horizontal, statoliths within
the statocytes sediment - believe they contact
membrane-bound receptor molecules statolith
movement triggers auxin redistribution to lower
side of root greater concentration of auxin on
lower side of root actually inhibits cell
elongation, so root bends downward
64
AUXIN
axillary buds often delay their outgrowth until
they are some distance away from the shoot apical
meristem (in many plants)
APICAL DOMINANCE
65
AUXIN
auxin from shoot apical meristem INHIBITS
outgrowth of axillary buds if pinch/cut off
apex, get bud outgrowth - used by
horticulturists to get bushy plants!
if smear cut surface with auxin - buds do NOT
flush out! cytokinins promote bud outgrowth -
ratio between hormones is what is important here!
66
AUXIN

• other auxin effects
• basipetal movement of auxin in spring causes
  vascular cambium to become active cell division
  and differentiation, especially xylem
• leaflet initiation in compound leaves
• ? gametophyte patterning egg cell identity
• cell fates in regions of plant embryos, etc.
• Auxin itself is NOT responsible for the variety
  of responses that it elicits
• - cells/tissues themselves (depending on type)
  determine their responses to auxin
• - auxin is the switch that elicits
  cell/tissue-specific responses

67
AUXIN

• Summarize
• auxin helps a cell to determine where it is
  relative to other cells
• it helps a cell to determine where it is
  relative to the shoot apex
• it is critical in determining plant morphology,
  especially if conditions change (e.g., light,
  physical orientation, damage, etc.)

68
CYTOKININS
are purines chemical variations on
adenine naturally-occuring ones
zeatin
isopentenyl adenine
(kinetin is a synthetic one)
produced mostly in root apical meristems transport
ed to shoot system axillary buds
69
CYTOKININS
functions 1. promote cell divisions in target
cells (hence name) in apical meristems
maintenance of meristems! 2. promote axillary
bud outgrowth 3. balance root/shoot growth so
vigorous root growth can support greater shoot
system 4. important in seed development -
found in endosperm (including coconut milk)
in cotyledons 5. may delay senescence in
leaves? is our lab experiment! 6. role in
stimulating differentiation activity of
vascular cambium (in conjunction with auxin)
7. activate root nodule formation (if
symbionts) appear to work in conjunction with
auxin in many cases tobacco pith tissue culture
high auxcyt stimulates development of roots
low auxcyt stimulates development of
shoots (well see what happens in our own
tissue culture experiments!)
70
GIBBERELLINS
large number of them are known so they are
given numbers! Gibberellic Acid 3 (GA3) most
common GA1, GA3 and GA4 all active forms in
plants all have gibberellane ring structure
produced mostly in uppermost leaves transported
to rest of plant
71
GIBBERELLINS
functions 1. cause cell division and stem
elongation in dwarf mutants that defective in
gene encoding enzyme involved in GA synthesis
72
GIBBERELLINS
2. growth and differentiation in vascular
cambium works with auxin cytokinin - cause
phloem differentiation 3. transition from
vegetative to reproductive state in some
plants 4. significant roles in seed
germination a. stimulate embryo to renew
development b. increase a-amylase levels (for
starch breakdown) c. activate a-amylase
73
GIBBERELLINS
how do they work? 1. promote cell wall
extensibility but different from auxin
effects some cells that unresponsive to auxin,
do respond to GA 2. modulate gene expression (in
cambium and in seeds) in unbound state, DELLA
proteins inhibit transcription by binding
transcription factor involved here when GA bound
to receptor, DELLA degraded releasing
transcription factor here acts as a
de-repressor promoting a-amylase synthesis
74
ABSCISIC ACID (ABA)
one single compound that generally is a growth
inhibitor produced in leaves moves
out into other parts but not sure what does
dry roots send ABA to shoot to prepare for
drought Functions 1. promotes dormancy in
seeds antagonist of GA here!? 2. promotes
responses associated with plant STRESS
closes stomates wilting induces mesophyll
cells to produce ABA - it acts on guard cells
to close stomates
75
ABSCISIC ACID (ABA)
ABA mutants are wilted, and seeds germinate
prematurely! misnamed! original
plant found it in ABA involved in leaf
abscission is not the case for most plants!
76
ETHYLENE
simple gas is volatile so must be continuously
produced acts locally (unlike most
hormones!) Functions 1. fruit ripening can
smell it! find at low levels early in fruit
development acts as positive feedback produce
more as ripen sudden increase climacteric
(not all fruits like this)
77
ETHYLENE
low pH chlorophyll starch pectin large organics
tastier color stands out sweeter softer sweet
smelling aromatics
kinases neutralize acidity hydrolases break down
chl. amylases starch pectinases
pectin hydrolases organics
78
ETHYLENE
2. leaf abscission does play role here, unlike
ABA decrease in auxin in shoot leads to
ethylene production in leaf abscission
zone ethylene inhibits auxin transport - so
further decreases auxin ethylene induces more
ethylene degradative enzymes once thought to
initiate apoptosis in abscission zone latest
data suggest are changes in the cell walls in
abscission zone leaf drops causes
induction of corky cells at the site of
abscission which seals wound (leaf scar) many
effects similar to those of auxin some have
postulated that auxin induces ethylene, and
ethylene is what has the effect! (other cases
they are antagonistic)
79
OTHER PLANT HORMONES

• Brassinosteroids promote cell elongation,
  reduce stress from injury, xylem development,
  etc.
• 2. Jasmonic Acid resist fungal infections and
  other stresses
• 3. Salicylic Acid perception of pathogen attack
• 4. Systemin (polypeptide) internal signaling of
  wounds
• (Ala-Val-Gln-Ser-Lys-Pro-Pro-Ser-Lys-Arg-Asp-Pro
  -Pro-Lys-Met-Gln-Thr-Asp )
• 5. Azelaic Acid accumulates in sap confers
  local systemic resistance against a
  pathogen - primes plants to accumulate
  salicylic acid!
• 6. Strigolactones inhibit shoot branching
  involved in root communication with
  mycorrhizal fungi
• these and others are not as well understood yet
  but many relate to stress responses

80
Hormone Receptors occur in various places
within the target cells
81
MEDICAL SIGNIFICANCE Paclitaxel (taxol) most
widely-used anti-cancer drug (breast ovarian
cancer) from Yew tree adding methyl
jasmonate to cell cultures - increases amount
of taxol produced! Acetylsalicylic Acid
aspirin most widely-used pain medication!