Signaling Systems Within The

Plant: A New Era of Under-

standing

Phil Thomas

Senior Agri-Coach

Agri-Trend Agrology

Factors affecting Yield and

Quality

Yield

• Soil Type

• Organic Matter

• Soil Texture

• Soil pH

• Soil Aggregate Size

• Rooting Depth

• Field Topography

• Ion & Cation Exchange

Capacity

• N, P, K, S, Ca, B, Cl, Mg, Mn,

Mo, Fe, Zn levels

• Field location /latitude

• Soil Water Holding Capacity

• Soil Aeration

• Soil Water Infiltration Rates

• Soil Crusting

• Soil Drainage

• Field Slope

• Rain & Snow

• Solar Radiation

• Evapotranspiration

• Carbon Dioxide

• Relative Humidity

• Wind Velocity

• Soil & Air Temperature

• Frost Free Days

• Oxygen

• Hail

• Flooding

• Rotation – Crop &

Pesticide

• Seedbed Firmness

• Pests – Weed, Insects &

Diseases

• Harvest/Swath Date

• Variety

• Seed Quality

• Seed Treatment

• Seeding Date, Rate, Depth

& Speed

• Pesticide – Choice &

Timing

• Tillage Intensity

• Fertilizer – Source, Rate,

Placement & Timing

Management of Factors • Due to multiple “Stress” factors

crops do not reach their genetic

yield potential

• Plants are continually exposed to

abiotic and biotic stresses that

negatively influence growth and

development

What is the most important input to

crop production?

Maximizing Photosynthetic Efficiency

2CO2 + 2H2O → C6H12O6+ 6O2

Nitrogen

Calcium

Potassium

Sulfur

Nitrogen

Phosphorus

Magnesium

Oxygen Carbon

Oxygen

Zinc

Copper

Boron

Manganese

Iron

Hydrogen

Chloride

Molybdenum

Life Cycle in Plant Cells

• Most plant life cycle

processes occur at

the plant cell level

regulated by genes.

• Every biochemical

activity in a plant is

regulated by genes!

1. Photosynthesis Sugars

Carbohydrates

(including starch)

2. Respiration (Krebs Cycle)

Makes

ATP Energy

Amino Acids

CO2

H2O

CO2 & H2O O2

+ N

Cellulose Lignins Proteins

+ S

•Nucleic Acids

- DNA, RNA

•Chlorophyll

•Growth Regulators

•Etc.

4. Transpiration

3.S

yn

thesis

Lipids

How a plant works at the molecular level

5.T

ran

s -

locati

on

Think like

a plant

Plant Genetics, Physiology and

Biochemistry

• What’s really changed in the past 10

years is:

• the shift from Genomics (number and

types of genes involved)

• to Proteomics (protein products of the

genes)

• and now Metabolomics (metabolites).

Genes Regulate

Vegetative growth:

Germination,

seedlings,

shoots, roots and

branches

Reproductive growth:

# of buds, flowers,

pods, seeds, and

seeds per pod

Yield:

Biomass, plant height, dry

matter, drought stress, heat

stress, and leaf area index

Genes Regulate

Chemical

composition:

Hormones:

Abscisic acid

Auxins

Cytokinins

Ethylene

Gibberellins

Others

For lignin content,

Oil/protein content,

Carbohydrates

And amino acids

Proline content:

(mineral elements)

Cytoplasmic streaming

Improved

enzyme

activity

Genes Regulate

Photosythesis

efficiency:

Leaf assimilation

Total chlorophyll

content and

intensity

Water use efficiency

Water management -

through lower stomata resistance

Higher intensity of transpiration

Increased water uptake by roots

Plant signaling Systems (genes)

Hormones

Peptides Or

PGR’s

Macro-proteins which are snippets of mRNA sent from cell to cell via the phloem. (transport and defence against various stresses)

Plant signaling genes

Hormones Peptides Or

PGR’s

Signals are

secreted in

response to

environmental

factors (nutrient

abundance,

drought, light,

temperature,

chemical or

physical stress)

Germination, Rooting, Growth, Flowering, Foliage, Death

Ho

rmo

ne L

evels

Key Nutrient

Hormone

Co-factors:

GA

STAGE II:

Vegetative

Growth

B, Ca, Cu, Fe, K, Mg,

Mn, Zn, amine N

Cell

Sizing

Cytokinin

STAGE I:

Germination &

Establishment

Ca, Fe, Mg, Mn, N,

P, Zn, B

Cell Initiation[ Cell Division ]

Ethylene

STAGE III:

Flowering &

Reproduction

B, Ca, Cu, K, Mg, Mo,

amine N

Cell

Maturity

ABA

STAGE IV:

Fruit Sizing &

Maturity

B, Cu, K, Mg, Mn, Mo, P

amine N

Senescence

Auxin

Seed Germination Seeds imbibe 45% of their weight in

water which leads to swelling and

seed coat breakage.

Genes activated hydrolytic

enzymes break down stored oils and

proteins into chemicals (+oxygen)

for metabolism and growth.

Oxygen is used in aerobic

respiration for energy until the plant

has leaves. Once the radicle

emerges germination ends.

Cytokinin (CK) • Root tips = factories of cytokinin

synthesis (involved in hormone

metabolism, up-take of macro-nutrients,

protein synthesis + morphological

response)

• Nitrate, sulfate and phosphate stimulates

CK production in the roots and later in

the shoots. In leaves CK involved in

stomata opening + the above root factors.

Plant Signaling Systems

• Plants are good at math!

• Receptors (internal clock) within the leaves at

night calculate amounts of starch available and

estimate time to dawn.

• Signals adjust rate of consumption so the leaves

don’t starve from lack of energy until the sun

returns.

• This helps the plants continue to grow in the

dark

Britain’s John Innes Centre – Journal of eLife

Plant Signaling Systems

• Signaling systems allow plants to see,

smell and feel (also movement).

• Plants have the ability to sense the

environment and adjust their

morphology, physiology and phenotype

accordingly.

Plant Signaling Systems

• Plants perceive and can react to stimuli

such as chemicals, gravity, light,

moisture, infections, temperature, oxygen

and carbon dioxide concentrations,

parasite infestation, physical disruption,

and touch. Plants have a variety of means

to detect such stimuli and a variety of

reaction responses.

Plant Signaling Systems (smell)

• For example a willow tree branch being

attacked by tent caterpillars produces

salicylic acid (SA) which makes its leaves

taste bitter and unpalatable. This signal

of SA is also released into the air and

detected (smelled) by nearby branches or

trees which then also produce SA

providing protection.

• Lima beans attacked by an insect or

bacteria do it too.

Plant Signaling Systems (smell)

• Wounded tomatoes are known to

produce the volatile odour methyl-

jasmonate as an alarm-signal when

attacked. Plants in the neighbourhood

can then detect the chemical and prepare

for the attack by producing this or other

chemicals that defend against insects or

attract predators.[5]

Plant Signaling Systems (feel)

• The effect of

touching a Mimosa

plant with fingers

causing the leaves

to rapidly fold up.

• The cocklebur weed

can die simply by

touching it a few

seconds for a few

days

Photo Receptors

• These light sensors detect shading from

neighbours and produce a signal “auxin”

which causes some plants to grow taller.

• There are likely over 300 kinase proteins

in canola with many diverse functions

and pathways. These signals are involved

in developmental and defence functions.

(P-NB)

Plant Signaling Systems

(movement)

• For example

sunflowers with

photo receptors

send signals to

slowly move heads

with the sun.

• Another is the

Venus fly trap.

Canola Life Cycle

Plant Signaling Systems • Plants can see UV

light (red & blue)

via photo receptor

proteins.

• Canola plants need

over 10 to 12 hours

of day length/day

before the

reproductive stage

processes start.

GDD’s (0 base)

Reproduction – B is essential

Hours after plant receptors find required DL + GDD’s

FT gene in all leaves makes a

signal molecule called FT

protein.

Transported by phloem to growing tip

combines with and

activates a FD

protein from an FD

gene.

FT/FD signal

Acts on genes - turns stem cells into flower buds

Canola Sex - Flowering

Immature Bud

Immature Stigma

Immature anthers

Canola Sex - Flowering

Flower opens

within 2-3 days pollen

is produced by

anthers

Canola Sex - Flowering

Anthers mature and release pollen

Stigma tip has adhesive to capture

pollen

Canola Sex - Flowering

Pollen land on the

stigma and absorbs

water and nutrients

from the stigma to

germinate and form a

pollen tube

Over 100 pollen grains are required on the stigma to

fertilize all the ovules

GABA Key signalling molecule that triggers pollination – Boron is a precursor

Stigma

Ovules

1st ovule that matures sends out the GABA signal

once 1st ovule is pollinated

the next ovary starts to

send the signal etc

Pollen tube follows the signal and pollenates the 1st ovule

Pollen grain

Takes only a couple of days or less for each flower for complete pollination

Pollen Tube

If boron is deficient the tip of the pollen

tubes will burst and no pollination will occur

Flowering

• From the start to the end of flowering

there are about 8 to 9 Gibberellins

involved that have effects on seed

formation, proteins and oil.

• Gibberellins are also critical for root

growth as they regulate numbers of cells

and their size.

• K and Zn essential

Plants on Steroids • Brassinosteroids from chloroplasts, join a

protein on the surface of a plant cell and

send signals to the cell's nucleus causing

plant genes to be expressed. (P is

important as the signal is a protein

phosphatase).

• Chemical signals activate a cascade of

gene activity regulating growth and

development (response to gravity, light,

& resist stresses).

Plant Signaling Systems • Water movement is controlled by a cell

membrane gene that produces an

aquaporin (macro-protein) signal. This

signal opens or closes cell membrane

water/protein channels when drought or

waterlogging occurs resulting in

improved water use efficiency and

movement.

• There are about 35 aquaporin’s in plants.

• Phosphorus is important

Water Management

• Understanding how roots grow and how

hormones control that growth is crucial

to improving crop yields.

• A gibberellin protein signal plays a

crucial role in controlling the size of the

root meristem, and that it is the

endodermis which sets the pace for

expansion rates in the other root tissues.

Water Management

• Carbon is essential

for all life!

• CO2 critical for

photosynthesis.

• Plants open stomata

during the day – a

problem - take in

CO2 but lose water

vapour.

Water Management

• When roots sense a

water shortage they

send a macro-

protein signal to

produce absicsic

acid (ABA) that’s

translocated to the

leaves which closes

the stomata.

• K & Ca are NB

Water Management • ABA triggers a signalling cascade in

stomatal guard cells which closes the

stomata reducing water loss.

• ABA induces the production of H2O2 in

guard cells which then activate calcium

channels – Both ABA and H2O2 induced

Ca channels are important mechanisms

for stomata closing.

• Therefore K and Ca are important

Signals Involved with Nutrients

• It is important to understand the

molecular basis of nutrient uptake and

transport within the plant and the genes

responsible

• Uptake and transport of nutrients are

gene regulated by signals

Signals Involved with Nutrients

• For example there are 14 genes (that we

know of) involved in the transporters

(uptake and transport) of sulphur within

the plant

• These genes are in 5 groups (in the roots,

leaves, stems and cell to cell)

• There are many more genes regulating

transporters of Mg (7) N (37) and P (142)

Signals Involved with Nutrients

• Where S is deficient = big yield loss

• But if S is added then uptake of Se and

Mo is decreased due to the sulfate

transporter expression and competition

from Mg, N & P transporter genes.

• But if Mg, N & P up-regulated genes are

switched on S uptake is increased

Nutrients Involved with Signals

• Nutrients are critical for the production

of signals and/or for the products

produced (metabolites, enzymes, etc.)

• For example biological nutrients are key

for making enzymes:

• Ni (2) Mo (4) Mn (50)

• Fe (100) Cu (100) Zn (1200)

Nutrients Involved with Signals • While Mo is only involved with 4

enzymes it is critical for plant growth

– Nitrate reductase – no N nutrition without

Mo

– Sulfite oxidase – NB in chloroplasts

– Zanthize dehydrogenase – disease defense

– Aldehyde oxidase – NB in hormone signals

metabolism (cytokinins, ABA, Auxins, ROS

• Mo is a cofactor for Moco sulfurase (MG,

S & Fe) a protein for drought tolerance.

Nutrients Involved with Signals

• There are a large # of genes that regulate

molecular processes that respond to K.

• Jasmonic acid – a defence metabolite

• K is involved in signals for accumulation

of secondary Jasmonic defense

metabolites for fungal, bacterial, viral

and insects attacks. Therefore, plants are

healthier.

Nutrients Involved with Signals

• Cu, Zn & Mn are co-factors for a large

number of enzymes such as SA which

results in “systemic acquired resistance”

improving disease resistance.

• There is a synergism with seed

treatments and seed quality, health and

yield.

Protection Response

• Plant with no stress (weather, nutrients,

disease, water, good rooting depth, etc)

may only have 3 genes (turned on or off)

so there is limited resistance activity.

• But in plants with stress there may be 60

to 70 genes which are strongly affected

under stress (and turned on).

Protection Response

• SAR – “systemic acquired resistance”

that is dependant on phytohormone

salicylic acid.

• An attacking pathogen secretes effectors

(Avr) that are recognized by plant

resistance proteins (R) which trigger the

development of hypersensitive response

(HR) which activates a SAR signal.

Protection Response • The SAR signal leads to production of

protection proteins (PR) throughout the

plant which act against a broad spectrum

of the same or other pathogens.

• One of these is the “Shikimic acid

pathway” (phyto alexins) which takes

away nutrients from around the disease

infected areas starving the disease. P is

important.

Shikimic Acid Pathway

Protection Response

• Attacks by predators/diseases trigger

signals that provide defense. In canola

there is a glucosinolate/myrosinase

system triggered that produces more

glucosinolates and trichomes which are

stored in the cell vacuoles to protect the

plant.

Protection Response

• The high levels of glucosinolates may

deter some insects/diseases BUT may also

attract specialist bugs through phenols

that are given off by the plant.

• Sulphur is essential for production of

glucosinolates.

Conclusion

• Understanding precisely how plant

signaling systems and hormones regulate

plant growth is one of the key areas of

fundamental plant biology which will

underpin crop improvements in the

future!

Thank You