Plant Physiology Plant Physiology ChaptersChapters

Angiosperms – Flowering PlantsAngiosperms – Flowering Plants

AP BiologyAP Biology

Chapter 1Chapter 1Plant Form and Plant Form and

FunctionFunction

Monocots vs. DicotsMonocots vs. Dicots

Grass, wheat, corn , Grass, wheat, corn , rice, sugar canerice, sugar cane

Fibrous rootsFibrous roots Parallel veinsParallel veins Flowers in 3’sFlowers in 3’s

Most othersMost others

Tap RootsTap Roots Net-like veinsNet-like veins Flowers in 4’s and 5’sFlowers in 4’s and 5’s Can become woody Can become woody

Plant Organs and TissuesPlant Organs and Tissues

Organs:Organs: roots, stem, leaves – all organs are made out of the roots, stem, leaves – all organs are made out of the same three tissuessame three tissues

TissuesTissues Dermal Tissue – epidermis – protectiveDermal Tissue – epidermis – protective Vascular Tissue – veins – carry food and waterVascular Tissue – veins – carry food and water

Xylem – carries water and minerals – made of tracheids and vessel Xylem – carries water and minerals – made of tracheids and vessel elementselements

Phloem – carries sugar – made of sieve tubes and companion cellsPhloem – carries sugar – made of sieve tubes and companion cells Ground Tissue – everything else – used for support, Ground Tissue – everything else – used for support,

photosynthesis, storagephotosynthesis, storage Pith-ground tissue inside vascular tissuePith-ground tissue inside vascular tissue Cortex-ground tissue outside of vascular tissueCortex-ground tissue outside of vascular tissue

Outside layer = epidermis – dermal tissue for protection

Cortex = ground tissue – storage of food, uptake of minerals

Steele = xylem and phloem – vascular tissue

Root Hairs – increase surface area for increased water absorption

Root vs. Shoot SystemRoot vs. Shoot System Root system (roots)Root system (roots)

Takes water and minerals Takes water and minerals from the soil from the soil (absorbs from the tips of the roots and root hairs increase surface area from absorption)

Anatomy:Anatomy: Tap roots (dicots) – a large Tap roots (dicots) – a large

vertical root with smaller lateral vertical root with smaller lateral roots (store food)roots (store food)

Fibrous roots (monocots) – Fibrous roots (monocots) – mat-like roots that spreadmat-like roots that spread

Shoot system (stem, leaves, Shoot system (stem, leaves, flowers)flowers)

Takes CO2 from the air, make Takes CO2 from the air, make sugar, plant reproductionsugar, plant reproduction

Transports sugar to the rest of Transports sugar to the rest of the plantthe plant

AnatomyAnatomy Stems:Stems:

Nodes – where leaves attachNodes – where leaves attach Buds – create more shootsBuds – create more shoots

Terminal buds – end of stem – Terminal buds – end of stem – cause apical dominance – cause apical dominance – inhibits side growthinhibits side growth

Axillary buds – side budSAxillary buds – side budS

Leaves: Petiole – attaches leaf to Leaves: Petiole – attaches leaf to the node (not in monocots – leaf the node (not in monocots – leaf ensheathed in stem)ensheathed in stem)

Flowers – modified leaves with Flowers – modified leaves with stem specialized for reproductionstem specialized for reproduction

Roots:

Epidermis – dermal

Cortex – ground

Vascular - vascular

Dicot Root

Stems

Cortex

Epidermis

Vascular Bundle

Vascular Bundle

Monocot – C4 Plant→

←Dicot – C3 Plant

Plant Cell TypesPlant Cell Types ParenchymaParenchyma – “normal plant cells” – have large vacuoles, no – “normal plant cells” – have large vacuoles, no

secondary cell wall, usually not mitotic, but can be stimulated secondary cell wall, usually not mitotic, but can be stimulated to divide in injuryto divide in injury

Examples: Most of the cells that make up ground tissueExamples: Most of the cells that make up ground tissue Photosynthetic cells in leaf mesophyllPhotosynthetic cells in leaf mesophyll Cells that store starch in stems and rootsCells that store starch in stems and roots Fruit cells – store sugarFruit cells – store sugar Sieve tube cells that make up phloemSieve tube cells that make up phloem

CollenchymaCollenchyma – cells are elongated, thicker primary wall but – cells are elongated, thicker primary wall but no secondary cell wall, provides for growth and supportno secondary cell wall, provides for growth and support

Examples:Examples: Cells that support young stems and petiolesCells that support young stems and petioles Some ground tissueSome ground tissue

SclerenchymaSclerenchyma – rigid secondary cells walls (can’t elongate), – rigid secondary cells walls (can’t elongate), may be dead and used for plant supportmay be dead and used for plant support

Examples:Examples: The shells of nuts and outer coat of seedsThe shells of nuts and outer coat of seeds Fiber cells – used to make plant fibers that are used to make ropeFiber cells – used to make plant fibers that are used to make rope Tracheids and Vessel Elements (make up xylem) – dead water conducting cells Tracheids and Vessel Elements (make up xylem) – dead water conducting cells

used for support (cells disintegrate leaving empty cell with a double cell wall – used for support (cells disintegrate leaving empty cell with a double cell wall – water moves from cells to cell through pits or end to end perforationswater moves from cells to cell through pits or end to end perforations

sclerenchyma

Plant GrowthPlant Growth

Meristems embryonic tissue (stem cells – Meristems embryonic tissue (stem cells – undifferentiated) – can divide and become any undifferentiated) – can divide and become any kind of plant cellkind of plant cell

Primary Meristems(apical) – make plant grow Primary Meristems(apical) – make plant grow longer – in root tips and at buds or new shootslonger – in root tips and at buds or new shoots

Secondary Meristems(lateral) – make plant Secondary Meristems(lateral) – make plant grow wider – in stem – adding more xylem grow wider – in stem – adding more xylem which becomes woodwhich becomes wood

Lateral GrowthLateral Growth Lateral Meristems also called vascular cambium – Lateral Meristems also called vascular cambium –

forms between xylem and phloem so there is a forms between xylem and phloem so there is a continuous cylinder around xylem and interior continuous cylinder around xylem and interior ground tissueground tissue

It forms 2ndary xylem on the inside and 2ndary It forms 2ndary xylem on the inside and 2ndary phloem on the outsidephloem on the outside

Lateral GrowthLateral Growth

Xylem (wood) Over the years, vascular cambium Xylem (wood) Over the years, vascular cambium makes many layers of 2ndary xylem on the inside makes many layers of 2ndary xylem on the inside (made of tracheids and vessel elements with very (made of tracheids and vessel elements with very strong cell walls) – This is wood! Only the most strong cell walls) – This is wood! Only the most exterior xylem works to carry water. Interior xylem exterior xylem works to carry water. Interior xylem dies and harden moredies and harden more

Phloem (part of bark) Formed outside the vascular Phloem (part of bark) Formed outside the vascular cambium – only newest xylem closest to interior is cambium – only newest xylem closest to interior is alive and transports food – rest dies and sloughs off alive and transports food – rest dies and sloughs off so doesn’t become thick like wood partso doesn’t become thick like wood part

Lateral Growth continuedLateral Growth continued

Cork cambium forms outside the phloem and Cork cambium forms outside the phloem and makes cork cells which fill with suberin – a makes cork cells which fill with suberin – a waxy material that protect the trunk and waxy material that protect the trunk and branchesbranches

The epidermis cracks off and the outside The epidermis cracks off and the outside becomes the cork cellsbecomes the cork cells

Bark = Phloem, Cork Cambium, CorkBark = Phloem, Cork Cambium, Cork

Heartwood = dead, older xylem

Sapwood = new xylem still carrying water

Phloem – carries food - old phloem sloughs

Plant TransportPlant Transport22ndnd Plant Chapter Plant Chapter

Chapter 36Chapter 36

I. Local Transport (all review)I. Local Transport (all review)A.A. Facilitated DiffusionFacilitated Diffusion

a.a. Open channelsOpen channelsb.b. Shape change channels (not regulared by ATP must by solutes Shape change channels (not regulared by ATP must by solutes

moving thru)moving thru)c.c. Gated channelsGated channels

B.B. Active TransportActive Transporta.a. NormalNormalb.b. Chemiosmosis – coupling the pumping of protons to the movement Chemiosmosis – coupling the pumping of protons to the movement

of other solutes (ex. Pump protons to cause the movement of K+ into of other solutes (ex. Pump protons to cause the movement of K+ into guard cells)guard cells)

c.c. Co-transport – pumping protons, they attach to solutes and move Co-transport – pumping protons, they attach to solutes and move them passively as they flow back thru the membranethem passively as they flow back thru the membrane

Examples:Examples:1. bringing nitrogen into the roots (pump H+ out of the epidermis into 1. bringing nitrogen into the roots (pump H+ out of the epidermis into the soil and as it flows back it in brings nitrogenthe soil and as it flows back it in brings nitrogen2. loading sucrose into the phloem (pump H+ out of sieve tubes in 2. loading sucrose into the phloem (pump H+ out of sieve tubes in phloem into the leaf mesophyll and it flows back bring sucrose with it)phloem into the leaf mesophyll and it flows back bring sucrose with it)

C.C. Osmosis – remember in plants, water doesn’t just move Osmosis – remember in plants, water doesn’t just move from high to low concentration, pressure also plays a role from high to low concentration, pressure also plays a role and can override solute and water concentrationand can override solute and water concentration

Osmosis ContinuedOsmosis ContinuedΨΨ = = ΨΨpp + + ΨΨss

Water potential – the tendency for water to leave one Water potential – the tendency for water to leave one place and go to another – the higher the place and go to another – the higher the ΨΨ the more the more likely water will leave and go somewhere elselikely water will leave and go somewhere else

Water moves from high to low water potentialWater moves from high to low water potential

Water potential = pressure potential + solute potentialWater potential = pressure potential + solute potential

Pressure potential is usually positive created by the Pressure potential is usually positive created by the pressure exerted by the cell wall – the higher the pressure exerted by the cell wall – the higher the pressure potential – the higher water potentialpressure potential – the higher water potential

Solute potential is 0 in pure water and negative if there Solute potential is 0 in pure water and negative if there are any solutes - the more solutes the more negative are any solutes - the more solutes the more negative solute potential and the lower the water potential – water solute potential and the lower the water potential – water moves where there is more solute!moves where there is more solute!

II. Lateral Movement – short II. Lateral Movement – short distancedistance

There are three compartments within plant cells:There are three compartments within plant cells: Apoplast – continuum of cell wallsApoplast – continuum of cell walls Symplast – continuum of cytoplasm thru Symplast – continuum of cytoplasm thru

plasmodesmataplasmodesmata Tonoplast – vacuole compartment set apart by the Tonoplast – vacuole compartment set apart by the

vacuole membrane – not continuous from cell to cell vacuole membrane – not continuous from cell to cell and the vacuole membrane can actively transport and and the vacuole membrane can actively transport and do chemiosmosisdo chemiosmosis

Water and solutes can move through the apoplast, Water and solutes can move through the apoplast, symplast, or into the tonoplastsymplast, or into the tonoplast

Lateral Movement in PlantsLateral Movement in Plants

III. Long Distance Transport III. Long Distance Transport (vertical movement thru xylem and (vertical movement thru xylem and

phloem – diffusion is too slowphloem – diffusion is too slowA. Xylem (tracheids and vessel elements with 2 A. Xylem (tracheids and vessel elements with 2

set of cells walls) - schlerenchymaset of cells walls) - schlerenchyma

Tracheids↑↑

↑↑

Vessel Element

Xylem ContinuedXylem Continued

Water and mineral transported from roots to leavesWater and mineral transported from roots to leaves To get into the xylem – things pass from the To get into the xylem – things pass from the

epidermis of the roots into the cortex and into the epidermis of the roots into the cortex and into the steele which then branches into the xylem in the stemsteele which then branches into the xylem in the stem

In roots, root hairs increase surface area to absorb In roots, root hairs increase surface area to absorb more thru the epidermismore thru the epidermis

Endodermis (between cortex and steele) is selective Endodermis (between cortex and steele) is selective in what mineral can cross into the steelein what mineral can cross into the steele

Xylem continuedXylem continued

Xylem has two methods of movement:Xylem has two methods of movement: Main method is transpiration accompanied by Main method is transpiration accompanied by

cohesion and adhesion (transpiration caused by cohesion and adhesion (transpiration caused by lower water potential in air than in mesophyll of lower water potential in air than in mesophyll of leaf)leaf)

Second method that helps some is root pressure. Second method that helps some is root pressure. Minerals are actively transported into the xylem in Minerals are actively transported into the xylem in the root which decreases water potential in the the root which decreases water potential in the xylem cells, water flows in and pushes the water xylem cells, water flows in and pushes the water up (only good for a few meters)up (only good for a few meters)

Movement of Water - TranspirationMovement of Water - Transpiration

Xylem continuedXylem continued Regulation of Transpiration controls the flow of Regulation of Transpiration controls the flow of

water thru the plant and also makes sure that the plant water thru the plant and also makes sure that the plant doesn’t dry out and have no water for photosynthesisdoesn’t dry out and have no water for photosynthesis Guard cells buckle outward when full of waterGuard cells buckle outward when full of water Guard cells flap closed when empty (when water is Guard cells flap closed when empty (when water is

lacking, turgor pressure decreases and the cells become lacking, turgor pressure decreases and the cells become flaccid and flop togetherflaccid and flop together

Also, guard cells use chemiosmosis to open and closeAlso, guard cells use chemiosmosis to open and close They pump H+ out which causes a neg. charge inside that caused They pump H+ out which causes a neg. charge inside that caused

K+ to be drawn into the cell K+ to be drawn into the cell Due to the K+ in the cell – it become hypertonic and water flows inDue to the K+ in the cell – it become hypertonic and water flows in The active pumping is stimulated by light and low CO2The active pumping is stimulated by light and low CO2 For closing, K+ is transported out in response to high temp or high For closing, K+ is transported out in response to high temp or high

CO2 (mediated by abscisic acid- a hormone)CO2 (mediated by abscisic acid- a hormone)

Long Distance Transport ContinuedLong Distance Transport Continued

B.B. Phloem (sieve tubes and companion cells)Phloem (sieve tubes and companion cells)• Sugar is transported from the leaves to storage areas of Sugar is transported from the leaves to storage areas of

the plant (roots and fruit)the plant (roots and fruit)• Phloem sap is mostly sugar in water but also contains aa, Phloem sap is mostly sugar in water but also contains aa,

hormones, and some mineralshormones, and some minerals• Sugar will diffuse thru plasmodesmata from mesophyll Sugar will diffuse thru plasmodesmata from mesophyll

cells to sieve tubes due to concentration differencecells to sieve tubes due to concentration difference• Sugar is also actively transported into the sieve tubes Sugar is also actively transported into the sieve tubes

making the sieve tube cells hypertonic so water rushes in making the sieve tube cells hypertonic so water rushes in and pushes the sugar water thru the phloem to needy and pushes the sugar water thru the phloem to needy areasareas

• Once in the phloem it moves from source to sink:Once in the phloem it moves from source to sink:• At the sink end (no sugar), sugar is leaving the sieve tubes to go At the sink end (no sugar), sugar is leaving the sieve tubes to go

into storage cells by concentration differencesinto storage cells by concentration differences• This causes pressure to decrease and sugar flows high to low This causes pressure to decrease and sugar flows high to low

pressure and high to low concentrationpressure and high to low concentration

Plant NutritionPlant Nutrition33rdrd Plant Chapter Plant Chapter

Chapter 37Chapter 37

Plant Growth – where does the Plant Growth – where does the plant’s mass come fromplant’s mass come from

1. Most of the plant weight is water1. Most of the plant weight is water Water accumulates in vacuoles and elongates the Water accumulates in vacuoles and elongates the

cells and makes them turgid and acts as a solventcells and makes them turgid and acts as a solvent

Water also supplies hygrogen which is Water also supplies hygrogen which is incorporated into sugar in the Calvin Cycleincorporated into sugar in the Calvin Cycle

90% of a plant’s water is lost in transpiration and 90% of a plant’s water is lost in transpiration and then replacedthen replaced

Plant Growth ContinuedPlant Growth Continued

2.2. Of the dry weight – 95% is organicOf the dry weight – 95% is organic Most weight is CO2 from the air that is Most weight is CO2 from the air that is

incorporated into carbohydrates (remember most incorporated into carbohydrates (remember most of structure is cell walls, made of cellulose which of structure is cell walls, made of cellulose which are strings of glucose)are strings of glucose)

3.3. Of the dry weight – 5% is inorganicOf the dry weight – 5% is inorganic From minerals from the soilFrom minerals from the soil

Macronutrients (needed in lg. amts.)Macronutrients (needed in lg. amts.)Source of macronutrients:Source of macronutrients: C, O C, O → air→ air H → waterH → water N,S,P,K, Ca, Mg → soilN,S,P,K, Ca, Mg → soil

Purpose of macronutrients:Purpose of macronutrients: C, O, H – sugar and cell wall productionC, O, H – sugar and cell wall production N, S – make proteinsN, S – make proteins N, P, - nucleic acids, ATP, phosphorylation cascades in cell signallingN, P, - nucleic acids, ATP, phosphorylation cascades in cell signalling K – water balance, opening and closing stomates, cofactor for protein K – water balance, opening and closing stomates, cofactor for protein

synthesis enyzmessynthesis enyzmes Ca – membrane structure, formation of cell walls, cofactorCa – membrane structure, formation of cell walls, cofactor Mg – part of chlorophyllMg – part of chlorophyll

Micronutrients (needed is small amts.)Micronutrients (needed is small amts.)Fe, Cl, Cu, Mn, , B, Ni → all from soil, all used as cofactorsFe, Cl, Cu, Mn, , B, Ni → all from soil, all used as cofactors

SoilSoil Soil is eroded rock and humus (dead organic stuff) and spaces Soil is eroded rock and humus (dead organic stuff) and spaces

for waterfor water Texture of soil determines the quality for certain plantsTexture of soil determines the quality for certain plants Type of soil depends on how tightly packed - sand (loosest) Type of soil depends on how tightly packed - sand (loosest) → →

clay (tightest packed)clay (tightest packed) A mix of soil types is the bestA mix of soil types is the best Soil pH affects the availability of mineralsSoil pH affects the availability of minerals Soil often gets acidic from acid rain – put own lime which Soil often gets acidic from acid rain – put own lime which

is basic – positve ions bind up negative ions and plants is basic – positve ions bind up negative ions and plants can’t get them from the soilcan’t get them from the soil

Soils with a lot of clay bind up all the positive ions like K+, Soils with a lot of clay bind up all the positive ions like K+, Ca++, Mg++, NH4+ and it’s hard for plants to get. Ca++, Mg++, NH4+ and it’s hard for plants to get. Negative minerals NO3-, PO4- don’t stay in the soil very Negative minerals NO3-, PO4- don’t stay in the soil very long and wash awaylong and wash away

Some plants secrete H+ into soil which will compete for Some plants secrete H+ into soil which will compete for binding the to clay and release the postive mi neralsbinding the to clay and release the postive mi nerals

Plants getting NitrogenPlants getting Nitrogen Needed for aa and nucleic acidsNeeded for aa and nucleic acids 80% of the air is nitrogen but N N, no enzymes 80% of the air is nitrogen but N N, no enzymes

in plants to break Nin plants to break N2 2 bond so it’s unuseable bond so it’s unuseable Plants get nitrogen from:Plants get nitrogen from:

Decomposition of organic material to inorganic Decomposition of organic material to inorganic compounds that plants can absorb (NHcompounds that plants can absorb (NH44

++, NO, NO33--, ,

ammonium and nitrate)ammonium and nitrate) Nitrogen fixation – specialized bacteria (Rhizobium) Nitrogen fixation – specialized bacteria (Rhizobium)

which live free in soil or symbiotically on plant roots which live free in soil or symbiotically on plant roots (legumes like peas, beans, soy, nuts) are able to (legumes like peas, beans, soy, nuts) are able to convert Nconvert N2 2 into useable ammonium and nitrateinto useable ammonium and nitrate

Note: Some roots have leghemoglobin to bind ONote: Some roots have leghemoglobin to bind O22 for for the bacteria to use because nitrogen fixation requires the bacteria to use because nitrogen fixation requires a lot of energy and the bacteria need a lot of oxygen a lot of energy and the bacteria need a lot of oxygen for CR for CR

Getting NitrogenGetting Nitrogen

Organic Material NH4+, NO3-NH4+, NO3- Decomposed to

Absorbed by plant roots

Denitrified by bacteria to N2 – goes back into air - unusable

OR

N2 in air

Fixed to

Getting PhosphorusGetting PhosphorusMycorrhizae – fungus living symbiotically on many plant roots, Mycorrhizae – fungus living symbiotically on many plant roots, absorb PO4- and water and secrete plant root growth factors (in absorb PO4- and water and secrete plant root growth factors (in turn the plant feeds the non-photosynthetic fungusturn the plant feeds the non-photosynthetic fungus

Note – many times in farming – there is no decomposition so farmers add fertilizer – feces containing usable nitrogen cmpds.

Plant Adaptations to get minerals Plant Adaptations to get minerals and waterand water

Parasitic plants - do some photosythesis to make Parasitic plants - do some photosythesis to make sugar but tap into other plants vascular system and sugar but tap into other plants vascular system and suck out water and mineralssuck out water and minerals

Epiphytes – grow on other plants but are fully Epiphytes – grow on other plants but are fully photosynthetic and not parastiticphotosynthetic and not parastitic

Carnivorous Plants – live in poor soil conditions – Carnivorous Plants – live in poor soil conditions – usually nitrogen deficient – capture animals for usually nitrogen deficient – capture animals for nitrogen and other minerals but are fully nitrogen and other minerals but are fully photosythetic for sugar (venus fly trap)photosythetic for sugar (venus fly trap)

Farming Practices and PlantsFarming Practices and PlantsCrops are not NaturalCrops are not Natural

1.1. Crops remove minerals from soil but don’t Crops remove minerals from soil but don’t decompose and return the organic or inorganic decompose and return the organic or inorganic components to the soilcomponents to the soil

a.a. Must use fertilizers to replace N, P, K which then can run Must use fertilizers to replace N, P, K which then can run off and cause too much plant growth in rivers – clogging off and cause too much plant growth in rivers – clogging them and killing fishthem and killing fish

• Can use natural fertilizers which are slow release vs. commercial Can use natural fertilizers which are slow release vs. commercial fertilizers which release faster but usually don’t stay in soil as fertilizers which release faster but usually don’t stay in soil as longlong

b.b. Can rotate crops – rotate with legumes – add nitrogen to Can rotate crops – rotate with legumes – add nitrogen to soil and plow them under as fertilizersoil and plow them under as fertilizer

Farming ContinuedFarming Continued2.2. Crops remove water from the soilCrops remove water from the soil

Ground aquifers collapseGround aquifers collapse Many farmers irrigate with water containing salts – as the Many farmers irrigate with water containing salts – as the

water evaporates, the soil becomes salty making the soil water evaporates, the soil becomes salty making the soil hypertonic (lower water potential) so water leaves the hypertonic (lower water potential) so water leaves the roots instead of enteringroots instead of entering

3.3. Crop harvesting causes the loss of top soil – soil Crop harvesting causes the loss of top soil – soil blows or washes away once crops are harvested. blows or washes away once crops are harvested. Can combat problem by:Can combat problem by:

Contour farmingContour farming Not plowing at the end of the seasonNot plowing at the end of the season Now planting in rows or plant plants that don’t grow in Now planting in rows or plant plants that don’t grow in

rowsrows Planting crops that trap soil – rotating cropsPlanting crops that trap soil – rotating crops

Plant Signaling and Plant Plant Signaling and Plant HormonesHormones

AP BiologyAP Biology

Plant Class #4Plant Class #4

Hormone ActionHormone ActionThe same hormone can have different effects depending on location, The same hormone can have different effects depending on location,

concentration, developmental stage or plant, etc.concentration, developmental stage or plant, etc.

Effect Gene ExpressionEffect Gene Expression Effect Enzyme ActivityEffect Enzyme Activity Change Membrane PropertiesChange Membrane Properties Open Gated ChannelsOpen Gated Channels Change MetabolismChange Metabolism Stimulate Cell DivisionStimulate Cell Division Affect the differentiation and development of Affect the differentiation and development of

cellscells

General Action of HormonesGeneral Action of Hormones

1.1. Bind to receptorsBind to receptors2.2. Receptors change shape in response to bindingReceptors change shape in response to binding3.3. 22ndnd messengers are activated which activate messengers are activated which activate

enzymes enzymes OROR4.4. Directly activate or cause transcription of enzymes Directly activate or cause transcription of enzymes

(particulary kinases which phosphorylate other (particulary kinases which phosphorylate other enzymes)enzymes)

5.5. Enzymes ultimately:Enzymes ultimately:1.1. Activate gene transcriptionActivate gene transcription2.2. Activate transcription factorsActivate transcription factors3.3. Deactivate transcriptional repressorsDeactivate transcriptional repressors4.4. Cause chemical reactionsCause chemical reactions

Example of Plant Cell SignalingExample of Plant Cell SignalingResponse to a stem breaking through the ground Response to a stem breaking through the ground

for the first timefor the first time

Light activates Phytochromes (light receptor Light activates Phytochromes (light receptor connected to a kinase)connected to a kinase)

cGMP activated

Enzymes are phosphorylated

Turn on transcription factors

Opens gated channels for Ca++ in cell membrane

Calcium binds to Calmodulin

Activated kinases and turns on transcription factors

Make Photosynthesis enzymes

Make enzymes to make chlorophyll

Make enzymes to decrease auxin production so don’t keep elongating the stems

Plant Hormones (internal signaling) Plant Hormones (internal signaling) AuxinAuxin

Produced by apical meristems, young leaves, developing seeds Produced by apical meristems, young leaves, developing seeds and fruit – generally moves from shoot to the baseand fruit – generally moves from shoot to the base

Moves through the parenchyma cells themselves – not Moves through the parenchyma cells themselves – not vascular tissue - Transported by chemiosmosisvascular tissue - Transported by chemiosmosis

In low conc. – causes cells to elongate fasterIn low conc. – causes cells to elongate faster Stimulates pumps to pump H+ into cell wall, Stimulates pumps to pump H+ into cell wall, ↓pH activates enzymes ↓pH activates enzymes

that break down cell wall – allows water flowing in to expand wallthat break down cell wall – allows water flowing in to expand wall Phototropism – growing toward light – elongates cells on dark Phototropism – growing toward light – elongates cells on dark

side fasterside faster In high concentrations - induces ethylene gas which slows cell In high concentrations - induces ethylene gas which slows cell

growthgrowth Control apical dominanceControl apical dominance Controls stem elongation in developing shootsControls stem elongation in developing shoots Kills dicots/not monocots = pesticide for corn or grass fieldsKills dicots/not monocots = pesticide for corn or grass fields Causes fruit to grow – if spray on plants, fruit will develop Causes fruit to grow – if spray on plants, fruit will develop

without seeds = seedless fruitwithout seeds = seedless fruit

CytokininsCytokinins Produced by the roots, Moves through the xylem, Produced by the roots, Moves through the xylem,

modified adenine, named for cytokinesis since in modified adenine, named for cytokinesis since in actively growing parts of plantactively growing parts of plant

Stimulates cell division in roots, embryos, fruits, Stimulates cell division in roots, embryos, fruits, retards protein breakdown and prevents aging in retards protein breakdown and prevents aging in leaves and fruits (florists spray on cut flowers to keep leaves and fruits (florists spray on cut flowers to keep them fresh), stimulates seed germinationthem fresh), stimulates seed germination

Works with auxin, relative concentrations control Works with auxin, relative concentrations control growth and differentiation of plant partsgrowth and differentiation of plant parts

Works opposite auxin to control height vs. bushiness Works opposite auxin to control height vs. bushiness (more auxin – grow tall, more cytokinins – more (more auxin – grow tall, more cytokinins – more axillary buds – bushier)axillary buds – bushier)

GibberellinsGibberellins

Produced in roots and young leavesProduced in roots and young leaves Elongation and cell division in stems and leaves Elongation and cell division in stems and leaves

(activates enzymes that allow cellulose digesting (activates enzymes that allow cellulose digesting enzymes to penetrate the cell wall)enzymes to penetrate the cell wall)

Cause germination of seeds – water stimulates release Cause germination of seeds – water stimulates release of gibberellins – stimulates production of amylase to of gibberellins – stimulates production of amylase to break down carbsbreak down carbs

Important for pollen development, pollen tube growthImportant for pollen development, pollen tube growth Works with auxin for fruit growth (spray to make Works with auxin for fruit growth (spray to make

seedless grapes)seedless grapes)

Abscisic AcidAbscisic Acid

Readies the plant for winter – slow growth of Readies the plant for winter – slow growth of buds, inhibits growthbuds, inhibits growth

Causes stomates to close in a wilting plant, Causes stomates to close in a wilting plant, opens the K+ channels so K+ leaves guard opens the K+ channels so K+ leaves guard cells, water followscells, water follows

Keep seeds dormant when conditions not Keep seeds dormant when conditions not suitable (light, rain, etc. inactivates abscisic suitable (light, rain, etc. inactivates abscisic acid to cause seeds to germinate)acid to cause seeds to germinate)

EthyleneEthylene Gas – causes fruit ripening (breakdown of starch to Gas – causes fruit ripening (breakdown of starch to

sugar, breakdown of cell walls to soften, chlorophyll sugar, breakdown of cell walls to soften, chlorophyll breaks down)breaks down)

Inhibits axillary growth in response to high auxinInhibits axillary growth in response to high auxin Causes leaf death in winter (can’t get water from Causes leaf death in winter (can’t get water from

frozen ground – don’t want to lose waterfrom leaves)frozen ground – don’t want to lose waterfrom leaves) Produced also in response to stress (drought, flood, Produced also in response to stress (drought, flood,

infection)infection) Destroys inside of xylem to make hollow tubesDestroys inside of xylem to make hollow tubes Plant growth in sprouting plant – when hits Plant growth in sprouting plant – when hits

something solid – secretes ethylene – plant grows something solid – secretes ethylene – plant grows horizontally to escape object then turns upward againhorizontally to escape object then turns upward again

BrassinosteriodsBrassinosteriods

Cells elongation and division in stem (like Cells elongation and division in stem (like auxin)auxin)

Prevents leaves from falling offPrevents leaves from falling off

Promotes root growth at low conc. and stops Promotes root growth at low conc. and stops root growth at high concentrationsroot growth at high concentrations

Circadian RhythmsCircadian Rhythms

Fluctuations based on a 24 hour cycle – not Fluctuations based on a 24 hour cycle – not due to environmental stimuli – based on some due to environmental stimuli – based on some internal time clockinternal time clock

Devoid of environmental clues – it deviates Devoid of environmental clues – it deviates slightly from the 24 hour cycle (vary from 21-slightly from the 24 hour cycle (vary from 21-27 hours)27 hours)

External Signaling in PlantsExternal Signaling in PlantsLight, Gravity, Mechanical StimuliLight, Gravity, Mechanical Stimuli

Phototropism – growing toward sun (Auxin)Phototropism – growing toward sun (Auxin) Gravitropism – roots grow down, stems grow up (Auxin)Gravitropism – roots grow down, stems grow up (Auxin) Thigmotropism – change in growth due to mechanical stress Thigmotropism – change in growth due to mechanical stress

(vines grow straight until contact – wrap around due to (vines grow straight until contact – wrap around due to differential growth on opposite sides)differential growth on opposite sides)

Rapid Leaf Movements – loss of K+ causes water loss and Rapid Leaf Movements – loss of K+ causes water loss and leaves to fold upleaves to fold up

Sleep movements – transport K+ from 1 side of leaf to another Sleep movements – transport K+ from 1 side of leaf to another – changing water flow– changing water flow

Rubbing or touching a plant changes gene expression – can Rubbing or touching a plant changes gene expression – can make plants shorter by rubbing the stem a couple of times a make plants shorter by rubbing the stem a couple of times a dayday

Plant response to lightPlant response to light Two types of light receptorsTwo types of light receptors

Blue light receiversBlue light receivers Phytochromes – receive red light – photoreceptor Phytochromes – receive red light – photoreceptor

linked to a kinaselinked to a kinase Photoperiodism – control of flowering and leaf Photoperiodism – control of flowering and leaf

growth by length of daysgrowth by length of days Short Day/Long Night – flower when light is Short Day/Long Night – flower when light is

shorter than a critical length (flower late summer)shorter than a critical length (flower late summer) Long Day/Short Night – flower when light is Long Day/Short Night – flower when light is

longer than a critical length (flower in spring)longer than a critical length (flower in spring) Controlled by phytochromes – bound to a light Controlled by phytochromes – bound to a light

absorbing molecule – light changes shape of absorbing molecule – light changes shape of phytochrome which change cellular responses)phytochrome which change cellular responses)

Plant Response to StressPlant Response to Stress Lack of WaterLack of Water

activate abscisic acid = K+ leaves and so does water – activate abscisic acid = K+ leaves and so does water – guard cells closeguard cells close

Leaf growth inhibited due to lack of turgor pressure, so less Leaf growth inhibited due to lack of turgor pressure, so less water lostwater lost

Lack of Oxygen (from overwatering – reduces air in Lack of Oxygen (from overwatering – reduces air in soil)soil) Some form air tubes in roots (ethylene causes cell death in Some form air tubes in roots (ethylene causes cell death in

ground cells in roots forming tubes, or roots are out of soil)ground cells in roots forming tubes, or roots are out of soil) Too much salt (causes water deficit)Too much salt (causes water deficit)

Make internal solutes to deep water potential lower in plantMake internal solutes to deep water potential lower in plant Heat (enzymes denature, water evaporatesHeat (enzymes denature, water evaporates

Transpiration for evaporative coolingTranspiration for evaporative cooling Make heat shock proteins – may help prevent denaturation Make heat shock proteins – may help prevent denaturation

of proteinsof proteins

Plant Response to Stress ContinuedPlant Response to Stress Continued ColdCold

Plants increase amt. of unsat. Fatty acids in membrane to make them Plants increase amt. of unsat. Fatty acids in membrane to make them more fluidmore fluid

Change solute concentration in cells to prevent cooling with out ice Change solute concentration in cells to prevent cooling with out ice crystals forming in cellscrystals forming in cells

HerbivoresHerbivores Physical defenses – thorns, stickersPhysical defenses – thorns, stickers Chemical toxins (ex. Make a weird aa that when incorporated into Chemical toxins (ex. Make a weird aa that when incorporated into

insect proteins – proteins are misshapen and the insects die) (ex. 2 – insect proteins – proteins are misshapen and the insects die) (ex. 2 – plant sends chemical signal in response to damage – signal causes plant sends chemical signal in response to damage – signal causes wasps to come and inject eggs into catepillars eating the plant, wasp wasps to come and inject eggs into catepillars eating the plant, wasp babies eat their way out)babies eat their way out)

InfectionsInfections Tough epidermisTough epidermis Phytoalexins and PR proteins – kill bacteria by dissolving their cell Phytoalexins and PR proteins – kill bacteria by dissolving their cell

wallswalls Express defense genes – apoptosis of infected cells, produce antibioticsExpress defense genes – apoptosis of infected cells, produce antibiotics Produce Salicylic Acid – makes cells resistant to attackProduce Salicylic Acid – makes cells resistant to attack