Plant Growth & Development3 stages1. Embryogenesis

Fertilization to seed

Plant Growth & Development3 stages1. Embryogenesis

Fertilization to seed2. Vegetative growth

Juvenile stageGermination to adult

Plant Growth & Development3 stages1. Embryogenesis

Fertilization to seed2. Vegetative growth

Juvenile stageGermination to adult"phase change" marks transition

Plant Growth & Development3 stages1. Embryogenesis

Fertilization to seed2. Vegetative growth

Juvenile stageGermination to adult"phase change" marks transition

3. Reproductive developmentMake flowers, can reproduce sexually

Sexual reproduction1. haploid gametogenesis in flowers: reproductive organs•Female part = pistil (gynoecium)•Stigma•Style•Ovary •Ovules

Sexual reproduction1. haploid gametogenesis in flowers: reproductive organs•Female part = pistil (gynoecium)•Stigma•Style•Ovary •Ovules

•Male part : anthers•Make pollen

(Wilson & Yang, 2004, Reproduction)

Sexual reproduction1. making haploid gametes in flowers• Pollen = male, 2-3 cells• Made in anther locules

Archesporial cell

Primarysporogenous

cells

Microspores

Pollen mothercells

Primaryparietal

cells

2o parietal cellsEndothecium

Tapetum Middle cell layermeiosis

Sexual reproduction1. making haploid gametes in flowers• Pollen = male, contains 2-3 cells• Made in anthers• Microspores divide to form vegetative cell and germ cell

Sexual reproduction1. making haploid gametes in flowers• Pollen = male, contains 2-3 cells• Made in anthers• Microspores divide to form vegetative cell and germ cell• Germ cell divides to form 2 sperm cells, but often not

until it germinates

Sexual reproduction1. making haploid gametes in flowers• Pollen = male, contains 2-3 cells• Made in anthers• Microspores divide to form vegetative cell and germ cell• Germ cell divides to form 2 sperm cells, but often not

until it germinates• Pollen grains dehydrate and are coated

Sexual reproduction1. making haploid gametes in flowers• Pollen = male, contains 2-3 cells• Made in anthers• Microspores divide to form vegetative cell and germ cell• Germ cell divides to form 2 sperm cells, but often not

until it germinates• Pollen grains dehydrate and are coated

• Are released, reach stigma, then germinate

Sexual reproduction1. making haploid gametes in flowers• Pollen = male, contains 2-3 cells• Egg = female, made in ovaries

Sexual reproduction1. making haploid gametes in flowers• Pollen = male, contains 2-3 cells• Egg = female, made in ovariesMegaspore mother cell → meiosis → 4 haploid megaspores

Sexual reproductionMegaspore mother cell → meiosis → 4 haploid megaspores• 3 die• Functional megaspore divides 3 x w/o cytokinesis

http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT201/Angiosperm/MagnoliophytaLab99/OvuleForm700.jpg

Sexual reproductionMegaspore mother cell → meiosis → 4 haploid megaspores• 3 die• Functional megaspore divides 3 x w/o cytokinesis• Cellularization forms egg, binucleate central cell, 2

synergids & 3 antipodals

http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT201/Angiosperm/MagnoliophytaLab99/OvuleForm700.jpg

Sexual reproductionCellularization forms egg, binucleate central cell, 2

synergids & 3 antipodals• Egg, synergids & central cell are essential

http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT201/Angiosperm/MagnoliophytaLab99/OvuleForm700.jpg

Sexual reproductionCellularization forms egg, binucleate central cell, 2

synergids & 3 antipodals• Egg, synergids & central cell are essential• In many spp antipodals degenerate

http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT201/Angiosperm/MagnoliophytaLab99/OvuleForm700.jpg

Sexual reproduction1. making haploid gametes in flowers2. Pollen lands on stigma & germinates if good signals

Sexual reproduction1. making haploid gametes in flowers2. Pollen lands on stigma & germinates if good signals• Forms pollen tube that grows through style to ovule

Sexual reproductionPollen lands on stigma & germinates if good signals• Forms pollen tube that grows through style to ovule• Germ cell divides to form sperm nuclei

Sexual reproductionPollen lands on stigma & germinates if good signals• Forms pollen tube that grows

through style to ovule• Germ cell divides to form sperm

nucleiPollen tube reaches micropyle& releases sperm nuclei into ovule

Sexual reproductionPollen tube reaches micropyle& releases sperm nuclei into ovuleDouble fertilization occurs!

Sexual reproductionPollen tube reaches micropyle& releases sperm nuclei into ovuleDouble fertilization occurs!One sperm fuses with egg to form zygote

Sexual reproductionPollen tube reaches micropyle& releases sperm nuclei into ovuleDouble fertilization occurs!One sperm fuses with egg to form zygoteOther fuses with central cell to form 3n endosperm

Sexual reproductionPollen tube reaches micropyle& releases sperm nuclei into ovuleDouble fertilization occurs!One sperm fuses with egg to form zygoteOther fuses with central cell to form 3n endospermSynergids play key role in releasing & guiding sperm cells

EmbryogenesisOne sperm fuses with egg to form zygoteOther fuses with central cell to form 3n endospermDevelopment starts immediately!

EmbryogenesisDevelopment starts immediately! Controlled by genes,

auxin & cytokininsApical cell after first division becomes embryo, basal cell

becomes suspensor

EmbryogenesisDevelopment starts immediately! Controlled by genes,

auxin & cytokininsApical cell after first division becomes embryo, basal cell

becomes suspensorKey events1. Establishing polarity: starts @ 1st division

Embryogenesis1. Establishing polarity: starts @ 1st division2. Establishing radial patterning: periclinal divisions form

layers that become dermal, ground & vascular tissue

Embryogenesis1. Establishing polarity: starts @ 1st division2. Establishing radial patterning: periclinal divisions form

layers that become dermal, ground & vascular tissue3. Forming the root and shoot meristems

Embryogenesis1. Establishing polarity: starts @ 1st division2. Establishing radial patterning: periclinal divisions form

layers that become dermal, ground & vascular tissue3. Forming the root and shoot meristems4. Forming cotyledons & roots

Embryogenesis1. Establishing polarity: starts @ 1st division2. Establishing radial patterning: periclinal divisions form

layers that become dermal, ground & vascular tissue3. Forming the root and shoot meristems4. Forming cotyledons & roots Body plan is formed during embryogenesis: seedling that

germinates is a juvenile plant with root and apical meristems

EmbryogenesisEnd result is seed with embryo packaged inside protective

coat

Seed germinationSeeds remain dormant until sense appropriate conditions:• Water• Temperature• Many require light• Some need acid treatment or scarification

• Passage through bird gut• Some need fire

Seed germinationGermination is a two step process• Imbibition is purely physical: seed swells as it absorbs

water until testa pops. Even dead seeds do it.• Next embryo must start metabolism and cell elongation• This part is sensitive to the environment, esp T & pO2

• Once radicle has emerged, vegetative growth begins

Vegetative growthOnce radicle has emerged, vegetative growth begins• Juvenile plants in light undergo photomorphogenesis

Vegetative growthOnce radicle has emerged, vegetative growth begins• Juvenile plants in light undergo photomorphogenesis• Juvenile plants in dark undergo skotomorphogenesisskotomorphogenesis• Seek light: elongate hypocotyl, don’t unfold Seek light: elongate hypocotyl, don’t unfold

cotyledonscotyledons

Vegetative growthOnce radicle has emerged, vegetative growth begins• Juvenile plants in light undergo photomorphogenesis• Expand cotyledons, start making leaves &

photosynthetic apparatus

Vegetative growthOnce radicle has emerged, vegetative growth begins• Juvenile plants in light undergo photomorphogenesis• Expand cotyledons, start making leaves &

photosynthetic apparatus• Initially live off reserves, but soon do net photosynthesis

Vegetative growthOnce radicle has emerged, vegetative growth begins• Initially live off reserves, but soon do net photosynthesis• Add new leaves @ SAM in response

to auxin gradients• Add new branches from axillary

buds lower down stem if apicaldominance wanes

Vegetative growthOnce radicle has emerged, vegetative growth begins• Add new leaves @ SAM in response to auxin gradients• Add new branches from axillary

buds lower down stem if apicaldominance wanes

• Roots grow down seeking water & nutrients

Vegetative growthOnce radicle has emerged, vegetative growth begins• Add new leaves @ SAM in response to auxin gradients• Roots grow down seeking water & nutrients

• 1˚ (taproot) anchors plant• 2˚ roots absorb nutrients

Vegetative growthOnce radicle has emerged, vegetative growth begins• Add new leaves @ SAM in response to auxin gradients• Roots grow down seeking water & nutrients

• 1˚ (taproot) anchors plant• 2˚ roots absorb nutrients

• Continue to add cells by divisions @ RAM

Vegetative growthRoots grow down seeking water & nutrients• Continue to add cells by divisions @ RAM• Form lateral roots in maturation zone in response to

nutrients & auxin/cytokinin

reproductive phaseEventually switch to reproductive phase & start flowering• Are now adults!

reproductive phaseEventually switch to reproductive phase & start flowering•Are now adults!•Triggered by FT protein: moves from leaves to shoot apex in phloem to induce flowering!

Transition to FloweringAdults are competent to flower, but need correct signalsVery complex process!Can be affected by:• Daylength• T (esp Cold)• Water stress• Nutrition• Hormones• Age

reproductive phase• Are now adults!• Very complex process!• Time needed varies from days to years

reproductive phaseEventually switch to reproductive phase & start flowering• Are now adults!• Time needed varies from days to years. • Shoot apical meristem now starts making new organ:

flowers, with many new structures & cell types

SenescenceShoot apical meristem now starts

making new organ: flowers, with many new structures & cell types

Eventually petals, etc senesce = genetically programmed cell death: controlled by specific genes

SenescenceEventually petals, etc senesce = genetically programmed

cell death: controlled by specific genesAlso seen in many other cases: deciduous leaves in fall,

annual plants, older trees

SenescenceInduce specific senescence-associated genes ; eg DNAses,

proteases, lipasesAlso seen during xylem formation: when cell wall is

complete cell kills itself

SenescenceAlso seen during xylem formation: when cell wall is

complete cell kills itselfAlso seen as wound response: hypersensitive responseCells surrounding the wound kill themselves

SenescenceAlso seen during xylem formation: when cell wall is

complete cell kills itselfAlso seen as wound response: hypersensitive responseCells surrounding the wound kill themselvesSome mutants do this w/o wound -> is controlled by genes!

Light regulation of Plant DevelopmentLight regulation of Plant DevelopmentPlants use light as food Plants use light as food andand information informationUse information to control developmentUse information to control development

Light regulation of Plant DevelopmentLight regulation of Plant DevelopmentPlants use light as food Plants use light as food andand information informationUse information to control developmentUse information to control development•germinationgermination

Light regulation of Plant DevelopmentLight regulation of Plant DevelopmentPlants use light as food Plants use light as food andand information informationUse information to control developmentUse information to control development•GerminationGermination•Photomorphogenesis vs skotomorphogenesisPhotomorphogenesis vs skotomorphogenesis

Light regulation of Plant DevelopmentLight regulation of Plant DevelopmentPlants use light as food Plants use light as food andand information informationUse information to control developmentUse information to control development•GerminationGermination•Photomorphogenesis vs skotomorphogenesisPhotomorphogenesis vs skotomorphogenesis•Sun/shade & shade avoidanceSun/shade & shade avoidance

Light regulation of Plant DevelopmentLight regulation of Plant Development•GerminationGermination•MorphogenesisMorphogenesis•Sun/shade & shade avoidanceSun/shade & shade avoidance•FloweringFlowering

Light regulation of Plant DevelopmentLight regulation of Plant Development•GerminationGermination•MorphogenesisMorphogenesis•Sun/shade & shade avoidanceSun/shade & shade avoidance•FloweringFlowering•SenescenceSenescence

Light regulation of growthPlants sense1. Light quantity

Light regulation of growthPlants sense1. Light quantity2. Light quality (colors)

Light regulation of growthPlants sense1. Light quantity2. Light quality (colors)3. Light duration

Light regulation of growthPlants sense1. Light quantity2. Light quality (colors)3. Light duration4. Direction it comes from

Light regulation of growthPlants sense1. Light quantity2. Light quality (colors)3. Light duration4. Direction it comes fromHave photoreceptorsthat sense specific wavelengths

Light regulation of growthEarly work:• Darwin showed that phototropism is controlled by blue light

Light regulation of Plant DevelopmentLight regulation of Plant DevelopmentEarly work:•Darwins : phototropism is controlled by blue light•Duration = photoperiodism (Garner and Allard,1920) Maryland Mammoth tobacco flowers in the S but not in N

Light regulation of Plant DevelopmentLight regulation of Plant DevelopmentEarly work:•Darwins : phototropism is controlled by blue light•Duration = photoperiodism (Garner and Allard,1920) Maryland Mammoth tobacco flowers in the S but not in N= short-day plant (SDP)

Light regulation of Plant DevelopmentLight regulation of Plant DevelopmentDuration = photoperiodism (Garner and Allard,1920) Maryland Mammoth tobacco flowers in the S but not in N= short-day plant (SDP)Measures night! 30" flashes during night stop flowers

Light regulation of growthDuration = photoperiodism (Garner and Allard,1920) Maryland Mammoth tobacco flowers in the S but not in N= short-day plant (SDP)Measures night! 30" flashes during night stop flowersLDP plants such as Arabidopsis need long days to flower

Light regulation of growthDuration = photoperiodism (Garner and Allard,1920) Maryland Mammoth tobacco flowers in the S but not in N= short-day plant (SDP)Measures night! 30" flashes during night stop flowersLDP plants such as Arabidopsis need long days to flowerSDP flower in fall, LDP flower in spring, neutral flower when ready

Light regulation of growthMeasures night! 30" flashes during night stop flowersLDP plants such as Arabidopsis need long days to flowerSDP flower in fall, LDP flower in spring, neutral flower when readyNext : color matters! Red light works best for flowering

Light regulation of growthNext : color matters! Red light (666 nm)works best for flowering & for germination of many seeds!

PhytochromeNext : color matters! Red light (666 nm)works best for flowering & for germination of many seeds!But, Darwin showed blue works best for phototropism!

PhytochromeNext : color matters! Red light (666 nm)works best for flowering & for germination of many seeds!But, Darwin showed blue works best for phototropism!Different photoreceptor!

PhytochromeBut, Darwin showed blue works best for phototropism!Different photoreceptor!Red light (666 nm) promotes germinationFar red light (>700 nm) blocks germination

PhytochromeBut, Darwin showed blue works best for phototropism!Different photoreceptor!Red light (666 nm) promotes germinationFar red light (>700 nm) blocks germination

PhytochromeRed light (666 nm) promotes germinationFar red light (>700 nm) blocks germinationAfter alternate R/FR flashes last flash decides outcome

PhytochromeRed light (666 nm) promotes germinationFar red light (>700 nm) blocks germinationAfter alternate R/FR flashes last flash decides outcomeSeeds don't want to germinate in the shade!

PhytochromeRed light (666 nm) promotes germinationFar red light (>700 nm) blocks germinationAfter alternate R/FR color of final flash decides outcomeSeeds don't want to germinate in the shade!

Pigment is photoreversible

PhytochromeRed light (666 nm) promotes germinationFar red light (730 nm) blocks germinationAfter alternate R/FR color of final flash decides outcomePigment is photoreversible! -> helped purify it!Looked for pigment that absorbs first at 666 nm, then 730

PhytochromeRed light (666 nm) promotes germinationFar red light (730 nm) blocks germinationAfter alternate R/FR color of final flash decides outcomePigment is photoreversible! -> helped purify it!Looked for pigment that absorbs first at 666 nm, then 730

PhytochromeRed light (666 nm) promotes germinationFar red light (730 nm) blocks germinationAfter alternate R/FR color of final flash decides outcomePigment is photoreversible! -> helped purify it!Looked for pigment that absorbs first at 666 nm, then 730Made as inactive cytoplasmic Pr that absorbs at 666 nm

PhytochromeMade as inactive cytoplasmic Pr that absorbs at 666 nm or in blue Converts to active Pfr that absorbs far red (730nm)