Seeds Seeds are unique feature of plants. Seeds Seeds are unique feature of plants Plant dispersal units.

SeedsSeeds are unique feature of plants

SeedsSeeds are unique feature of plants• Plant dispersal units

SeedsSeeds are unique feature of plants• Plant dispersal units• Must survive unfavorableconditions until they reach suitable place (and time) to start next generation

SeedsSeeds are unique feature of plants• Plant dispersal units• Must survive unfavorable conditions until they reach suitable place (and time) to start next generation• Are dormant

SeedsSeeds are unique feature of plants• Plant dispersal units• Must survive unfavorable conditions until they reach suitable place (and time) to start next generation• Are dormant; dehydration is key

SeedsSeeds are unique feature of plants• Plant dispersal units• Must survive unfavorable conditions until they reach suitable place (and time) to start next generation• Are dormant; dehydration is key

• Germinate when conditions are right

SeedsGerminate when conditions are right• Need way to sense conditions while dormant

SeedsGerminate when conditions are right• Need way to sense conditions while dormant• Need reserves to nourish seedling until it is

established

Seeds(Usually) required for fruit development!

Seeds(Usually) required for fruit development!Role of fruit is to aid seed dispersal!

Seed Development(Usually) required for fruit development!Role of fruit is to aid seed dispersal!• Unfertilized flowers don’t develop fruit

Seed Development(Usually) required for fruit development!Role of fruit is to aid seed dispersal!• Unfertilized flowers don’t develop fruits• The growth regulators GA, auxin or cytokinin can all

induce parthenocarpy

Seed Development(Usually) required for fruit development!Role of fruit is to aid seed dispersal!• Unfertilized flowers don’t develop fruits• The growth regulators GA, auxin or cytokinin can all

induce parthenocarpy• GA + auxin or GA + cytokinin work best

Seed Development(Usually) required for fruit development!Role of fruit is to aid seed dispersal!• Unfertilized flowers don’t develop fruits• The growth regulators GA, auxin or cytokinin can all

induce parthenocarpy• GA + auxin or GA + cytokinin work best

• Hormones from embryo stimulate fruit development

Seed DevelopmentHormones from embryo stimulate fruit developmentOther floral organs make inhibitor that blocks fruit

development until they abscise

Seed DevelopmentHormones from embryo stimulate fruit developmentOther floral organs make inhibitor that blocks fruit

development until they absciseDivide seed development into three phases of ± equal time

Seed DevelopmentDivide seed development into three phases of ± equal time1. Morphogenesis

Seed DevelopmentDivide seed development into three phases of ± equal time1. Morphogenesis2. Maturation

Seed DevelopmentDivide seed development into three phases of ± equal time1. Morphogenesis2. Maturation3. Dehydration and dormancy

Seed Development End result is seed with embryo packaged inside protective

coat

Seed Development End result is seed with embryo packaged inside protective

coat• Seed coat is maternal tissue!

Seed Development End result is seed with embryo packaged inside protective

coat• Seed coat is maternal tissue!• Derived from epidermal tissue surrounding ovule

Seed Development Seed coat is maternal tissue!• Derived from epidermal tissue surrounding ovule• Determines shape of the seed!

Seed Development Seed coat is maternal tissue!• Derived from epidermal tissue surrounding ovule• Determines shape of the seed!• Testa mutants have odd-shaped seeds

Seed Development Seed coat is maternal tissue!• Derived from epidermal tissue surrounding ovule• Determines shape of the seed!• Testa mutants have odd-shaped seeds • embryo grows to fill shape set by testa!

Seed Development End result is seed with embryo packaged inside protective

coatEndosperm feeds developing embryo (3n grows faster)

Seed Development End result is seed with embryo packaged inside protective

coatEndosperm feeds developing embryo (3n grows faster)In many dicots endosperm is absorbed as seed develops

Seed Development End result is seed with embryo packaged inside protective

coatEndosperm feeds developing embryo (3n grows faster)In many dicots endosperm is absorbed as seed develops• Often leave a thin layer of endosperm just inside testa

Seed Development End result is seed with embryo packaged inside protective

coatEndosperm feeds developing embryo (3n grows faster)In many dicots endosperm is absorbed as seed develops• Often leave a thin layer of endosperm just inside testa• Seeds have three different genetic compositions!

Seed Development End result is seed with embryo packaged inside protective

coatEndosperm feeds developing embryo (3n grows faster)In many dicots endosperm is absorbed as seed developsIn many monocots endosperm is seedling food

Seed Development 1. Embryogenesis2. Maturation: cell division ± ceases, but cells still expand

Seed Development 1. Embryogenesis2. Maturation: cell division ± ceases, but cells still expand• Controlled by different genes: viviparous mutants have

normal morphogenesis but don’t mature

Seed Development 1. Embryogenesis2. Maturation: cell division ± ceases, but cells still expand• Controlled by different genes: viviparous mutants have

normal morphogenesis but don’t mature• Many morphogenesis mutants show normal maturation

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds• ABA made by maternal tissue initiates this process

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds• ABA made by maternal tissue initiates this process• Seed [ABA] increases as enter maturation phase

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds• ABA made by maternal tissue initiates this process• Seed [ABA] increases as enter maturation phase• Switch to ABA synthesis by embryo & endosperm

during maturation

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds• Storage compounds are key for seedlings and crops

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds• Storage compounds are key for seedlings and crops• Proteins, lipids & carbohydrates but vary widely

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds• Storage compounds are key for seedlings and crops• Proteins, lipids & carbohydrates but vary widely• Many 2˚ metabolites

Seed Development Maturation: cell division ± ceases, but cells still expand• Activate new genes for making storage compounds• Storage compounds are key for seedlings and crops• Proteins, lipids & carbohydrates but vary widelyNext prepare for desiccation as ABA made by embryo

(+endosperm) increases

Seed Development Next prepare for desiccation as ABA made by embryo

(+endosperm) increasesABA peaks at mid-maturation, then declines (but not to 0)

Seed Development Next prepare for desiccation as ABA made by embryo

(+endosperm) increasesABA peaks at mid-maturation, then declines (but not to 0)Blocks vivipary during maturation

Seed Development Next prepare for desiccation as ABA made by embryo

(+endosperm) increases• Make proteins & other molecules (eg trehalose) that

help tolerate desiccation

Seed Development Next prepare for desiccation as ABA made by embryo

(+endosperm) increases• Make proteins & other molecules (eg trehalose) that

help tolerate desiccationNext dehydrate (to 5% moisture content) and go dormant

Seed Development Next dehydrate (to 5% moisture content) and go dormantVery complex: 2 classes of dormancy

1.1. Coat-imposed Coat-imposed 2.2. embryo dormancyembryo dormancy

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)1.1. Preventing water uptake.Preventing water uptake.

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)1.1. Preventing water uptake.Preventing water uptake.2.2. Mechanical constraint Mechanical constraint

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)1.1. Preventing water uptake.Preventing water uptake.2.2. Mechanical constraint Mechanical constraint 3.3. Interference with gas exchange.Interference with gas exchange.

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)1.1. Preventing water uptake.Preventing water uptake.2.2. Mechanical constraint Mechanical constraint 3.3. Interference with gas exchangeInterference with gas exchange4.4. Retaining inhibitors (ABA)Retaining inhibitors (ABA)

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)1.1. Preventing water uptake.Preventing water uptake.2.2. Mechanical constraint Mechanical constraint 3.3. Interference with gas exchangeInterference with gas exchange4.4. Retaining inhibitors (ABA)Retaining inhibitors (ABA)5.5. Inhibitor production (ABA)Inhibitor production (ABA)

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)1.1. Preventing water uptake.Preventing water uptake.2.2. Mechanical constraint Mechanical constraint 3.3. Interference with gas exchangeInterference with gas exchange4.4. Retaining inhibitors (ABA)Retaining inhibitors (ABA)5.5. Inhibitor production (ABA)Inhibitor production (ABA)Embryo dormancy (Zygotic effect)Embryo dormancy (Zygotic effect)

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)Embryo dormancy (Zygotic effect)Embryo dormancy (Zygotic effect)1.1. Making inhibitors (ABA?)Making inhibitors (ABA?)

Seed Development Coat-imposed Coat-imposed dormancy (maternal effect)Embryo dormancy (Zygotic effect)Embryo dormancy (Zygotic effect)1.1. Making inhibitors (ABA?)Making inhibitors (ABA?)2.2. Absence of activators (GA)Absence of activators (GA)

Seed DevelopmentCoordinated with fruit ripening: fruit’s job is to protect &

disperse seedSeeds remain dormant until sense appropriate conditions:some Lotus germinated after 2000 years!

Seed germinationSeeds remain dormant until sense appropriate conditions:some Lotus germinated after 2000 years!• Water

Seed germinationSeeds remain dormant until sense appropriate conditions:some Lotus germinated after 2000 years!• Water• Temperature: some seeds require vernalization =

prolonged cold spell

Seed germinationSeeds remain dormant until sense appropriate conditions:some Lotus germinated after 2000 years!• Water• Temperature: some seeds require vernalization =

prolonged cold spell• May break down hydrophobic seed coat

Seed germinationSeeds remain dormant until sense appropriate conditions:• Water• Temperature: some seeds require vernalization =

prolonged cold spell• May break down hydrophobic seed coat • May allow inhibitor (eg ABA) to go away

Seed germinationSeeds remain dormant until sense appropriate conditions:• Water• Temperature: some seeds require vernalization =

prolonged cold spell• May break down hydrophobic seed coat • May allow inhibitor (eg ABA) to go away• May allow synthesis of specific RNAs

Seed germinationSeeds remain dormant until sense appropriate conditions:• Water• Temperature: some seeds require vernalization =

prolonged cold spell• May break down hydrophobic seed coat • May allow inhibitor (eg ABA) to go away• May allow synthesis of specific RNAs

• Many require light: says photosynthesis is possible

Seed germinationSeeds remain dormant until sense appropriate conditions:• Water• Temperature: some seeds require vernalization =

prolonged cold spell• Many require light: says photosynthesis is possible• often small seeds with few reserves

Seed germinationSeeds remain dormant until sense appropriate conditions:• Many require light: says that they will soon be able to

photosynthesize: often small seeds with few reserves• Hormones can also trigger (or stop) germination• ABA blocks it• GA stimulates it

Seed germinationSeeds remain dormant until sense appropriate conditions:• Many require light: says that they will soon be able to

photosynthesize: often small seeds with few reserves• Hormones can also trigger (or stop) germination• ABA blocks it• GA stimulates it

Germination is a two step process• Imbibition

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.

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.

• Seeds with endosperm pop testa first, then endosperm

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.

• Seeds with endosperm pop testa first, then endosperm• Separate processes: can pop testa but not endosperm

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.

• Seeds with endosperm pop testa first, then endosperm• Separate processes: can pop testa but not endosperm• Testa and endosperm have different genotypes!

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.• Seeds with endosperm pop testa first, then endosperm• Next embryo must start metabolism and cell elongation

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

Seed germinationGermination is a two step process• Next embryo must start metabolism and cell elongation• This part is sensitive to the environment, esp T & pO2

• Hormones also play a complex role

Seed germinationGermination is a two step process• Next embryo must start metabolism and cell elongation• This part is sensitive to the environment, esp T & pO2

• Hormones also play a complex role• GA, Ethylene and BR all stimulate

Seed germinationGermination is a two step process• Next embryo must start metabolism and cell elongation• This part is sensitive to the environment, esp T & pO2

• Hormones also play a complex role• GA, Ethylene and BR all stimulate• ABA blocks

Seed germinationGermination is a two step process• 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