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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
