Seed germination Seeds remain dormant until sense appropriate

Seed germination Germination is a two step process • Imbibition is purely physical: seed

Vegetative growth Once radicle has emerged, vegetative growth begins • Juvenile plants in light

Vegetative growth Once radicle has emerged, vegetative growth begins • Add new leaves @

Transition to Flowering Adults are competent to flower, but need correct signals Very complex

Light regulation of Plant Development Plants use light as food and information Use information

Light regulation of Plant Development • Germination • Morphogenesis • Sun/shade & shade avoidance

Light regulation of growth Plants sense 1. Light quantity 2. Light quality (colors) 3.

Light regulation of growth Duration = photoperiodism (Garner and Allard, 1920) Maryland Mammoth tobacco

Light regulation of growth Measures night! 30" flashes during night stop flowers LDP plants

Phytochrome Next : color matters! Red light (666 nm)works best for flowering & for

Phytochrome But, Darwin showed blue works best for phototropism! Different photoreceptor! Red light (666

Phytochrome Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination

Phytochrome Red light (666 nm) promotes germination Far red light (730 nm) blocks germination

Phytochrome Made as inactive cytoplasmic Pr that absorbs at 666 nm or in blue

Types of Phytochrome Responses Two categories based on speed 1. Rapid biochemical events 2.

Types of Phytochrome Responses Lag time also varies from minutes to weeks: numbers of

Types of Phytochrome Responses Two categories based on speed 3 classes based on fluence

Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) 1.

Types of Phytochrome Responses Different responses = Different phytochromes: 3 in rice, 5 in

Types of Phytochrome Responses 1. PHYA mediates VLF and HIR due to FR •

Types of Phytochrome Responses PHYA & PHYB are often antagonistic. In sunlight PHYB mainly

Phytochrome Pr has cis-chromophore Red converts it to trans = active shape

Phytochrome Pr has cis-chromophore Red converts it to trans = active shape Far-red reverts

Phytochrome Pfr is a protein kinase: acts by kinasing key proteins • some stays

Phytochrome Pfr is a protein kinase: acts by kinasing key proteins • some stay

Phytochrome stay in cytoplasm & activate ion pumps • Rapid responses are due to

Phytochrome most enter nucleus and kinase transcription factors • Slow responses are due to

• • Phytochrome Slow responses are due to changes in gene expression Many

• • • Phytochrome Slow responses are due to changes in gene expression

Phytochrome • 20% of genes are light-regulated • Protein degradation is important for light

Phytochrome • Protein degradation is important for light regulation • Cop mutants can’t degrade

• • • Phytochrome Protein degradation is important for light regulation Cop mutants

Phytochrome • COPs target specific TF for degradation • W/O COPs they act in

Slides: 73

Download presentation

Seed germination Seeds 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 germination Germination 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 & p. O 2

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

Vegetative growth Once 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

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

Light regulation of Plant Development Plants use light as food and information Use information to control development

Light regulation of Plant Development • Germination • Morphogenesis • Sun/shade & shade avoidance • Flowering • Senescence

Light regulation of growth Plants sense 1. Light quantity 2. Light quality (colors) 3. Light duration 4. Direction it comes from Have photoreceptors that sense specific wavelengths

Light regulation of growth Duration = 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 LDP plants such as Arabidopsis need long days to flower SDP flower in fall, LDP flower in spring, neutral flower when ready

Light regulation of growth Measures night! 30" flashes during night stop flowers LDP plants such as Arabidopsis need long days to flower SDP flower in fall, LDP flower in spring, neutral flower when ready Next : color matters! Red light works best for flowering

Phytochrome Next : 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!

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

Phytochrome Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination After alternate R/FR flashes last flash decides outcome

Phytochrome Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination After alternate R/FR flashes last flash decides outcome Seeds don't want to germinate in the shade!

Phytochrome Red light (666 nm) promotes germination Far red light (>700 nm) blocks germination After alternate R/FR color of final flash decides outcome Seeds don't want to germinate in the shade! Pigment is photoreversible

Phytochrome Red light (666 nm) promotes germination Far red light (730 nm) blocks germination After alternate R/FR color of final flash decides outcome Pigment is photoreversible! -> helped purify it! Looked for pigment that absorbs first at 666 nm, then 730

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

Phytochrome Made as inactive cytoplasmic Pr that absorbs at 666 nm or in blue Converts to active Pfr that absorbs far red (730 nm) 97% of Pfr is converted back to Pr by far red light

Phytochrome Made as inactive cytoplasmic Pr that absorbs at 666 nm or in blue Converts to active Pfr that absorbs far red (730 nm) 97% of Pfr is converted back to Pr by far red light Also slowly reverts in dark

Types of Phytochrome Responses Two categories based on speed 1. Rapid biochemical events 2. Morphological changes

Types of Phytochrome Responses Two categories based on speed 1. Rapid biochemical events 2. Morphological changes Lag time also varies from minutes to weeks

Types of Phytochrome Responses Two categories based on speed 1. Rapid biochemical events 2. Morphological changes Lag time also varies from minutes to weeks: numbers of steps after Pfr vary

Types of Phytochrome Responses Lag time also varies from minutes to weeks: numbers of steps after Pfr vary "Escape time" until a response can no longer be reversed by FR also varies

Types of Phytochrome Responses Lag time also varies from minutes to weeks: numbers of steps after Pfr vary "Escape time" until a response can no longer be reversed by FR also varies: time taken for Pfr to do its job Conclusions: phytochrome acts on many processes in many ways

Types of Phytochrome Responses Two categories based on speed 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2

Types of Phytochrome Responses Two categories based on speed 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2 • Changes 0. 02% of Pr to Pfr

Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2 • Changes 0. 02% of Pr to Pfr • Are not FR-reversible!

Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2 • Changes 0. 02% of Pr to Pfr • Are not FR-reversible! But action spectrum same as Pr • Induced by FR! Obey law of reciprocity: 1 nmol/m-2 x 100 s = 100 nmol/m-2 x 1 sec

Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2 Are FR-reversible! Need > 3% Pfr Obey law of reciprocity Examples : Lettuce seed Germination, mustard photomorphogenesis, inhibits flowering in SDP

Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2 3. HIR: require prolonged exposure to higher fluence Effect is proportional to fluence Disobey law of reciprocity Are not FR-reversible! Some are induced by FR!

Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2 3. HIR: require prolonged exposure to higher fluence Effect is proportional to fluence Disobey law of reciprocity Are not FR-reversible! Some are induced by FR! Examples: inhibition of hypocotyl elongation in many seedlings, Anthocyanin synthesis

Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) 1. VLF: induced by 0. 1 nmol/m-2 , saturate @ 50 nmol/m-2 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2 3. HIR: require prolonged exposure to higher fluence Effect is proportional to fluence Disobey law of reciprocity Are not FR-reversible! Some are induced by FR! Examples: inhibition of hypocotyl elongation in many seedlings, Anthocyanin synthesis 1. Different responses = 2. Different phytochromes

Types of Phytochrome Responses Different responses = Different phytochromes: 3 in rice, 5 in Arabidopsis 1. PHYA mediates VLF and HIR due to FR

Types of Phytochrome Responses Different responses = Different phytochromes: 3 in rice, 5 in Arabidopsis 1. PHYA mediates VLF and HIR due to FR • Very labile in light

Types of Phytochrome Responses Different responses = Different phytochromes: 3 in rice, 5 in Arabidopsis 1. PHYA mediates VLF and HIR due to FR • Very labile in light 2. PHYB mediates LF and HIR due to R • Stable in light

Types of Phytochrome Responses 1. PHYA mediates VLF and HIR due to FR • Very labile in light 2. PHYB mediates LF and HIR due to R • Stable in light 3. Roles of PHYs C, D & E not so clear

Types of Phytochrome Responses 1. PHYA mediates VLF and HIR due to FR • Very labile in light 2. PHYB mediates LF and HIR due to R • Stable in light 3. Roles of PHYs C, D & E not so clear PHYA & PHYB are often antagonistic.

Types of Phytochrome Responses PHYA & PHYB are often antagonistic. In sunlight PHYB mainly controls development

Types of Phytochrome Responses PHYA & PHYB are often antagonistic. In sunlight PHYB mainly controls development In shade PHYA 1 st controls development, since FR is high

Types of Phytochrome Responses PHYA & PHYB are often antagonistic. In sunlight PHYB mainly controls development In shade PHYA 1 st controls development, since FR is high But PHYA is light-labile; PHYB takes over & stem grows "shade-avoidance"

Phytochrome Pr has cis-chromophore

Phytochrome Pr has cis-chromophore Red converts it to trans = active shape

Phytochrome Pr has cis-chromophore Red converts it to trans = active shape Far-red reverts it to cis

Phytochrome Pfr is a protein kinase: acts by kinasing key proteins • some stays in cytoplasm & activates ion pumps

Phytochrome Pfr is a protein kinase: acts by kinasing key proteins • some stays in cytoplasm & activates ion pumps • Rapid responses are due to changes in ion fluxes

Phytochrome Pfr is a protein kinase: acts by kinasing key proteins • some stays in cytoplasm & activates ion pumps • Rapid responses are due to changes in ion fluxes • Increase growth by activating PM H+ pump

Phytochrome Pfr is a protein kinase: acts by kinasing key proteins • some stay in cytoplasm & activate ion pumps • Rapid responses are due to changes in ion fluxes • most enter nucleus and kinase transcription factors

Phytochrome stay in cytoplasm & activate ion pumps • Rapid responses are due to changes in ion fluxes most enter nucleus and kinase transcription factors • Slow responses are due to changes in gene expression

Phytochrome most enter nucleus and kinase transcription factors • Slow responses are due to changes in gene expression • Many targets of PHY are transcription factors, eg PIF 3

Phytochrome most enter nucleus and kinase transcription factors • Slow responses are due to changes in gene expression • Many targets of PHY are transcription factors, eg PIF 3 • Activate cascades of genes for photomorphogenesis

• • Phytochrome Slow responses are due to changes in gene expression Many targets of PHY are transcription factors, eg PIF 3 Activate cascades of genes for light responses Some overlap, and some are unique to each phy

• • • Phytochrome Slow responses are due to changes in gene expression Many targets of PHY are transcription factors, eg PIF 3 Activate cascades of genes for light responses Some overlap, and some are unique to each phy 20% of genes are light-regulated

Phytochrome • 20% of genes are light-regulated • Protein degradation is important for light regulation

Phytochrome • 20% of genes are light-regulated • Protein degradation is important for light regulation • Cop mutants can’t degrade specific proteins

Phytochrome • Protein degradation is important for light regulation • Cop mutants can’t degrade specific proteins • COP 1/SPA targets specific transcription factors for degradation

Phytochrome • Protein degradation is important for light regulation • Cop mutants can’t degrade specific proteins • COP 1/SPA targets specific TF for degradation • DDA 1/DET 1/COP 10 target other proteins for degradation

• • • Phytochrome Protein degradation is important for light regulation Cop mutants can’t degrade specific proteins COP 1/SPA targets specific TF for degradation DDA 1/DET 1/COP 10 target other proteins Other COPs form part of COP 9 signalosome W/O COPs these TF act in dark

Phytochrome • COPs target specific TF for degradation • W/O COPs they act in dark • In light COP 1 is exported to cytoplasm so TF can act • Tags PHYA by itself on the way out!