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Seed germination Seeds remain dormant until sense appropriate conditions:

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

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Seed germination Seeds remain dormant until sense appropriate conditions:

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  1. 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

  2. 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 & pO2

  3. 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

  4. 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

  5. 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

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

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

  8. Light regulation of growth • Plants sense • Light quantity • Light quality (colors) • Light duration • Direction it comes from Have photoreceptors that sense specific wavelengths

  9. 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

  10. 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

  11. 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!

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

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

  14. 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!

  15. 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

  16. 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

  17. 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

  18. 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 Made as inactive cytoplasmic Pr that absorbs at 666 nm

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

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

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

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

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

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

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

  26. 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

  27. 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

  28. Types of Phytochrome Responses Two categories based on speed 3 classes based on fluence (amount of light needed) VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2

  29. Types of Phytochrome Responses • Two categories based on speed 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2 • Changes 0.02% of Pr to Pfr

  30. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2 • Changes 0.02% of Pr to Pfr • Are not FR-reversible!

  31. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2 • Changes 0.02% of Pr to Pfr • Are not FR-reversible! But action spectrum same as Pr

  32. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2 • Changes 0.02% of Pr to Pfr • Are not FR-reversible! But action spectrum same as Pr • Induced by FR!

  33. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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

  34. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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 Examples: Cab gene induction, oat coleoptile growth

  35. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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 Examples: Cab gene induction, oat coleoptile growth 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2

  36. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2 Are FR-reversible!

  37. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2 Are FR-reversible! Need > 3% Pfr

  38. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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

  39. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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

  40. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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 3. HIR: require prolonged exposure to higher fluence

  41. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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

  42. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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!

  43. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) • VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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!

  44. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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

  45. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/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 Different responses = Different phytochromes

  46. Types of Phytochrome Responses 3 classes based on fluence (amount of light needed) VLF:induced by 0.1 nmol/m-2 , saturate @ 50nmol/m-2 2. LF: induced by 1 µmol/m-2, saturate @ 1000 µmol/m-2 3. HIR: require prolonged exposure to higher fluence Different responses = Different phytochromes: 3 in rice, 5 in Arabidopsis

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

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

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

  50. Types of Phytochrome Responses • 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

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