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Understanding Plant Responses to Light for Growth

Explore how plants sense and respond to light, including circadian rhythms, phytochrome effects, and blue light responses for optimal growth and development.

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Understanding Plant Responses to Light for Growth

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  1. Light regulation of growth Plants sense Light quantity Light quality (colors) Light duration Direction it comes from

  2. Types of Phytochrome Responses Two categories based on speed 3 classes based on fluence (amount of light needed)

  3. Circadian rhythms • Many plant responses show circadian rhythms • Once entrained, continue in constant dark, or light! • Gives plant headstart on photosynthesis, other processes that need gene expression

  4. Circadian rhythms Light & TOC1 activate LHY & CCA1 at dawn LHY & CCA1 repress TOC1 in day, so they decline too At night TOC1 is activated (not enough LHY & CCA1) Phytochrome entrains the clock So does blue light

  5. Blue Light Responses • Circadian Rhythms

  6. Blue Light Responses • Circadian Rhythms • Solar tracking

  7. Blue Light Responses Circadian Rhythms Solar tracking Phototropism

  8. Blue Light Responses • Circadian Rhythms • Solar tracking • Phototropism • Inhibiting stem elongation

  9. Blue Light Responses Circadian Rhythms Solar tracking Phototropism Inhibiting stem elongation Chloroplast movement

  10. Blue Light Responses Circadian Rhythms Solar tracking Phototropism Inhibiting stem elongation Chloroplast movement Stomatal opening

  11. Blue Light Responses Circadian Rhythms Solar tracking Phototropism Inhibiting stem elongation Chloroplast movement Stomatal opening Gene expression

  12. Blue Light Responses Circadian Rhythms Solar tracking Phototropism Inhibiting stem elongation Chloroplast movement Stomatal opening Gene expression Flowering in Arabidopsis

  13. Blue Light Responses Circadian Rhythms Solar tracking Phototropism Inhibiting stem elongation Chloroplast movement Stomatal opening Gene expression Flowering in Arabidopsis Responses vary in their fluence requirements

  14. Blue Light Responses Circadian Rhythms Solar tracking Phototropism Inhibiting stem elongation Chloroplast movement Stomatal opening Gene expression Flowering in Arabidopsis Responses vary in their fluence requirements & lag times

  15. Blue Light Responses Responses vary in their fluence requirements & lag time Stomatal opening is reversible by greenlight; others aren’t

  16. Blue Light Responses Responses vary in their fluence requirements & lag time Stomatal opening is reversible by greenlight; others aren’t Multiple blue receptors with different functions!

  17. Blue Light Responses Responses vary in their fluence requirements & lag time Stomatal opening is reversible by greenlight; others aren’t Multiple blue receptors with different functions! Identified by mutants

  18. Blue Light Responses Responses vary in their fluence requirements & lag time Stomatal opening is reversible by greenlight; others aren’t Multiple blue receptors with different functions! Identified by mutants, then clone the gene and identify the protein

  19. Blue Light Responses Responses vary in their fluence requirements & lag time Stomatal opening is reversible by greenlight; others aren’t Multiple blue receptors with different functions! Identified by mutants, then clone the gene and identify the protein Cryptochromes repress hypocotyl elongation

  20. Blue Light Responses Cryptochromes repress hypocotyl elongation Stimulate flowering

  21. Blue Light Responses Cryptochromes repress hypocotyl elongation Stimulate flowering Set the circadian clock (in humans, too!)

  22. Blue Light Responses Cryptochromes repress hypocotyl elongation Stimulate flowering Set the circadian clock (in humans, too!) Stimulate anthocyanin synthesis

  23. Blue Light Responses Cryptochromes repress hypocotyl elongation Stimulate flowering Set the circadian clock (in humans, too!) Stimulate anthocyanin synthesis 3 CRY genes

  24. Blue Light Responses 3 CRY genes All have same basic structure: Photolyase-like domain binds FAD and a pterin (MTHF) that absorbs blue & transfers energy to FAD in photolyase (an enzyme that uses light energy to repair pyr dimers)

  25. Blue Light Responses 3 CRY genes All have same basic structure: Photolyase-like domain binds FAD and a pterin (MTHF) that absorbs blue & transfers energy to FAD in photolyase (an enzyme that uses light energy to repair pyr dimers) DAS binds COP1 & has nuclear localization signals

  26. Blue Light Responses 3 CRY genes All have same basic structure: Photolyase-like domain binds FAD and a pterin (MTHF) that absorbs blue & transfers energy to FAD in photolyase (an enzyme that uses light energy to repair pyr dimers) DAS binds COP1 & has nuclear localization signals CRY1 & CRY2 kinase proteins after absorbing blue

  27. Blue Light Responses 3 CRY genes CRY1 & CRY2 kinase proteins after absorbing blue CRY3 repairs mt & cp DNA!

  28. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable • Triggers rapid changes in PM potential & growth

  29. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable • Triggers rapid changes in PM potential & growth • Opens anion channels in PM

  30. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable • Triggers rapid changes in PM potential & growth • Opens anion channels in PM • Stimulates anthocyanin synthesis

  31. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable • Triggers rapid changes in PM potential & growth • Opens anion channels in PM • Stimulates anthocyanin synthesis • Entrains the circadian clock

  32. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable • Triggers rapid changes in PM potential & growth • Opens anion channels in PM • Stimulates anthocyanin synthesis • Entrains the circadian clock • Also accumulates in nucleus & interacts with PHY & COP1 to regulate photomorphogenesis, probably by kinasing substrates

  33. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable • Triggers rapid changes in PM potential & growth • Opens anion channels in PM • Stimulates anthocyanin synthesis • Entrains the circadian clock • Also accumulates in nucleus & interacts with PHY & COP1 to regulate photomorphogenesis, probably by kinasing substrates 2. CRY2 controls flowering

  34. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable 2. CRY2 controls flowering: little effect on other processes • Light-labile

  35. Blue Light Responses • 3 CRY genes • CRY1 regulates blue effects on growth: light-stable 2. CRY2 controls flowering: little effect on other processes • Light-labile 3. CRY3 enters cp & mito, where binds & repairs DNA!

  36. Blue Light Responses 3 CRY genes CRY1 regulates blue effects on growth 2. CRY2 controls flowering: little effect on other processes CRY3 enters cp & mito, where binds & repairs DNA! Cryptochromes are not involved in phototropism or stomatal opening!

  37. Blue Light Responses Cryptochromes are not involved in phototropism or stomatal opening! Phototropins are!

  38. Blue Light Responses Phototropins are involved in phototropism & stomatal opening! Many names (nph, phot, rpt) since found by several different mutant screens

  39. Phototropins Many names (nph, phot, rpt) since found by several different mutant screens Mediate blue light-induced growth enhancements

  40. Phototropins Many names (nph, phot, rpt) since found by several different mutant screens Mediate blue light-induced growth enhancement & blue light-dependent activation of the plasma membrane H+-ATPase in guard cells

  41. Phototropins Many names (nph, phot, rpt) since found by several different mutant screens Mediate blue light-induced growth enhancement & blue light-dependent activation of the plasma membrane H+-ATPase in guard cells Contain light-activated serine-threonine kinase domain and LOV1 (light-O2-voltage) and LOV2 repeats

  42. Phototropins Many names (nph, phot, rpt) since found by several different mutant screens Mediate blue light-induced growth enhancement & blue light-dependent activation of the plasma membrane H+-ATPase in guard cells Contain light-activated serine-threonine kinase domain and LOV1 (light-O2-voltage) and LOV2 repeats LOV1 & LOV2 bind FlavinMonoNucleotide cofactors

  43. Phototropins Many names (nph, phot, rpt) since found by several different mutant screens Mediate blue light-induced growth enhancement & blue light-dependent activation of the plasma membrane H+-ATPase in guard cells Contain light-activated serine-threonine kinase domain and LOV1 (light-O2-voltage) and LOV2 repeats LOV1 & LOV2 bind FlavinMonoNucleotide cofactors After absorbing blue rapidly autophosphorylate & kinase other proteins

  44. Phototropins After absorbing blue rapidly autophosphorylate & kinase other proteins 1 result = phototropism due to uneven auxin transport

  45. Phototropins After absorbing blue rapidly autophosphorylate & kinase other proteins 1 result = phototropism due to uneven auxin transport Send more to side away from light!

  46. Phototropins After absorbing blue rapidly autophosphorylate & kinase other proteins 1 result = phototropism due to uneven auxin transport Send more to side away from light! Phot 1 mediates LF

  47. Phototropins After absorbing blue rapidly autophosphorylate & kinase other proteins 1 result = phototropism due to uneven auxin transport Send more to side away from light! PHOT 1 mediates LF PHOT2 mediates HIR

  48. Phototropins 2nd result = stomatal opening via stimulation of guard cell PM proton pump Also requires photosynthesis by guard cells!

  49. Phototropins 2nd result = stomatal opening via stimulation of guard cell PM proton pump Also requires photosynthesis by guard cells & signaling from xanthophylls

  50. Phototropins 2nd result = stomatal opening via stimulation of guard cell PM proton pump Also requires photosynthesis by guard cells & signaling from xanthophylls npq mutants don’t make zeaxanthin & lack specific blue response

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