photomorphogenesis control of growth development by light
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Photomorphogenesis (control of growth & development by light). Environmental signals (light, temperature and gravity) are important signals for plant development Light affects many aspects of plant development, for example: required for proper leaf development

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photomorphogenesis control of growth development by light
Photomorphogenesis(control of growth & development by light)
  • Environmental signals (light, temperature and gravity) are important signals for plant development
  • Light affects many aspects of plant development, for example:
    • required for proper leaf development
    • inhibits stem elongation in the emerging seedling
    • promotes flowering (photoperiodism)
    • promotes (or inhibits) seed germination
molecular biol of leaf development
Molecular Biol. of Leaf Development

Arabidopsis

Dark-grown

Light-grown

  • Leaf development is light-dependent in angiosperms
  • Chloroplast development is the signature feature:

proplastids > (etioplasts) >chloroplasts

(plastid number per cell increases)

  • Light controls expression of important chloroplast proteins

cotyledon

hypocotyl

Skotomorphogenesis – seedling development in darkness

slide3

Barley (Hordeum vulgare) 7-10 days old

Older cells (etioplasts)

light

Young cells w/proplastids

slide4

CF1- α, β subunits of ATP synthetase

PSI - photosystem I Chl-apoproteins

PSII – photosystem II Chl-apoproteins

Pchlrd – protochlorophyllide reductase

LHCII- light-harvesting Chl-apoproteins of PSII

LS - large subunit of RuBPCase

SS – small subunit of RuBPCase

From J. Mullet & colleagues

slide5

several steps light + NADPH

aminolevulinic acid -------------> protochlorophyllide  Chlorophyllide  Chl Pchlrd

Step in chlorophyll synthesis that requires light

Pchlrd (Protochlorophyllide reductase) – enzyme that catalyzes the reduction of protochlorophyllide; it over-accumulates in dark-grown plants, and is down-regulated by light.

Protochlorophyllide

Chlorophyllide

slide6

Protein synthesis and select mRNA levels in plastids from dark-grown barley and after illumination.

D – psbA gene product, other proteins were described in a preceding slide

From J. Mullet & colleagues

regulation of plastid proteins by light
Regulation of Plastid Proteins by Light

1. Light induction of the chloroplast-encoded proteins is mainly at the translational and post-translational (i.e., protein stability) levels

John Mullet

slide8

Nuclear-encoded Cab/lhc mRNAs are not present in dark-grown plants. They are induced by white light or pulses of red light, & inhibited by pulses of far-red light.

N-H. Chua and colleagues

slide9

Transcription run-off in isolated nuclei of selected genes from dark-grown barley, and after the indicated light treatments.

rbcS – small subunit of RuBPCase

cab/lhc – light-harvesting Chl- apoproteins of PSII

pcr- protochlorophyliide reductase

Klaus Apel

regulation of plastid proteins by light1
Regulation of Plastid Proteins by Light

1. Light induction of the chloroplast-encoded proteins is mainly at the translational and post-translational (i.e., protein stability) levels

2. Regulation of the nuclear-encoded genes (e.g., rbcS, cab/lhc, and pcr ) is mainly at transcription

- light can down-regulate (pcr) as well as up-regulate

- transcriptional control also mediated by Phytochrome

how does light control gene transcription and plastid development t he photoreceptor s
How does light control gene transcription and plastid development ?: The photoreceptor(s)
  • Plants See:
  • Light Intensity
  • Light Direction
  • Colors
slide13
PHYTOCHROME (PHY)

Some major phytochrome-controlled processes:

  • Surface seed germination
  • Inhibition of stem elongation in young seedlings
  • Promoting leaf development in young seedlings
  • promotes stomatal opening

Phy exists in two interconvertible forms:

Pr- inactive, absorbs mainly red light (660 nm)

Pfr- active, absorbs far-red light (730 nm)

Pfr Pr slowly in dark

slide14

More Phytochrome properties :

  • Protein subunit of 125,000 Daltons (~1100 amino acids).
  • Chromophore is a linear tetrapyrrole, attached covalently to a cysteine.
  • Native Phy is a dimer.
  • Has His-kinase activity.

The “Red Far-Red” test for Phy control:

Pulse of red light  response

Pulse of far-red light no response

Pulse of red lightpulse of far-redno response

slide15

Phytochrome in Arabidopsis

- 5 Phytochrome (PhyA-PhyE) genes

- Have overlapping functions, based on mutant analysis

- Vary with respect to the light intensity or light quality required for activation:

- e.g., far-red responses are mediated by Phy A

- Can form heterodimers

slide16

Blue-light receptor for leaf development

(Blue light promotes leaf development and phototropsim)

  • absorb in the 350-450 nm range
  • a.k.a. Cryptochrome
  • Cryptochrome gene (Cry) identified using genetic approach (Cashmore & colleagues):

- hy4 mutant of Arabidopsis

  • chromophore = flavin (FAD)

Tony Cashmore

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