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)

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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


Photomorphogenesis control of growth development by light

Barley (Hordeum vulgare) 7-10 days old

Older cells (etioplasts)

light

Young cells w/proplastids


Photomorphogenesis control of growth development by light

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


Photomorphogenesis control of growth development by light

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


Photomorphogenesis control of growth development by light

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


Photomorphogenesis control of growth development by light

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


Photomorphogenesis control of growth development by light

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


Photomorphogenesis control of growth development by light

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


Photomorphogenesis control of growth development by light

  • 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


Photomorphogenesis control of growth development by light

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


Photomorphogenesis control of growth development by light

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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