Photomorphogenesis (control of growth & development by light)
-
Upload
joseph-richards -
Category
Documents
-
view
57 -
download
1
description
Transcript of 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:
1. required for proper leaf development2. inhibits stem elongation in the emerging seedling3. promotes flowering (photoperiodism)4. promotes (or inhibits) seed germination
Molecular Biol. of Leaf Development
• 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
hypocotyl
cotyledon
Dark-grown Light-grownArabidopsis
Skotomorphogenesis – seedling development in darkness
CF1- α, β subunits of ATP synthetase PSI - photosystem I Chl-apoproteinsPSII – photosystem II Chl-apoproteinsPchlrd – protochlorophyllide reductaseLHCII- light-harvesting Chl-apoproteins of PSII
LS - large subunit of RuBPCaseSS – small subunit of RuBPCase
From J. Mullet & colleagues
several steps light + NADPH aminolevulinic acid -------------> protochlorophyllide Chlorophyllide Chl Pchlrd
Pchlrd (Protochlorophyllide reductase) – enzyme that catalyzes the reduction of protochlorophyllide; it over-accumulates in dark-grown plants, and is down-regulated by light.
Step in chlorophyll synthesis that requires light
Protochlorophyllide Chlorophyllide
D – psbA gene product, other proteins were described in a preceding slide
Protein synthesis and select mRNA levels in plastids from dark-grown barley and after illumination.
From J. Mullet & colleagues
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
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
rbcS – small subunit of RuBPCasecab/lhc – light-harvesting Chl-apoproteins of PSIIpcr- protochlorophyliide reductase
Transcription run-off in isolated nuclei of selected genes from dark-grown barley, and after the indicated light treatments.
Klaus Apel
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 ?: The
photoreceptor(s)
Plants See:- Light Intensity- Light Direction- Colors
PHYTOCHROME (PHY)
Some major phytochrome-controlled processes:1. Surface seed germination2. Inhibition of stem elongation in young seedlings3. Promoting leaf development in young seedlings4. 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
More Phytochrome properties :
1. Protein subunit of 125,000 Daltons (~1100 amino acids).
2. Chromophore is a linear tetrapyrrole, attached covalently to a cysteine.
3. Native Phy is a dimer.4. Has His-kinase activity.
The “Red Far-Red” test for Phy control:Pulse of red light responsePulse of far-red light no responsePulse of red light pulse of far-red no
response
- 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