Download PHOTOMORPHOGENESIS

I.
Influence of light on plant growth and development
A.
II.
How do plants grown in light differ from plants grown in the
dark?
1.
Chlorophyll production promoted by light.
2.
Leaf expansion promoted by light.
3.
Stem elongation inhibited by light.
4.
Root development promoted by light.
5.
Need a photoreceptor
Discovery of Phytochrome
A.
Etiolated Seedling Growth
1.
B.
Brief exposure to light results in de-etiolation
a)
Leaves expand
b)
Hook opens
c)
Rate of stem elongation slows
Lettuce seed germination
1.
Action spectrum showed that red light promoted and
far-red inhibited
2.
Far-red could also counter red light exposure.
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3.
C.
Suggested that single pigment is photo-reversible and
changes absorption characteristics
Flowering
1.
2.
Garner and Allard
a)
The concept of photoperiod
b)
Getting Maryland Mammoth tobacco to flower
Cockleburs need SD too - but
a)
Interrupt night with light and no flowers
(1)
Red light most effective wavelength
Day Length is most reliable indication and predictor of advancing
seasons.
I.
Photoperiodism important in:
A.
Flowering
B.
Seed germination
1.
C.
Birch seeds require long days
Tuber development
1.
Potato SD
D.
Tillering
E.
Leaf fall and bud dormancy
1.
SD response
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II.
Photoperiodic Response types
A.
Three fundamental categories
1.
Short-day plants (SD)
a)
Respond (flower) when day length shorter than
some critical value within 24-hour period.
(1)
Qualitative (obligate)
(a)
(2)
Cocklebur (Xanthium) must have at
least one SD photoperiod
(CV < 15.5)
Quantitative (facultative)
(a)
2.
Hemp (Cannabis sativa) will flower
and produce more flowers if given a
number of cycles of SD.
Long-day plants (LD)
a)
Respond (flower) when day length longer than
some critical value within 24-hour period.
(1)
Qualitative (obligate)
(a)
(2)
Black henbane (Hyoscyamus niger)
needs day-lengths > 11 hours
Quantitative (facultative)
(a)
Flowering is accelerated in spring
wheat (Triticum) with LD even
though it will eventually flower
under SD.
(i) 7 lvs verses 22 lvs.
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3.
Day-neutral plants (DNP)
a)
III.
No day length requirement
When DAY really means NIGHT
A.
SD Cocklebur experiments
1.
2.
3.
4.
5.
15.5 hr light 8.5 hr dark
16 hr light / 8 hr dark
4 hr light / 8 hr dark
4 hr light / 9 hr dark
16 hr light / 32 hr dark
FLOWERS
NO FLOWERS
NO FLOWERS
FLOWERS
FLOWERS
What do you conclude?
6.
Follow-up experiments
a)
b)
B.
15 hr light / 9 hr dark w/light interrupt
NO FLOWERS
16 hr light w/dark interrupt / 8 hr dark
NO FLOWERS
Long day plant experiments
1.
15 hr light / 9 hr dark
FLOWERS
2.
9 hr light / 15 hr dark
NO FLOWERS
3.
9 hr light / 15 hr dark w/light interrupt
FLOWERS
What do you conclude?
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SUMMARY
III.
Characteristics of Phytochrome
A.
Chromoprotein
1.
Chromophore is open chain tetrapyrrole similar to
phycocyanin linked to protein.
2.
Chromophore absorbs the light!
3.
Think both chromophore and apoprotein undergo
conformational change in interconversion.
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4.
B.
Found in membranes of endoplasmic reticulum and
plasma membrane but not chloroplasts or mitochondria.
Two mutually photo-reversible forms
1.
Phytochrome red form (Pr)
a)
Blue pigment
b)
Absorbs red light maximally at 660 nm
(1)
c)
2.
Also in blue region
Converted to Pfr
Phytochrome far-red form (Pfr)
a)
Olive green pigment
b)
Absorbs light maximally at 730 nm
(1)
c)
Also in red and blue region
Converted to Pr
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