Transcript Phytochrome Action

Phytochrome Action
Plant Physiology 2009
UNI
The pigment phytochrome
• Detects R and FR light
• Provides information about environment
• Answers 3 questions for plant
– Am I in the light?
– Do I have plants as neighbors or above me?
– Is it time to flower?
Seed location?
Red light
from sun
penetrates
to seed.
Seed germinates.
No light
from sun
to this
deep
seed.
No germination.
Red light to seed = near surface
Why bother?
• Seeds store materials to start growth
• Must reach light before running out of
stored materials
• Small seeds
– Need to be very near surface
– Often need light for germination
• Germinating plants straighten & open
leaves at surface, too
Plant neighbors?
Red
absorbed
by other
plants.
Far red reflected
from other plants.
Far red enriched = neighbors
Why does this matter?
• Neighboring plants are threats
– Might grow taller, shade you
• Solution
– Grow at least as tall as neighbors
– Need to know that you have neighbors
• Isolated plants typically shorter than
crowded plants
– Other reasons, too
Under other plants?
Red
absorbed
by other
plants.
Far red
reflected
from other
plants or
transmitted.
Far red enriched = understory
Why important?
• Best growth strategy for understory plants
is different than for plants in open
• Need to know whether
– Shaded by other plants
OR
– Just cloudy
OR
– Late in day (low light)
Right time to flower?
• Unreliable indicators of time of year
– Temperature
– Moisture
– Light levels
• Reliable: length of day/night
– Varies with season
– Varies with latitude
• Detected by phytochrome
Phytochrome has 2 forms
• Red-absorbing phytochrome
Pr
• Far red absorbing phytochrome
Pfr
Pr
Pfr
• Interconverted
• Two forms of the same compound
• Total amount same
In red light
Prfr
Pr absorbs red light,
changes to Pfr form.
Pfr
Pfr doesn’t absorb red
light, stays the same.
In far red light
Pr
Pr doesn’t absorb far red
light, stays the same.
Prfr
Pfr absorbs far red light,
changes to Pr form.
Sunlight
Mostly red
A little far red
In sunlight
Pfrr
Pfrr
Pfr
Pfrr
Pfr
Pfr
Pfrr
Pfr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pfr
In sunlight most P gets converted to Pfr form.
Start of night
Most P in Pfr form.
Pfrr
Pfrr
Pfr
Pfrr
Pfr
Pfr
Pfrr
Pfr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pfr
In the dark
Pfr form changes gradually to Pr form.
Pfrr
Pfr
Prfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Prfr
Pfrr
Prfr
Pfrr
Prfr
After a short night
Pfr still left.
Pfrr
Pfr
Prfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Prfr
Pfrr
Prfr
Pfrr
Prfr
LDP = SNP
• Needs short night
• Needs Pfr still present at end of night
• Pfr promotes flowering for LDPs
Later in the night
More Pfr changes to Pr.
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Pfr
Pfrr
Prfr
Pfrr
Prfr
Pfrr
Pfr
Pfr
Pr
Prfr
Pfrr
Prfr
Pfrr
Prfr
After a long night
All the Pfr is gone.
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Pr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Prfr
Day dawns
Pfrr
Pfrr
Pfr
Pfrr
Pfr
Pfr
Pfrr
Pfr
Pr
Pfr
Pfrr
Pfrr
Prfr
Pfr
Pfr
Pfr
Pfrr
Prfr
Pfrr
Pfr
Most P gets converted to Pfr form again.
SDP = LNP
• Needs long night
• Needs Pfr gone at end of night
• Pfr inhibits flowering for SDPs
LDP
SDP
Long day: Pfr left at end of short night.
Pfr promotes flowering for LDPs.
Pfr inhibits flowering for SDPs.
Short day: Pfr gone at end of long night.
No Pfr to promote flowering for LDPs.
No Pfr to inhibit flowering for SDPs.
Waiting for the right time
• Plants grow leaves until it is time to flower
• LDPs wait until the day is long enough
– Really night short enough
– Some time before June 21
• SPDs wait until the day is short enough
– Really night long enough
– Some time after June 21
• Flower opening happens later
Day neutral plants
• Flower when mature enough
• Maybe other environmental signals (temp?)
• Day length (dark length) doesn’t matter
Through the year
May
Specific
times.
September
Julyflowers at specific
June
August
October
Phytochrome tells plants
•
•
•
•
If they are near the surface
About their plant neighbors
Whether it is time to flower
And lots more