Photoperiodism Flashcards
Flowering
Annual Rhythm
IMPORTANCE of flowering
Flowering at the right time of the year is vital for plants.
1)delicate flowering structure not damaged by harsh enviro.
2)same species flower same time= cross-pollination
3)plant & pollinator synchronised
4) Some plants can take advantage by growing when other plants don’t( = less shading and comp for resources)
Photoperiodism
How plants respond( w respect to flowering) to the relative amount of light. (photoperiod)
IN REALITY plants respond to amount of NIGHT.
3 tyoes of plants
SD= days Short, Night long (winter)
LD= Day long, night short (summer)
DN= Flowering doesn’t depend on lenght of day or night
Short day plants
-require a short day and long night
- produce flowers ONLY if the photoperiod is LESS than a certain critical length.
E.g. short day species with a 10hr critical photoperiod will flower only if the dark period exceeds 14hrs (i.e early spring, autumn or winter).
Long day plants
-require a long day and a short night
- require a photoperiod that exceeds a certain critical length for flowering to take place.
-These plants flower in SUMMER (i.e lettuce, petunia)
Day-neutral plants
- flowering of the plants is relatively unaffected by the period of light per day
- e.g. tomatoes
Other determinants of flowering other than photoperiodism
temperature, moisture, soil nutrients and amount of crowding (competition).
Critical length
amount of daylight required to produce flowers
Photoreceptors
detect amount of light / monitor it
Phytochromes
Photreceptors
What is it?
Plants absorb light via blue light photrecpetors and phytochromes (Pr and Pfr)
Pr and PFr responsible for
Flowering and germinating activiities
Pr and pfr stand for
Pr= Phytored
Pfr= Phyto fara-red
Phytochromes: why
Germ and flowers occur in response to red and fara red light. Effects are reversible for both (conversion of pr to pfr and vice versa).
- Pr and pfr are isomers
- r light activated Pr -> Pfr
-fara r light activstes Pfr->Pr
Diagram:
Pr to Pfr = sun, quickly
Pfr to Pr, moon. slowly
Phytochrome system
- Ability of plants to activate the photoperiod response ( to flower) is meditated by a PIGMENT called PHYTOCHROME.
1) Light detected by phytochrome
2) Phytochrome has 2 diff forms which correspond to the 2 diff wavelengths of light (PR and PFR)
PR - absorbs red light
PFR- absords far red light
3) When PR absorbs light it QUICKLY converted to PFR
When PFR absorbs far red light it is SLOWLY converted to PR.
4) In DARK PFR slowly -> PR
- sunlight has red>far red light so during DAY PR –> PFR.
Levels of PFR determine…..
whether plant flowers or not.
LDPlants = flower in summer = long day, short nights.
- Pfr stimulates flowering at night, Pfr doesn’t all get converted, so some are left as the nights are short.
If day is long….
Pfr levels increase and LDP flower.
- due to higher Pfr levels promote flowering in LDP.
In SDP, high levels of Pfr INHIBITS flowering.
If night is long….
Pfr —> Pr
Pr levels increasing and SDP flower
- SDP flower when Pr levels increase, cause high Pr levels PROMOTES flowering in SDP.
