Photoperiodism

Question 1

Flowering

Answer 1

Annual Rhythm

Question 2

IMPORTANCE of flowering

Answer 2

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)

Question 3

Photoperiodism

Answer 3

How plants respond( w respect to flowering) to the relative amount of light. (photoperiod)
IN REALITY plants respond to amount of NIGHT.

Question 4

3 tyoes of plants

Answer 4

SD= days Short, Night long (winter)
LD= Day long, night short (summer)
DN= Flowering doesn’t depend on lenght of day or night

Question 5

Short day plants

Answer 5

-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).

Question 6

Long day plants

Answer 6

-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)

Question 7

Day-neutral plants

Answer 7

• flowering of the plants is relatively unaffected by the period of light per day
• e.g. tomatoes

Question 8

Other determinants of flowering other than photoperiodism

Answer 8

temperature, moisture, soil nutrients and amount of crowding (competition).

Question 9

Critical length

Answer 9

amount of daylight required to produce flowers

Question 10

Photoreceptors

Answer 10

detect amount of light / monitor it

Question 11

Phytochromes

Answer 11

Photreceptors

Question 12

What is it?

Answer 12

Plants absorb light via blue light photrecpetors and phytochromes (Pr and Pfr)

Question 13

Pr and PFr responsible for

Answer 13

Flowering and germinating activiities

Question 14

Pr and pfr stand for

Answer 14

Pr= Phytored
Pfr= Phyto fara-red

Question 15

Phytochromes: why

Answer 15

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

Question 16

Phytochrome system

Answer 16

• 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.

Question 17

Levels of PFR determine…..

Answer 17

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.

Question 18

If day is long….

Answer 18

Pfr levels increase and LDP flower.
- due to higher Pfr levels promote flowering in LDP.

In SDP, high levels of Pfr INHIBITS flowering.

Question 19

If night is long….

Answer 19

Pfr —> Pr
Pr levels increasing and SDP flower
- SDP flower when Pr levels increase, cause high Pr levels PROMOTES flowering in SDP.