Lecture 6 Flashcards
Plants weigh up internal and external signals to decide whether to flower or not. One signal is daylength which plants can measure and this controls photoperiodic flowering. Plants use genes , light signals, circadian clock to control their flowering.
true or false; many plants flower at a precise time of the year
true
when do cherry blossoms and daffodils bloom
spring
when do pohutukawas bloom
early summer
Why is correct flowering time important for a plant
to ensure that seed production is completed successfully
- important for people (harvest; high yield)
- ensure successful reproduction
define photoperiodism
ability to sense and respond to daylength
true or false; photoperiod can control flowering
true
Who coined the term photoperiodism and when
Garner and Allard
1920
What are the 3 main classes of plants
short day plants
long day plants
day neutral plants
What does it mean by short day plant
(8h light/16hr dark)
flowering in response to short days and long nights
give 3 examples of short day plants
poinsettias
rice
soybean
What does it mean by long day plant
(16hr light/8 hr dark)
flowering in response to long days and short nights
give 3 examples of long day plants
Arabidopsis spinach
wheat
lettuce
What does it mean by day-neutral plant
flowering is not controlled by photoperiodism
give 4 examples of day-neutral plants
tomato
cucumber
sunflower
maize
what type of plant is morning glory
short day
what type of plant is arabidopsis
long day
What does the GI (GIGANTEA) gene promote in Arabidospsis plants
promotes flowering
- mutation in the gene can inhibit flowering
What does it mean by Circadian rhythm
occur every 24 hrs
- 24 hr cycle
- continues even in absence of exogenous cues
What did De Marian propose about the movement of plants and when
1727
rhythms in leaf movement in the absence of daily cues
What did Darwin propose about plant movement and when
1898
published the power of movement in plants
Give 5 examples of activities that are controlled by the circadian clock
- occur once every 24 hrs
- leaf closure
- flower opening and closing
- stomatal opening and closing
- Most biochemical and physiological processes
eg. Carbon fixation, nitrate reductase, growth - gene expression rhythms ~ 30% Arabidopsis genes
What is the function of the circadian clock
allows plants to get ready ahead of time
eg. photosynthesis (onset earlier) occurs in day time only
- most growth expansion of leaves occur at night (use their energy acquired during the day at night)
- seasonal behavior (eg. photoperiodic flowering)
What are the three experiments to test out control in flowering
- ) Night break experiment (short day plants)
- ) different red light quality flashed on the plant (long day plants)
- ) grafting
Describe the night break experiment
- flash or light during the night
- even a small interruption of light can ruin the perception for flowering
- have indicated that night length is important
(length of dark period a critical parameter particularly for short day plants)
Describe the experiment where far red light and red light were flashed at long day plants
- flash of red light interferes with the flowering of chrysanthemums
- far red light cancel the effect of red light
- applies for both short and long day plants
- phytochrome is the receptor perceiving the night break
Describe the experiment of grafting
floral induction by day length is graft-transmissible
- mobile plant flowering hormone florigen is graft transmissible (by splicing two plants together)
- FT gene
what are the commercial applications of controlling flowering of a plant
inducible flowering to specific dates of the year, such as Christmas, Valentines day
Describe how poinsettias have been manipulated for commercial use
short day plants
need 14 hr dark
usually flower Feb/Mar(US)
Aug/Sep( NZ)
When are poinsettias induced to flower in USA
at Xmas
by 14 hr dark treatments (Nov)
when are poinsettias induced to flower in NZ
delayed from flowering until xmas by light flashes during the night
What are other benefits of delaying flowering time
increase vegetative yield
- biofuel, forage, wood
What are crops customized to
- to different geographical regions and climates
eg. heat resistance
What is florigen and where is it produced
produced in the leaves in inductive day lengths and transported to the shoot apex to convert meristems from vegetative to floral
