photo periodicity and vernal is at ion
TRANSCRIPT
Photoperiodicity and Vernalisation
By : Asri IvoDewi Sahfitri Tanjung
Dwi RahmanarsihShofia LubisSiti Indriani
Concept of the biological clock1. Endogenous circadian rhythms2. photoperiodism
Biological clock
A roughly 24-hour cycle in the biochemical, physiological, or behavioral processes of living entities on Earth
Occur within the cell
Endogenous circadian rhythms
Many plant activities seem to occur on a daily schedule - some plants open their leaves at dawn and shut them at dusk - some plants may open and shut flowers as the day changes from dawn to dusk
Photosynthesis, auxin production, and the rate of cell division all have regular daily rhythms and these rhythms continue even when environmental conditions are kept constant
Controlled by independent time measuring system (biological clock)
Circadian Rhythms
Entrainment occurs when a periodic repetition of light and dark (or some other external cycle) causes a biological clock to remain synchronized with the same cycle as the entraining factor
Light-dark cycles, light intensity and temperature cycles are the principle sources of entrainment
The main advantage of a biological clock is that it allows the plant to respond to the changes in seasons by accurately measuring changing day length - thus changes in the environment trigger responses that result in adjustments of growth, reproduction, and other activities of the organism
More Circadian Rhythms
PHOTOPERIODISM The biological measurement of the relative lengths of day and night
Garner and Allard (1920’s)
The discovery of photoperiodism
Soybeans (Glycine max) planted over a three-month period all flowered about the same time
Photoperiodism the response by an organism to synchronise its body with changes in day length
At high latitudes this is important because the change in length of the day indicates the season
Days getting shorter indicate winter is approaching
Days getting longer indicate summer is approaching
Some plants regulate their flowering this way
Photoperiodism
Photoperiodism: Types of Plants
3 different types of plants:
◦ “Short Day” flower when days are short, nights are long (Ex. poinsettias, chrysanthemums)
◦ “Long Day” flower when days are long and nights are short (Ex. Spinach, Radish)
◦ “Day Neutral” flowering does not depend on length of day or night (Ex. tomato)
Response varies according to the age of the plant and varies in its intensity
Broadly they can be grouped into three categories
Response to day length
Response to day length
CucumberHollyMaize
Do not respond to day length
DAY-NEUTRAL PLANTS
Chrysanthemum < 15hTobacco < 14h
< 10-16 hSHORT-DAY PLANTS(“LONG-NIGHT”
PLANTS)
Red clover > 9hOats > 12hWinter wheat > 12h
>9-16 hLONG-DAY PLANTS
EXAMPLESDAY LENGTHRESPONSE
Response to day length
Some plants flower only after a CRITICAL DAY LENGTH
Some plants only flower after a CRITICAL NIGHT LENGTH
Chrysanthemum
Critical daylength
CriticalDaylength
(CD)
Xanthium: a short day plant, flowers when CD is LESS than 15.5 hours.
Hyoscyamus: a long day plant, flowers when CD is MORE than 11 hours.
PHOTOPERIODISM K. Hamner (U of Cal.) and J. Bonner (CIT) 1938
PHOTOPERIODISM REDEFINED
K. Hamner (U of Cal.) and J. Bonner (CIT) 1938:◦ Short Day Plants
uninterrupted darkness must be of a certain duration.
(so much darkness or more)
◦ Long Day Plants uninterrupted darkness must be less than a certain
maximum value. (so much darkness or less)
◦ Day Neutral Plants Flowers at a certain level of maturity or in response
to some environmental factor other than the photoperiod.
The control of flowering
Flowering
“Florigen” hormone
Flower buds
Photoperiod mechanism in the leaves
Change in day length
• the flowering signal is generated in the leaf
• the signal goes one way: from the leaf to the apex
• Grafting transmittable
The flowering signal: florigen
?
vegetative or reproductive growth?
SAM
Florigen
Florigen
Florigen
Exp. 1: The leaf or apex of Perilla (a short day plant) was exposed to different daylength.
Exp. 2: Grafting experiment with Perilla
Do plants really measure the length of the daylength?
• Xanthium flowers when the dark period exceeds 8.5 hours.
Hamner and Bonner (1938): Xanthium strumarium, a SD plant with CD = 15.5 hours
• Short interruption of dark period, even by a pulse of light as short as 1 minute delays flowering.
• The relative length of dark is not the determining factor.
Long and Short Day Plants May Flower at the Same time
For plants with a critical night length, a short flash of light in the middle of the night would make the plant behave as if it had been exposed to a long day
The night break phenomenon
The quality of the light
The wavelength of the light used is important
StimulatesInhibits670 – 680nmRed light
ReversesStimulates>700nmFar red light
LONG-DAYSHORT-DAYWavelengthColour
This indicated that there should be a pigment that absorbs red light (in other words this pigment should be blue-green)
This pigment is the mechanism capable of recognising changes in day length
PHYTOCHROME
The pigment
PHOTOPERIODISM H. A. Borthwick and S. B. Hendricks 1950’s
US Ag
Phytochrome exists in two versions which are inter-convertible
PR that absorbs red light PFR that absorbs far red light
The photoperiod mechanism
PR
RED LIGHT
FAR RED LIGHT
PFR
In the short-day plant
PFRPR builds up
Darkness (slow)Far red light (fast)
Short-day plants
FLORIGENActivated
FLOWERING
In the long-day plant
PFR builds up PR
SunlightRed light
Long-day plants
FLOWERING
FLORIGENActivated
Summary
SunlightRed light
Darkness (slow)Far red light (fast)
PFR builds up
Long-day plants
FLOWERING
FLORIGENActivated
PR builds up
Short-day plants
FLORIGENActivated
FLOWERING
VERNALISATION from Latin: vernus, of the spring
Discovered by Trofim Denisovich Lysenko (1898-1976)
Cold/low temperature perceived by the shoot apex. Two phenomena : the growth and the development
Merely prepares the plants for flowering
Overview
Plants differ in age at which they become sensitive to vernalization. E.g. winter annuals(winter rye) respond tolow temperature early in their life cycle (can be vernalized before germination, imbibedseeds)
Vernalization results in competence to flower at the shoot apical meristem
Imbibed Rye seeds exposed to 5ºC for different lengths of time, then immediately treated for 3 d at 35º
Most biennials (grow as rosette during first season and flower in following summer; parsley, carrot) must reach minimal size before they become sensitive.
Effective temperature of vernalisation: 0-10ºC;Effect of cold increases with duration of cold treatment, requiring several weeks of exposure (varies with species) .Vernalization can be lost after exposure to high temperature (devernalization); the longer the exposure to low temp., the more permanent the vernalization effect.
.
Thermostage • First stage and referred to as Lysenko
stage.• Condition for successful passage
* temperature* moisture* aeration* time
Theory
Photostage Photoperiodisme Pronounced effect of the relative length of day and night on the production of flowers.
Third stage Necessary for seed formation
.
The seeds are allow the germinate
Given cold treatments (0-5⁰)Sown
Process
Low temperature Themoinduced condition
Venralin Florigen (The flowering signal)
Mechanism
No vernalization Vernalization
.Vernalization induces flowering in winter annual ecotypes of Arabidopsis thaliana
Plants are genetically identical.
Exposed as a seedlingto 4ºC for 40 days.
Winter annuals require vernalization to flower while rapid-cyclers do not require vernalization.
Arabidopsis accessions have adopted different reproductive strategies
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