photoperiodism its discovery,significance,classifications,mechanism,critical day length,quality of light, night break phenomenon,phytochrome.florigen,floering genes, circadian rhythm
photoperiodism its discovery,significance,classifications,mechanism,critical day length,quality of light, night break phenomenon,phytochrome.florigen,floering genes, circadian rhythm
molecular and genetic analysis of floral induction is an integrated approach, taking into consideration various genes involved in the four major pathways of flowering process
intro-hostory and discovery-characteristics of phytochrome-chemical nature of phytochrome-mode of action-mechanism-phytochrome mediated physiological responses-phytochrome is a pigment system:some evidences-role of phytochrome
Self-incompatibility refers to the inability of a plant with functional pollen to set seeds when self pollinated. It is the failure of pollen from a flower to fertilize the same flower or other flowers of the same plant.
This presentation includes, Single-locus self-incompatibility- {Gametophytic self-incompatibility (GSI) and Sporophytic self-incompatibility (SSI)},2-locus gametophytic self-incompatibility, Heteromorphic self-incompatibility,Cryptic self-incompatibility (CSI) and Late-acting self-incompatibility (LSI).
Everything about photoperiodism from scratch to smart, from the oldest models to the latest models as well as proposed one, exclusive and elusive illustrations and models for proper understanding
Lecture 2 from Pat Heslop-Harrison for BS1003 - Cell and Developmental Biology. The transition to flowering. How do plants decide to flower? How do they respond to daylength (photoperiod) and temperature? For information from light, phytochrome is the photoreceptor, but not the clock/time measuring process. Pfr (phytochrome far red) is always the active form of phytochrome, but the function is different in long day plants and short day plants. Pfr promotes flowering in LDPs but inhibits flowering in SDPs.
molecular and genetic analysis of floral induction is an integrated approach, taking into consideration various genes involved in the four major pathways of flowering process
intro-hostory and discovery-characteristics of phytochrome-chemical nature of phytochrome-mode of action-mechanism-phytochrome mediated physiological responses-phytochrome is a pigment system:some evidences-role of phytochrome
Self-incompatibility refers to the inability of a plant with functional pollen to set seeds when self pollinated. It is the failure of pollen from a flower to fertilize the same flower or other flowers of the same plant.
This presentation includes, Single-locus self-incompatibility- {Gametophytic self-incompatibility (GSI) and Sporophytic self-incompatibility (SSI)},2-locus gametophytic self-incompatibility, Heteromorphic self-incompatibility,Cryptic self-incompatibility (CSI) and Late-acting self-incompatibility (LSI).
Everything about photoperiodism from scratch to smart, from the oldest models to the latest models as well as proposed one, exclusive and elusive illustrations and models for proper understanding
Lecture 2 from Pat Heslop-Harrison for BS1003 - Cell and Developmental Biology. The transition to flowering. How do plants decide to flower? How do they respond to daylength (photoperiod) and temperature? For information from light, phytochrome is the photoreceptor, but not the clock/time measuring process. Pfr (phytochrome far red) is always the active form of phytochrome, but the function is different in long day plants and short day plants. Pfr promotes flowering in LDPs but inhibits flowering in SDPs.
Introduction:
Vernalization is the process whereby flowering is promoted by a cold treatment given to a fully hydrated seed or to a growing plant.
Dry seeds do not respond to the cold treatment.
Due to vernalization, the vegetative period of the plant is cut short resulting in an early flowering.
Also called yarovization.
Without the cold treatment, plants that require vernalization show delayed flowering or remain vegetative.
In many cases, these plants grow as rosettes with no elongation of the stem.
History:
Klippart,1857- first noticed the low-temperature requirement for flowering while working with winter wheat and spring wheat.
Lysenko,1938-used the term vernalization for a low-temperature promotion of flowering in plants.
Chourad ,1960- defined vernaliZation as “acquisition or acceleration of the ability to flower by a chilling treatment”.
Vernalization
For vernalization the seeds are allowed to germinate for some time and then are given cold treatment from 0 ̊C to 5 ̊C.
The period of cold treatment, varies from few days to many weeks.
After the cold treatment the seedlings are allowed to dry for some time and then sown.
Vernalization prepares the plant for flowering.
The cold stimulus usually perceived by the apical meristems. But in some species, all dividing cells of roots and leaves may be the potential sites of vernalization eg. Leennario biennis.
Vernalization induces the plant to produce a hormone called vernalin. It was discovered by Melcher(1936).
The vernalization stimulus can be transmitted from one plant to another through grafting.
The age of the plant is an important factor in determining the responsiveness of the plant to the cold stimulus and it differs in different species.
The suitable temperatures for vernalization ranges between 1 to 6 ̊c.
At higher temperature from 7 ̊c onwards response of the plant is decreased.
A temperature of about 12 to 14 ̊c is most ineffective in vernalizing the plant.
The vernalization is an aerobic process and requires metabolic energy.
In the absence of oxygen cold treatment becomes completely inefficient.
A sufficient amount of water is also essential.
Vernalization of dry seeds is not possible.
Factors affecting Vernalization:
Site of vernalization
Age of plants
Appropriate low temperature
Duration of exposure
Mechanism of vernalization:
Two theories..
1. Phasic development theory
2. Hormonal theories.
Epigenetic Changes in Gene Expression:
Vernalization May Involve Epigenetic Changes in Gene Expression.
Changes in gene expression that are stable even after the signal that induced the change (in this case cold) is removed are known as epigenetic regulation.
One model for how vernalization affects flowering is that there are stable changes in the pattern of gene expression in the meristem after cold treatment.
The involvement of epigenetic regulation in the vernalization process has been confirmed in the LDP Arabidopsis.
the flowering process is the combined effect of environmental factors like light and temperature. vernalisation is the epigenetic memory that leads to genetic regulation of the process
Photoperiodism is the phenomenon of physiological changes that occur in plants in
response to relative length of day and night (i.e. photoperiod). The response of the plants to
the photoperiod, expressed in the form of flowering is also called as photoperiodism. The
phenomenon of photoperiodism was first discovered by Garner and Allard (1920).Depending
upon the duration of photoperiod, the plants are classified into three categories.
1. Short day plants (SDP)
2. Long day plants (LDP)
3. Day neutral plants (DNP)
Vernalization is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, but they may require additional seasonal cues or weeks of growth before they will actually flower.The vernalization requirement ensures that plants do not flower in the fall when the environmental conditions are unfavorable for reproduction. The strength of the vernalization requirement can vary within plant species.
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Vernalization
1.
2. UNIVERSITY OF AGRICULTURAL SCIENCES, RAICHUR
COURSE TITLE : Plant developmental Biology,Physiology and
Molecular basis
CPH -502(2+0)
SUBMITTED TO :- Dr. Suma T.C
Assistant professor ,
Department of Crop Physiology
SUBMITTED BY :- Vishal Reddy
Jr. M.sc (Agri).
PG18AGR10062
5. INTRODUCTION
• Vernalization word derived (from Latin vernus, "of the spring")
• Literal meaning of vernalisation is bringing to spring condition.
• For some plants , vernalization is an absolute requirement or in
some cases it simply assists in flowering.
• The duration of low temperature treatment required varies from
four days to three months.
“Vernalization is the induction of a plant's flowering process by
exposure to the prolonged cold of winter, or by an artificial equivalent”.
6. HISTORY
• John Hancock Klippart,1857- first noticed the low temperature
requirement for flowering while working with winter wheat and
spring wheat.
• Lysenko,1938-published his works on the effects of cold on cereal
seeds, and coined the term “Jarovization” (Jarovoe in Russian,
originally meaning fire or the god of spring) later, translated the
term into “Vernalization"
• P.Chouard ,1960- defined vernalization as
“acquisition or acceleration of the ability to flower by a chilling
treatment”.
7. TYPES OF VERNALIZATION
1.FACULTATIVE VERNALIZATION
Flowering will appear earlier once exposed to low temperature.
Eg., Winter annual Triticale (fig 1)
2. OBLIGATE VERNALIZATION
Must expose to low temperature to a desired period of time
Eg., Biennial plants (Cabbage) fig 2
(fig 1) (fig 2)
8. SITE OF VERNALIZATION
• Metabolic active apical meristem is the site of temperature
perception for flower initiation.
• Younger leaves are more susceptible to vernalization.
• The low temperature stimulus is received by the shoot apex
of a mature stem or embryo of the seed.
9. TECHNIQUE OF VERNALIZATION
The seeds are first soaked in water and allowed to germinate in
processing chamber at 10-12˚C temperature
Then seeds are transferred to low temperature (3-5)˚C and
kept for correct period of time.
Seeds are dried and sown in the field in proper oxygen and
water supply condition
(Which varies among different varieties, from few days to 30 days)
10. VERNALIZATION AND AGE OF PLANTS
• In cereals vernalization best occurs in germinating seeds and even at embryonic
stage in mother plant.
In the opinion of Sarkar (1958)
• Hyoscyamus niger gets maximum sensitivity to chilling effect after 30 days of
growth.
• In Oenothera maximum sensitivity to low temperature occurs only when the
plants bear 6-8 leaves
12. Hypothesis of Hormonal involvement
• Proposed by Chailakhyan
• ‘ Vernalin’ is produced in some biennials (winter cereals) and perennials
(Chrysanthemum , apple) at low temperatures.
• In long day plants vernalin is converted into gibberellin (‘Anthesin’ is
present in long day plants).
• ‘Anthesin’ along with ‘vernalin’ cause flowering in long day plants.
• But in short day condition ,the vernalin is not converted to gibberellin
(because they lack anthesin),hence flowering does not occur
13.
14. Hypothesis of Phasic development
•Proposed by Lysenko
•The development of annual seed plant consists of a
series of phases, which occurs in predetermined
sequence, next phase only initiates on the termination of
the previous phase.
There are two phases
1. Thermostage
2. Photostage
15. 1. Thermostage
• It is vegetative phase which requires low temperature
(0 -14˚C) and suitable moisture and aeration.
• This stage is of variable length and depends on the nature
of plants and environment.
2. Photostage
• This phase requires high temperature.
• Here vernalin helps in synthesis of florigen.
Winter wheat complete their life cycle more rapidly
when given a short day and low temperature during
thermostage and a long day and higher temperature in
photostage.
16. VERNALIZATION STIMULUS
• It is received by vernalin ( a postulated chemical )
• Transmission of vernalization stimulus across a graft union in
Hyoscyamus niger has been studied by a German botanist ,
G.Melchers (1939)
• He took two plants/two branches , one previously vernalized and
other unvernalized and grafted them together . Both flowered in
appropriate photoperiod condition , but unvernalized plant alone
failed to flower.
• From above experiment it is obvious that vernalization stimulus is
transmitted from vernalized to unvernalized plant/branch .
17. Experiments to demonstrate that flowering stimulus can translocate from
vernalized plant to unvernalized plant through graft union
18. HORMONAL MECHANISM OF VERNALIZATION
• The genes VIN3, VRN1 and VRN2 act to let the plants know
that enough winter weather has occurred and the hold on
flower development (via FLC and FRI) can be let go.
• The gene FLC functions to keep plants from flowering, while
genes like AP1, SOC1, FT, and LEAFY turn on genes to
promote flower production.
• In perennials and winter annual plants, FRI serves to keep
plants from flowering through the work of FLC until a certain
amount of winter temperatures have passed.
19. (Pointed arrows mean activation or promotion of the next downstream thing, while
blocked lines indicate repression of the next step in the pathway)
20. •VIN3 – Vernalization insensitive 3
•VRN1 - Vernalization 1
•VRN2 – Vernalization 2
•FLC – Flowering Locus C
•FRI – FRIGIDA ( regulates flowering time )
•AP1 – Activator protein 1
•SOC1 – Supressor of Overexpression of CO1
•FT – Flowering locus T
21.
22.
23. 1.Water and Oxygen
• Seed need to imbibe 10-20 % water, dry seed cannot be vernalized.
• Similarly oxygen is also necessary for vernalization. Oxygen is used during
respiration. A germinating seed need energy. This energy is provided by
respiration. The inhibition of respiration blocks the process of vernalization.
2.Temperature
• The seeds are exposed to low temperature during vernalization.
• Temperature lower than 4°C is not effective. Similarly, temperature above 12°C
does not cause vernalization,the duration of vernalization varies in different
species.
3.Devernalization
The exposing of vernalized seed to high temperature (30 -35°C) , lose the effect of
vernalization called as Devernalization.
FACTORS AFFECTING VERNALIZATION
24. 4.Effect of light
• The seed of a plant can be vernalized in the presence or absence of light,
• But many plants like carrot require both vernalization and photoperiodic stimulus.
They must be first vernalized. Then are given photoperiodic stimulus for
flowering.
5.Effect of hormones
Many species like carrot and Hyoscyamus have obligate vernalization requirement.
These plants show rapid flowering after vernalization due to GA synthesis,It causes
both bolting and flowering.
25. PRACTICAL APPLICATIONS
• Due to vernalization the vegetative period of the plant is cut short
resulting in an early flowering.
• Vernalization increases the resistance of plants to fungal diseases.
• It increases the cold resistance of plants.
• In the biennials ,vernalization induces early flowering and early fruit
setting.
• Flowering can be induced by grafting and this feature is used in
horticulture.
• It also helps in crop improvement.
26. Effect of vernalization on seed production of
onion
-Esmat Jahan Ami
• Bulbs of 20 ±1g size of local cultivar Taherpuri were used as
planting material and were vernalized at the duration of 14
days in freezing.
• The experiment consisted two levels of vernalization
1.Vernalization of mother bulbs at 5°c ± 1
2. No Vernalization
• Cold treatment of mother bulbs influenced the plant to
produce maximum number of leaves,maximum seeds per
umbel were produced from the bulbs vernalized at 5°c ± 1.