Photoperiodism is the response of plants to changes in day length and allows plants to synchronize their growth and flowering with the seasons. It is regulated by the phytochrome pigment, which exists in two interconverting forms (Pr and Pfr) that are sensitive to red and far red light. In long day plants, the Pfr form predominates during long days and induces flowering, while in short day plants the Pr form builds up during short days and induces flowering. This ensures that plants flower at the appropriate time of year to maximize reproductive success.

1. PHOTOPERIODISM
The biological measurement of the relative lengths of day and night
Dr. Tushar Wankhede, MSc, Ph.D.(SET)
Associate Professor in Botany
Shri Shivaji Science College, Amravati
NAAC Reaccredited “A” with CGPA 3.13
College with Potential for Excellence (CPE)

3. Photoperiodism
 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 (July to December)
 Days getting longer indicate summer is
approaching (January to June)
 Plants regulate their flowering this way

4. Can you imagine ??
Flowers can tell you time

5. Earth rotation and Seasons

8. Photoperiodism ????
Does Any Significance ???? Or just fantasy

9. Neelakurinji (Strobilanthes kunthianus) is a shrub that is found in
the shola forests of the Western Ghats in South India. Nilgiri Hills, which literally
means the blue mountains, got their name from the purplish blue flowers of
Neelakurinji that blossoms only once in 12 years.
Of all long interval bloomers Strobilanthes kunthianus is the most rigorously
demonstrated, with documented bloomings in 1838, 1850, 1862, 1874, 1886, 1898, 1910,
1922, 1934, 1946, 1958, 1970, 1982, 1994, 2006 and 2018.

10. Leaf angle
Leafangle
Leaf angle
already
starts to
change
before the
light of day.
Leaf angle
changes
continue
their rhythm
also in
continuous
dark.
Example of a circadian rhythm:
The circadian oscillator controls the leaf movement rhythm in beans

11. Photoperiodism and flowering
Effect of day length on flowering
and other activities (seed
germination, seed dormancy,
bud break, bud dormancy) in
temperate regions of the
northern hemisphere.

12. Circadian rhythms allow to monitor (to
visualize) the biological (circadian) clock
Without light detection (mediated by Phy and Cry receptors) the
period of the biological clock becomes slightly longer than 24
hrs. The 24 hr cycle of light detection allows to entrain the clock
to maintain a 24 hr cycle.

15. State of an Art : History

16. State of an Art : Classification

18. 12
Hrs.
Night
12
Hrs.
Day
Critical
length
LDP SDP
DLP
Cajlachjan (1938) proposed hypothetical flowering hormone
concept of Florigen
Flower Bud flower Bud flower Bud
flower flower flower
24
Hrs.
Perio
d

19. LDP SDP DNP
Long Day Plant Short Day Plant Day Neutral Plants
Flowering is induced under
Long Day Length conditions
Flowering is induces under
Short Day Length
condition
Flowering is not depend
upon Day Length
conditions
Long Day length Short Day length Independent of light
Short Night Length or Short
Night Plants
Long Night Length or
Long Night Plants
Throughout the year
Summer Variety’s Winter Variety’s All time available
Eg. Spinach, Wheat, Raddish ,
Beet, lettuse
Eg. Cosmos, Dahlia
Chrysenthemum,
Marigold
Eg. Tomato, Cucumber,
Sunflower

20. State of an Art : Classification

21. The control of flowering
Flowering
“Florigen” hormone
Flower buds
Photoperiod mechanism
in the leaves
Change in day length

22. The night break phenomenon
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

23. The pigment
 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

24. The photoperiod mechanism
 Phytochrome exists in two versions which
are inter-convertible
 PR that absorbs red light
 PFR that absorbs far red light
PR
RED
LIGHT
FAR RED
LIGHT
PFR

25. In the short-day plant
PFR PR builds up
Darkness (slow)
Far red light (fast)
Short-day
plants
FLORIGEN
Activated
FLOWERING

26. In the long-day plant
PFR builds up PR
Sunlight
Red light
Long-day
plants
FLOWERING
FLORIGEN
Activated

27. Summary
Sunlight
Red light
Darkness (slow)
Far red light (fast)
PFR builds up
Long-day
plants
FLOWERING
FLORIGEN
Activated
PR builds up
Short-day
plants
FLORIGEN
Activated
FLOWERING

28. Significance of photoperiodism
 Photoperiodism is an example for physiological
preconditioning.
 The stimulus is given at one time and the response
is observed after months. Exposure to longer
photoperiods hastens flowering
(E.g). In wheat, the earing is hastened.
 During long light exposure, Pr form is converted
into Pfr form and flowering is initiated. If dark period
is greater, Pfr is converted into Pr form that inhibits
flowering.
Very Important

29. Significance of photoperiodism
The important phytochrome mediated photo responses in plants include
 photoperiodism and seed germination
 gamete expression
 bud dormancy
 rhizome formation
 leaf abscission
 epinasty
 flower induction
 protein synthesis
 pigment synthesis eg. chlorophyll n anthocyanin (Algae)
 respiration and stomatal differentiation
 In lower plants….protonema, spores n rhizoids
formation
Very Important

31.  In 1952, H.A. Borthwick and H.B. Hendricks from Department
of Agriculture, Beltsville Maryland, United States detected light
effects on flowering.
 Phytochrome is a photoreceptor molecule which mediates
several developmental and morphogenic responses of plants to
light.
 This pigment consist of inactive [Red form-Pr] and active Far
Red [Pfr] form which triggers responses.
 The effect of red or far red light were reversible and very fast
involving single photo-transforming pigment

33.  isolation of phytochrome was done by W.L. Butler and his
colleagues [1959-64] from USDA, Beltsville.
 Phytochrome is a protein can be isolated from seedling by using
column, ion exchange and gel exclusion chromatography.
 The pigment can be precipitated from the extract by ammonium
sulphate.
 Affinity chromatography of phytochrome using agarose
immobilized Cibacron Blue F3 also used to purify phytochrome.
 The quantity of phytochrome can be can be detrmined by
specctrophotometer, Immunochemical and radio-immuno assay
methods.
 Phytochrome can be isolated from variety of sources
 Oats, Tobbaco, Maize
 Rye, Pea, lettuce
 In Algae…..Mestaenium
 In Bryophytes….Sphaerocarpus

34.  Distribution
At various locations
 Roots
 Stems
 Hypocotyl
 Cotyledons
 Coleoptiles
 Leaf Blades
 Petioles
 Vegetative buds
 Developing fruits
 Floral receptacles
 Inflorescences
 In cellullar distribution
 Etioplast
 Chloroplasts membrane and plasmalemma

35. Physico-chemical nature
 Two types have been identified.
 Small: Molecular weight = 60 kDa and believed to be
degradation product of large phytochrome not appeared in vivo.
 Large: is a natural phytochrome. It’s a Dimer with a mol. Wt.
of each monomer as 120 kDA.
 Proteolytic activity degrades it during extraction and
degradation.
 Phytochrome is a conjugated protein
as it contain a visible chromophore and
appears as bluish.
 The molecule is a dimer with two
chromophore and two globular protein.
There are disulphide bonds [S-S] bonds
per monomer not involved in holding
subunits together. Two monomeric
units are identicle and each with 1100
amino acids in sequence.

36.  Secondary structure composed of half of the protein with equal
amount of alpha- helix and beta structure while remainder is
aperiodic.
 In Aradopsis five types namely
1. PHY A : is light labile & accumulates in dark. High in
etiolated seedling. Gives high irradiance responses.
2.
3. PHY B : is light Stable. Involved in germination response.
4. Elongated coleoptiles, stems, petioles and root hairs.
5. Also showed shade avoidance response.
6. PHY C, PHY D and PHY E : General photo-responce and
depends upon concentrations.
All these pigments are recognized as a product of five genes.

38.  Chromophore: Exact
number of chromophore
molecule is not known
But ,
 There is one chromophore
per monomeric unit & its
structure is simillar to the
algal pigment 6-Phycocyanin.
 Binding the chromophore
to the protein involved a thio-
easter linkage through
cysteine to the C-2 side chain
of ring A.
 B ring is also involved in
binding the protein thr its
side chain [CH2]2 COOH.
When phytochrome undergo Pr Pfr
interconversions the configuration of
unit A changes.
Phytochrome also contain one
phosphate per monomer but its
function was unknown.

39. Function Pr PFr
1. Activity Is a Inactive form Is a Active form
2.Absorptivity 660 nm less absorption 730nm less absorption
3. Sequestering Pr is diffusing in cytosol Pfr associated in discret
areas
4.Pelletability Supernatent of plant
extract
Present in pellets
5. Reactivity Non active than Pfr Active towards urea, metal
ions, Cu, Co2, Zn, and
methyl meleimide

40.  Phytochrome mediated responses
 Seed germination
 Seedling growth
 Flowering
 Flavonoids biosynthesis
 High irradiance responses
 Physiological and biochemical responses

44. G-Protein Cascade
G proteins, also known as guanine
nucleotide-binding proteins, are a family
of proteins that act as molecular switches inside
cells.

49.  Cold-treatment
 In many species temperature has a profound effect on flowering.
 Definition: The acquisition or acceleration ability to flower by a
chilling treatment is termed as Vernalization.
 Latin word Vernal = Spring like
 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.
 Russian scientist T.D. Lysenko [famous for Lysenko Genetics]
demonstrated that the winter variety of wheat, rye, and barley
could be planted in the spring to yield at the same time, the
summer varieties did if treated with cold.
 Biennial plants shows Vernalization which requires winter
season before flowering.

50.  Many plants grown in temperate climates require vernalization
and must experience a period of low winter temperature to initiate
or accelerate the flowering process.
 This ensures that reproductive development and seed
production occurs in spring and summer, rather than in autumn.
The needed cold is often expressed in chill hours.
 Typical vernalization temperatures are between 2 - 5 or 10
degrees Celsius (40 and 50 degrees Fahrenheit)
 For many perennial plants, such as fruit tree species, a period of
cold is needed first to induce dormancy and then later, after the
requisite period of time, re-emerge from that dormancy prior to
flowering.
 Many monocarpic annuals and biennials, including some
ecotypes of Arabidopsis thaliana and winter cereals such as wheat,
must go through a prolonged period of cold before flowering
occurs.

51.  After a prolonged treatment at cold temperature receives proper
photoperiod treatment and flowering induces.
 Plant species like
 Secale cereale
 Aradpsis thaliana
 Rye
 Plant Hyoscyamus niger must be 10 days old and in Rossette
state before it can be vernalized.

52.  Site of Vernalization
 In seedling and in mature plants
 Shoot apex or shoot tips receives
vernalization response.
 Plants like Chrysanthemum, sugar-
beet and celery the grafting
experiment showed the stimulus
translocation to other parts of the
plants.
 Once the stimulus is vernalized, the
stimulus is transmitted to all other
tissues to develop vernalized state.
 But, in plant Lunaria biennis found
younger leaves are capable of being
vernalized while older leaves ceases
the growth or do not respond.

56.  Physiology and Biochemical changes during vernalization
 Freezing is not essential to bring out changes
 Physical processes involved rather than Physiological.
 Cold treatment to rye found ineffective in the anaerobic
conditions.
 In cultured plants supply of sugars is needed for vernalization.
 It also suggested that the compound formed at vernalysed tips
induces florigen or action of florigen.
 This chemical demonstrated in Grafting experiment.
 I. Melcher and A. Lang suggested that the stimulus is
transmitted by Chilling and called it as vernalin.

57.  This stimulus is not as same as florigen as non-inductive to
photoperiods.
 This may be unusual phenomenon. But formation of vernalin is
unusual process.
 Devernalization:
It is possible to devernalize a plant by exposure to high
temperatures subsequent to vernalization. For example,
commercial onion growers store seeds at low temperatures, but
devernalize them before planting, because they want the plant's
energy to go into enlarging its bulb (underground stem), not
making flowers

58. Effect of water and oxygen:
By just treating the seedling with cold temperature,
the said structures do not get verbalized. Along with
the cold treatment plants also require water and
oxygen for effective vernalization.
The seeds or embryos should possess at least 40-50%
water in their cells, without which cold treatment has
no effect. Similarly oxygen is very essential; probably
it is required for biological oxidation.
The essentiality of carbohydrates for effective
vernalization supports the view of requirement of
oxygen. Still, it is difficult to explain how cells use
carbohydrates and oxygen for enzymatic oxidative
process at such low temperature.

60. Spring…….bringing back the life

61. TROPISM
THE TYPES OF MOVEMENT
OBSERVED
IN PLANTS

62. Plants shows some kind of reorientation in their organs in response
to certain external stimuli such as light, gravity and water.
This orientation generally also termed as plant movement.
These are
1. Growth movement : The changes in the plant due to external
stimulus is plastic or irreversible and happened due to the growth
in the plant part.
2. Reversible movement : No growth but changes is elastic
Depending upon the direction of the plant to the stimulus there are
two responses
A] Tropic response: Related to direction of the stimulus i.e. Same
[positive] or or opposite [Negative]
B] Nastic response: Unrelated to the direction of stimulus.

63. Tropism
is a biological phenomenon,
(from Greek τρόπος, tropos, "a turning")
indicating growth or turning movement of a
biological organism usually a plant, in
response to an environmental stimulus.

65. Vital movements : Exhibied ONLY by living cells or organisms.
Movement of locomotion : Whole plant body or cell , part movable
Autonomic or spontaneous movement : In response to stimulus
A] Ciliary movements : Movements by
flagella or cilia as in Volvox or Chlamydomonas
B] Amoeboid : Movement by pseudopodium
In Myxomycetes fungus like amoeba.
C] Cyclosis : Cell organs move around
in cytoplasm . Algal cells like Chara.

66. Vital movements : Exhibied ONLY by living cells or organisms.
Movement of locomotion : Whole plant body or cell , part movable
Paratonic or induced movement : In response to external stimulus
D] Phototactic movements : In response to
Light . Ex zoospores in Volvox
E] Chemotactic : Response to external chemical
Stimulus as in bryo - pteridophytes , antherozoid attract
towards adour of archegonial secretions
F] Thermotactic : response to external heat
Stimulus Ex. Chlamydomons cells placed on
slide and heated at one corner it will go towards
warmer side positively. Viceversa if more heated.

67. Vital movements : Exhibied ONLY by living cells or organisms.
Movement of curvature : Plant body fixed but movement is
restricted to bending or curvatur to some of their parts only.
Autonomic movement: In response to stimulus
Growth movements
I] Nutational
Euphorbia plants
G] Hyponastic movement
Telegraph plant
H] Epinastic / Hyponastic
Fern Plants

68. A directional growth movement made by a part of a
stationary plant response to unilateral stimulus. The
dictionary defines tropism as an orientation of an organism
to an external stimuli.
There are numerous types of tropisms :
• Hydrotropism
• Phototropism
• Geotropism
• Chemotropism
• Thigmotropism
• Heliotropism
• Thermotropism
• And many more………..
(These are the 3 main
types of tropism and
these would broadly
discussed accordingly.)

69. Stimulus
Tropism
Response
WaterGravity Unilateral light
Shoot
Root
Hydrotropism
No response
Positive
Geotropism
Negative
Positive
Phototropism
Positive
Negative

70. GEOTROPISM
Geotropism is the growth of a living organism in response to
gravity.
There are two types of geotropisms. They are:
1. Positive geotropism
2. Negative geotropismPositive Geotropism
It is the growth of an organism
(i.e. plants) towards the centre
of the earth.
Negative Geotropism
It is the growth of an
organism away from the
centre of the earth.
An example of geotropism is
given in the picture.
Positive
Geotropism
Negative
Geotropism

71. IMPORTANCE OF
GEOTROPISM
Provides firm anchorage for roots.
Ensure the plant can get adequate
supply of water & mineral salts.

74. GEOTROPISM

77. PHOTOTROPISM
The growth response of a living organism
on response to light direction is called
phototropism. Like geotropism even
phototropism is of 2 types: 1. Positive
2. Negative
In positive phototropism living
organism grow towards the light.
For example- Stems are
positively phototrophic.
In negative phototropism living
organisms grow away from the light. For
example- Roots are negatively
phototrophic.
Positive
Phototropism
Negative
Phototropis
m

78. IMPORTANCE OF
PHOTOTROPISM
Photoreceptors: phytochromes that sense red
light[11] and cryptochromes that sense blue light
Blue light 440-480 nm.
Two types of pigments : β-carotene, Riboflavin
Located in coleoptile tip, grasses,hypocotyl
seedlings in dicotyledons.
Pigment concentration 10-9 M
 growth pattern different for two sides of
shoot. NEXT

79. IMPORTANCE OF
PHOTOTROPISM
Phototropism enables leaves to be in a
position to receive as much sunlight as
possible for photosynthesis.
NEXT

80. MODE OF PHOTOTROPISM
NEXT

81. HYDROTROPISM
Hydrotropism is the growth of a living
organism in response to water.
Hydrotropism is the directed growth of
the root in relation to the gradient in
moisture. It begins in the root cap with
the sensing of moisture.
Both positive and negative
hydrotropism exist in living
organisms and its direction of
growth depends upon a
stimulus or gradient in water
concentration.
NEXT
Growing towards water
(Positive Hydrotropism)
Growing away from water
(Negative Hydrotropism)

82. IMPORTANCE OF
HYDROTROPISM
Ensures that a plant gets enough
water as a raw material for
photosynthesis & enough mineral
salts to maintain normal growth
NEXT

83. IMPORTANCE OF HYDROTROPISM
NEXT

84. Clinostat
¥Used for controlling experiments
¥Contains a cork disc which can be set to
rotate in a vertical or horizontal plane by
a motor
¥Used to make factors uniform (evenly
distributed).

85. unilateral
light
unilateral
light
in complete darkness
A B C
light-proof
box clinostat
What has happened to the shoots of plants A, B and C ?
Ans: The shoots in pot A respond by growing towards the
light source. The shoot in pot B do not show any curvature
but grow vertically upwards the shoots in pot C grow
vertically upwards with slender and longer nodes, and
carries smaller leaves which are yellow in colour.

86. SOME OTHER
TYPES OF
TROPISM
NEXT

87. THIGMOTROPISM
Thigmotropism is the growth of a living
organism in response to a touch/contact. As
in all tropisms there exist positive and
negative thigmotropism.
Positive thigmotropism is
where a living organism grows
and clings to a wall or a fence.
Negative thigmotropism is the
opposite. It is where a living
organism grows away from a
touching object.
NEXT

88. HELIOTROPISM
Heliotropism is quite similar to phototropism. Now, as we know
that phototropism is the response of a living organism in response
to light but heliotropism is the diurnal motion of the plant flowers
or leaves in response to the direction of the sun. The most famous
examples of heliotropism is the sunflower. Heliotropism was first
described by Leonardo Da Vinci.
NEXT

89. THERMOTROPISM
Thermotropism is the tendency of plants or other
organisms to bend toward or away from heat. s the
movement of a plant or plant part in response to changes in
temperature. A common example is the curling of
Rhododendron leaves in response to cold temperatures.
Thermotropism is often called
thermotropic movement .
NEXT

90. Chemotropism is movement caused by chemical
stimulus in organisms such as bacteria and plants.
An example of chemotropic movement can be seen
during the growth of the pollen tube. This growth
of the pollen tube is always towards the ovules.
Chemotropism
NEXT

91. NASTIC MOVEMENTS

92. NASTIC MOVEMENTS
Tropisms are often slow responses because they result from
differential growth. Depends upon direction.
Nastic movements can be very quick because they are the result of
osmotic changes caused by movements of ions at a cellular level.
Independent upon direction

93. Epinasty : Bending of plant organs towards or more growth on
its upper side is called Epinasty
Ex: Petioles get bend down so that leaves assumes a position by
pointing the tips towards ground.
Unholding of flowers is also epinasty
Unrolling of ferns fronds is epinastic movement

94. Hyponasty is the bending of plant organs upwards due to more
growth on the lower side of the organ.
This may induce by many stimuli.
Ex: Stimulus by light called Photonasty which can be shown in many
plants that in night leaves lamina get curved and and becomes
horizantal in light.
The plant harmone is suppoesd to be invove in curling of leaves.

95. Thermonasty : Growth responses to the changes in temperature are called
thermonasty.
Ex: Such conditions occurs in Tulips flowers showing repeatedly opening and
closing of flowers to temperature changes.
 Very sensitive response even the temperature changes in fraction of degree.
 These changes are permanent growth movements .
 Temperature causes increase in growth of upper side perianth surface to open
flower
 While decrease in temperature results cooling and increases lower surface to
close the flower.
 Under natural condition flowers open at day ans closed at night.

96. Nyctinasty : These are rhythmic procecces controlled by the
time kepping mechanism of th plant i.e. biological clocks.
Ex; In many leguminous plants like Albizzia jullibissin the
leaves are spread over in morning and wwhile fold at evening.
This movement caused by relative changes in cell size on
oppositite sides of the base of the leaflet in shoot zone called
Pulvinous

97. Nyctinasty : Mechanism
Changes found associated are
1. Amount of plant harmone auxin
2. Transfer of K+
3. Water
During daytime large amount of auxins are produced
which transfer to lower side of petiole . this causes
preferential accumulation of K+ in high auxin area
and water get translocate there to rising of leaves.
During night time the auxin transport to the Pulvinous
is reduced and reverse reaction takes place.
In experiments, auxins added to the upper or lower side
of pulvinous causes rising and falling of the leaf.

99. Seismonasty : [Thigmonasty]
Responce to touch , to blow or shaking is known as Seismonasty
Ex; Mimosa pudica is the best example.
It responds to touch by folding their leaflet and their leaves.

101. Seismonasty : Mechanism
In the leaflet, the upper side shrinks so that leaflet close upwards.
In the petiole, the lower side shrinks so that whole leaf drops.
The response are very fast i.e. the leaflet closing may start within 0.1 seconds and
may complete withion a few seconds
Rate of stimulus upto 40-50 cm per second.
Sir J.C. Bose 1914-25 proposed that the stimulus may be means of nervous sysyem
Houvink 1930 found some electric impulse.
sBarbara and Pickard 1976 found transfer of stimuli by several factors like heat,
cold, injury.
1. Stimulus may causes change in permeability of cells rapidly.
2. Presence of large vacuoles
3. sPulvinous action of dehydration and hydration depends upon protein.

102. Molecular mechanism
The swollen base of leaf is called pulvinous.
Two types of cells present in Pulvinous which responds to turgor
pressure.
Flexor and Extensor cells : these are arranged above and below the
central vascular systems.
During folding of leaflet, flexor cells swells and extensor cells shrinks
to bend the pulvinous to fold leaflet.
During straitening of the leaflet the flexor cells shrinks and extensor
cells swell.

103. Seismonasty : Mechanism
The swelling or shrinking of pulvinous cells [Flexor or extensor] is
driven by K+
Pulvinor cells lose k_ ion when shrinking and takes up this ion
actively when swelling.
Most of the K+ ions moves from flexor side to extensor side and back
again during complete cycle of leaf folding and unfolding.
K+ movement is relatively unknown.
Kim H.M. 1995 thought that Ca++ released by inositol triphosphate
triggers from the guard cells.
This cause loss of turgor and consequently the shrinking of the cells.
During folding of the leaves this process takes place in flexor cells and
thus causing the leaves to to bend inwards

105. Seismonasty : Mechanism
Each pulvinous with large thin walled parenchymatous cells called
MOTOR CELLS. Which undergo reversible changes in turgour in
response to stimulus.
When stimulus reaches to pulvinous its osmotic pressure decreases and
water releases from intercellular spaces and suddenly collapse to
drooping down of leaflet and leaf.
Electric pulses through phloem sieve tubes of velocity 2 cm S-1.
Movement of K= from motor cells to apoplast and flaccidity by loss of
turgour and vice versa to restore.
A chemical substance turgorin identified as B-D glucosides of gallic
acid by Herman Schildknetcht in 1984.
Compared with neurotransmitter acetocholine in animals.