The document discusses photoperiodism, the response of plants to changes in day length, which is crucial for flowering. It classifies plants into short day, long day, and day neutral categories based on their light requirements for flowering. The document also touches on floral induction, the genes regulating floral development, and the possible existence of a flowering hormone.

1. The Flowering Process
Presented by: Prajapati Dimple B.
M.sc sem - 3
Botany
Paper CBO - 501
Department of Life sciences, Patan

2. Content
• What is photoperiodism?
• Significance of photoperiodism
• Floral Induction
• Floral development
• Floral development :- genetics
• Flowering hormone

3. What is photoperiodism?
The response of an organism to seasonal
change in day length.
The plants in order to flower require a
certain day length I.e.,the relative length of
day and night which is called photoperiod.
The response of plants to the photoperiod
expressed in the from of flowering is called
photoperiodism.

4. The phenomenon of photoperiodism was first
discovered by Garner and Allard ( 1920,22) who
observed that the Biloxi variety of , Soybeans (
glycine max and 'Maryland Mammoth ' variety of
tobacco ( Nicotina tabacum) could be made to
flower only when the daily exposure to the light
was reduced below a certain critical duration and
after many complex experiment conduded that '
the relative length of the day is a factor of the first
importance in the growth and development of
plants.'

5. Depending upon the duration of the photoperiod they
Classified plants into three categories:-
①Short Day Plants ( SDP)
②Long Day Plants ( LDP)
③Day Neutral Plants

7. Short Day Plants ( SDP)
These plants require a relatively short day light
period ( usually 8- 10 hours ) and a continuos dark
period of about 14- 16 hours for subsequent
flower.
Some examples of these plants which are also
known as long - night - plants are Maryland
Mammoth variety of tobacco ( Nicotina tabacum)
Biloxi variety of Soybeans ( Glycine max .),
cocklebur ( xanthium Pennsylvanicum).

9. 1. In short day plants the dark period is critical
and must be continuous . If this dark period is
interrupted even with a brief exposure of red
light ( 660- 665 mu wavelength ) , the short day
plant will not flower.
2. Interruption of the light period by dark does not
have inhibitory effect on flowering in short day
plants.
3. Prolongation of the continuous dark period
initiates early flowering in short day plants.

11. Long Day Plants ( LDP)
These plants require a longer day light period (
usually 14 - 16 hours) in a 24 hours cycle for
subsequent flowering.
Some examples of these plants are which are also
called as short night plants are hyoscymas Niger
(Henbane) spinacea ( spinch) Beta vulgaris ( sugar
beet).
1. In long day plants the light period is critical .
2. A brief exposure in the dark period or the
prolongation of the light period stimulates
flowering in long day plants.

13. Day Neutral Plants
These plants flower in all photoperiods ranging
from 5 hours to 24 hours continuous exposure .
Some of the example of these plants are tomato ,
cotton , sunflower ,cucumber and certain varieties
of peas and tobacco
During recent years certain intermediate
categories of plants have also been recognized
.they are.

14. Importance of photoperiodism
A knowledge of the phenomenon of photoperiodism has
been of great practical importance in hybridization
experiments.
Although the floral hormone ' florigen ' has not yet been
isolated the isolation and characterization of this
hormone will be of utmost economic importance.
The phenomenon of photoperiodism is an excellent
example of physiological preconditioning (or after
effect) where an external factor ( I.e., the photoperiod
stimulus ) induces some physiological changes in the
plant the effect of which is not immediately visible .

15. Floral Induction
Floral Induction is physiological process that occurs
when the apical meristem becomes strong enough /
capable of developing flowers.
The process happens naturally in healthy plants , or ,
can be hurried up by gardeners through the
application of growth promoters.
 Various plants undergo flower initiation at various
times.
Floral Induction , sometimes referred to as flower
initiation , refers to the first stage of flowering , or the
onset of flower development , where the buds of a
plant became identificable start to form.

16. Floral Induction

17. Three types of genes regulate
floral development:
Studies of mutations have enabled identification
of three classes of genes that regulate floral
development:-
①Meristem identity genes
②Floral organ identity genes
③Cadastral genes

18. Meristem identity genes :--encode transcription factors that are
necessary for the initial Induction of organ identity genes.
• They are the positive regulators of floral organ identity in the
developing floral meristem.
Floral organ identity genes:- directly control floral identity.
• The proteins encoded by these genes are transcription factors
that likely control the expression of other genes whose products
are involved in the formation and /or function of floral organ.
Cadastral genes:-act as spatial regulators of the floral organ
identity genes by setting boundaries for their expression.

19. The four different types of floral organs are
initiated as separate whorls:-
Floral meristem initiate four different types of
floral organs:- sepals , petals , stamens, carpels.
These sets of organs are initiated in concentric
rings ,called whorls ,around the flanks of the
meristem.
The initiation of the innermost organs, the
carpels, consumes all of the meristematic cells in
the apical dome, and only the floral organ
primordia are present as the floral bud develops.

20. In the wild type Arabidopsis flower , the whorls
are arranged as follows :-
The first ( outermost ) whorl consist of four sepals , which
are green at maturity.
The second whorl is composed of four petals ,which are
white at maturity.
The third whorl contains six stamens ( the male
reproductive structure ) , two of which are shorter than
the other four.
The fourth whorl is a single complex organ , the gynocieum
or pistil ( the female reproductive structure) which is
composed of an ovary with two fused carpels ,each
containing numerous ovules and a short style capped with
a stigma.

22. Flowering
Hormone
 There is an
increasing evidence
to suggest that a
flowering hormone
exists in plants.
 Two important
evidences regarding
the existence of the
hormones are given
below :-

23. Flowering Hormone
There is a spatial separation of the site of stimulation
and the site of the response .
The buds do not perceive the stimulates for the
flowering.
The leaves , which perceive the stimuls transmit it to
the buds , obviously in the form of a flowering
hormone.
The existence of a flowering hormone is supported by
a number of grafting experiment .
A short day plant kept in long day conditions can be
induced to flower , if a properly photo induced plant is
grafted on to it.

24. References
• Plant Physiology by Taiz & Zeiger
• A Text Book of Plant Physiology by Verma V.
https //wikipedia . Com