Photoperiodism ,definition, history and classification.

1. PHOTOPERIODISM
AHMED MUSHTAQ
ROLL NO 10

2. Introduction
Photoperiodism is the response of a plant to relative strength
of light and dark periods to produce flower. The relative length of day and night to
which a plant is exposed is called the photoperiodism. It’s a photobiological
process- a process that involves absorption of light by a receptor(usually
pigments) that result the activation of that receptor which initiates the chemical
reaction that leads to general plant response.

3. History of Photoperiodism
Julien Tournois ( 1910)
Provides the first evidence regarding the effect of day length on
flowering. He found that Hemp(Cannabis sativus) flower if plant early in the spring and
does not flower if planted late in spring .
George Kleb (1918).
He was working with house leek plants, Found that flowering can be
induced by artificial illumination in midwinter in a green house ,although the normal time
of flowering us June.

4. Garner and Allard’s work
 The first clearly stated hypothesis on photoperiodism was given in
1920 by Garner and Allard. They observed that ‘Maryland Mammoth’
variety of Tobacco could be made to flower in summer by reducing the
light hours with artificial darkening. It could be made to remain
vegetative in winter by providing extra light

5. Classification of plants Based on PHOTOPERIODISM
 Short-day flowering plants
The plants that flowers when the day length is less than a certain critical
length are called short day-day plants (SDPs).these plants require the specific short duration
of light period of speeding up flowering.
For example:
 Rice
 Tobacco
 Soy bean

6. Long-day Flowering Plants(LDPs)
The plants that flower when a critical day length is exceeded are called long day plants.
These plants require exposure to longer duration of light periods before the flowering is
initiated .
For example
 Spinach
 Sugar beet
 Lettuce
 Pea
 Barley

7. Day-Neutral Flowering Plants
The plants whose not affected by either short or long duration of light are called
day neutral plants. These plants flower after a period of vegetative growth.
Example
 Tomato
 Cocumber
 Maize
 4 o clock