2. Classification of plants and photoperiodism
Introduction:
Photoperiodism:
• It is physiological reaction of organism to the length of day or night.
• It occurs in plant and animals. Photoperiodism can also be defined as
the developmental responses of the plants to the relative length of light
and dark periods.
3. Cont…
• Many flowering plants (angiosperms)use a photoreceptor protein, such
as phytochrome and cryptochrome to sense seasonal changes in night
length or photoperiod which they take as signal to flower.
• Phytochrome:
• Phytochrome come into two forms,pr and pfr.Red light which is
present during the day convert phytochromes to its active form pfr.
4. Cont…
• Cryptochrome:
• Are another type of photoreceptor that is important in photoperiodism.
Cryptochromes absorb blue light and UV-A.
In further subdivision obligate photoperiodic plants absolutely require a
long or short enough night before flowering, whereas facultative
photoperiodic plants are more likely to flower under one condition.
5. Classification of plant
Short day Plants:
• The plant that flowers when day length is less than a certain critical
length are called short day plants.
• These plants require specific short duration of light. These are actual
long night plants.
• They need darkness more than a critical length. They can flower in 24
hours.
6. Cont…
• For example xanthimum flower under photoperiod less than 15 and
half.The duration of light should be less than this critical time.
• Other example of short day plants are Biloxi soyabean,tabacoo and
strawberry.
7. Cont…
Long day plants:
• The plant that flowers when day length is more than a certain critical
length are called long day plants.
• Dark period is not important for them .It mean they can flower even
they are exposed to 24 hours light.
• Examples:
• Cabbage,spring wheat and spring barley.
8. Cont..
Day neutral plants:
• These are also known as day length in different plants such plants
flower under any photoperiod.
• Its examples are tomato,cucumber,maize,cotton and garden pea.
