Photoperiodism: Plant Responses, Flowering, Light Signals

What Is Photoperiodism?

Photoperiodism is the biological response of any living thing toward the comparative length of the light periods. It is a fundamental mechanism by which organisms synchronise their growth and development to environmental cycles resulting from seasonal changes. The photoperiodic control in plants mainly regulates flowering and is, therefore, referred to as photoperiodic flowering.

Photoperiodism In Plants

Plants have specialised photoreceptor proteins called phytochromes and cryptochromes which enable them to keep track of the periodic changes in duration of light and darkness.

• Phytochrome – sensitive to red (R) & far-red (FR) light

• Cryptochrome – sensitive to blue light

These photoreceptors measure night length which is the true determinant of flowering.

Types of Plants Based on Photoperiodic Response

Three broad categories can thus be made based on their response to photoperiod:

Long-Day Plants (LDP)

• Flowering is induced with a longer exposure to light.

• Examples: Radish, Spinach, Sugar beet

Short-Day Plants (SDP)

• Flowering is induced with a shorter exposure to light.

• Examples: Sunflower, Rice, Soybeans, Tobacco

Day-Neutral Plants (DNP)

• Flower irrespective of day length.

• Flowering depends on other factors, such as age or an external stimulus

• Examples: Rose, Tomato, Cucumber

Mechanism of Photoperiodic Flowering

The mechanism of photoperiodic flowering involves the following process:

• Light/dark signal perception by photoreceptors

• Activation of phytochrome-cryptochrome photoreceptors

• Synthesis of the florigen (FT protein)

• Transport of florigen to the shoot apical meristem

• Activation of flowering genes and the development of flowers

• Conversion of vegetative meristem to floral meristem.

Photoperiodism In Animal

Animals use photoperiod to regulate:

• In photoperiodism, seasonal changes induce modifications of behaviour and developmental strategies in many animals, especially at higher latitudes.

• Other animals turn on their behaviour according to the season for certain behaviours less obvious than in plants.

• Such animals include seasonally breeding animals, singing birds during longer days, and insects in a dormant state known as diapause.

Significance Of Photoperiodism

The significance of photoperiodism in plants and animals is:

• Photoperiodism is a process critical to an organism's very survival and adaptation to its environment.

• This gives plants the ability to flower at the appropriate time of the year so that successful reproduction and seed production occurs.

In animals also, photoperiodism helps regulate behaviour where it will coincide with activities such as migration, hibernation, and reproduction with seasons.

Differences Between LDP, SDP & DNP (Comparison Table)

Difference between long-day plants (LDP), short-day plants (SDP) and day-neutral plants (DNP) is given in the table below:

Photoperiodism NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Types of Plants based on photoperiodic response

• Long-day plants vs Short-day plants vs Day-neutral plants

• Mechanism of Photoperiodic flowering

Practice Questions for NEET

Q1. Which of the following plants belong to long short Day plants (LSDP)?

1. Hyoscyamus niger

2. Bryophyllum cestrum

3. Oryza sativa

4. Zea mays

Correct answer: 2) Bryophyllum cestrum

Explanation:

Long short Day plants (L-SDP) -

Plants require long photoperiods for floral initiation and short photoperiods for blossoming. When they get more than 12 hours of light per day—typically 14–16 hours—they bloom. Another name for them is short night plants. Plants flower between summer and autumn. Eg. Bryophyllum Cestrum

Hence, the correct answer is option 2) Bryophyllum cestrum.

Q2. Photoperiodism is the

1. Response of plants to the changing environmental conditions

2. Response of plant to the low temperature treatment expressed in the form of flowering

3. Response of plants to the photoperiod expressed in the form of flowering

4. Response of plants to the quality of light expressed in the form of seed germination

Correct answer: 4) Response of plants to the photoperiod expressed in the form of flowering

Explanation:

The response of plants to the photoperiod expressed in the form of flowering is called photoperiodism. Photoperiodism is controlled by photoreceptor proteins like phytochromes and cryptochromes, which sense the duration of light and dark periods. Plants are classified based on their flowering response into short-day, long-day, and day-neutral plants. This mechanism helps plants synchronize their reproductive cycles with favorable environmental conditions.

Hence, the correct answer is option 3) the response of plants to the photoperiod expressed in the form of flowering.

Q3. Long day plants produces flowers when they exposed to

1. Any duration of light

2. Light period longer than a critical day length

3. Light period longer than 12 hours

4. Light period shorter than a critical day length

Correct answer: 2) Light period longer than a critical day length

Explanation:

The critical photoperiod is the length of time that must be exposed to light for some plants to flower. This varies among species and is important for their reproduction.
Key Terms
Long-Day Plants: These plants need a light period longer than a certain number of hours (the critical photoperiod) to begin flowering. They tend to bloom in late spring or early summer when days are longer.
Examples: Some common long-day plants are:
Spinach
Lettuce
Some Wheat Types
Light exposure past the critical photoperiod causes these plants to begin producing flowering hormones, causing the transition from vegetative growth to flowering. Knowledge of critical photoperiods is critical for agriculture as it determines the timing of planting schedules and crop yields.

Hence, the correct answer is option 2) Light period longer than a critical day length.

Also Read:

• MCQs on Photoperiodism in Plants

• Auxin Biosynthesis

• Factors Affecting Plant Growth

Recommended Video on Photoperiodism