Florigen – Definition, Meaning, Stages, Importance, Facts

What Is Florigen?

Florigen is a plant hormone or flowering signalling molecule. Mikhail Chailakhyan, as far back as the 1930s, hypothesized that there must be something produced in the leaves, which is mobile and moves to the shoot apical meristem, inducing flowering in plants.

Only recently, this concept has been confirmed by experimental works on grafting and identification of genes like FT of Arabidopsis. It thus plays a critical role in the plants: florigen mediates the vegetative growth-to-reproductive development transition and, in doing so, ensures flowering takes place in response to environmental signals for photoperiod and temperature to achieve optimum reproductive success.

Structure and Function of Florigen

The structure of florigen is discussed below-

Synthesis And Regulation Of Florigen In Plants

Florigen synthesis occurs in leaves under certain photoperiod conditions. The control of florigen biosynthesis is exerted by genes encoding a mobile flowering signal, FLOWERING LOCUS T (FT).

Role Of Florigen In The Flowering Process

Induction of flowering in plants

This florigen moves from leaves into the shoot apical meristem, inducing the switch from vegetative development to reproductive development.

Transport and signalling pathways of florigen

Florigen moves complexes with proteins like FD through phloem, and through it, flowering genes are turned on.

Genetic And Molecular Basis Of Florigen Function

The FT gene and its paralogs consist of one essential genetic determinant regulating the synthesis and action of florigen.

Interaction With Other Plant Hormones

Florigen acts synergistically with gibberellins during flowering. The distribution and the activity of florigen can also be controlled by cytokinins.

• Gibberellins (GA): Enhance flowering in conjunction with florigen.

• Cytokinins: Influence florigen distribution and activation.

• Auxins: Support transport and meristem differentiation.

Environmental Factors Influencing Florigen Activity

Light, temperature, and day length—through which florigen synthesis and movement are guided—are major environmental factors.

Florigen and Photoperiodism

The ability of florigen to mediate plants' responses to daylight duration makes it a factor in photoperiodic flowering.

• In long-day plants, florigen synthesis increases with longer light exposure.

• In short-day plants, it peaks when the dark period exceeds a critical duration.

Florigen and Vernalisation

• The ability of florigen to mediate plants' responses to daylight duration makes it a factor in photoperiodic flowering.

• After vernalisation, FT gene can be freely expressed, enabling florigen synthesis and flowering.

Examples Of Florigen Function In Different Plant Species

Some of the examples of florigen in different plant species:

Florigen NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Structure and functions of florigen

• Interaction with other plant hormones

Practice Questions for NEET

Q1. The flowering hormone Florigen is perceived by

1. Shoot apex

2. Buds

3. Leaves

4. Flowers

Correct answer: 4) Flowers

Explanation:

Florigen is a hypothesized hormone-like substance responsible for promoting and regulating flowering in plants. It is produced in the leaves, which perceive the required light/dark duration (inductive photoperiod), and then migrates to the shoot apices to trigger flowering. Leaves serve as the site for photoperiod perception, and florigen is transported from the leaves to the apical meristem to induce flowering. Grafting experiments in plants like cocklebur have also shown that this floral hormone can be translocated between plants. This highlights its role as a mobile flowering signal critical for plant reproduction.

Hence the correct answer is option 4) flowers.

Q2. _______ , a florigen that stimulates flowering, is a positive regulator of H+-ATPase and blue-light-induced stomatal opening.

1. Flowering Locus T

2. Ethylene

3. Phytochrome

4. Abscisic acid

Correct answer: 1) Flowering Locus T

Explanation:

FLOWERING LOCUS T (FT) is a florigen that stimulates flowering is expressed in the guard cells and regulates the stomatal opening. This pigment is involved in photoperiodism and is referred to as a phytochrome.

Hence, the correct answer is option 1) Flowering Locus T.

Q3. Florigen is synthesized in ____and transported to the ______.

1. Leaves, Intercalary meristem

2. Shoot apical meristem, Leaves

3. Intercalary meristem, Stomata

4. Leaves, Shoot apical meristem

Correct answer: 4) Leaves, Shoot apical meristem

Explanation:

Plants respond to the systemic signal known as florigen to start flowering (Chailakhyan, 1936). It is synthesized in the leaves and transported to the shoot apical meristem (SAM), where it stimulates the transition to flowers.

Hence, the correct answer is option 4) Leaves, shoot apical meristem.

Also Read:

• MCQs on Florigen

• Auxin Biosynthesis

• Factors affecting plant growth

Recommended video on "Florigen"