Florigen – Definition, Meaning, Stages, Importance, Facts
Florigen is the mobile flowering hormone (FT protein) that triggers the transition from vegetative to reproductive growth. Synthesized in leaves, it travels through the phloem to the shoot apex, activating genes that induce flowering under suitable photoperiod and temperature conditions.
This Story also Contains
- What Is Florigen?
- Structure and Function of Florigen
- Synthesis And Regulation Of Florigen In Plants
- Genetic And Molecular Basis Of Florigen Function
- Interaction With Other Plant Hormones
- Environmental Factors Influencing Florigen Activity
- Florigen and Photoperiodism
- Florigen and Vernalisation
- Examples Of Florigen Function In Different Plant Species
- Florigen NEET MCQs (With Answers & Explanations)
- Recommended video on "Florigen"
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-
Property | Description |
Chemical Nature | Small polypeptide (protein) |
Molecular Identity | FT protein (FLOWERING LOCUS T) |
Mobility | Phloem-mobile signaling molecule |
Interaction partner | FD protein (forms FT-FD complex) |
Site of action | Shoot apical meristem |
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.
Gene | Function | Plant Model |
FT (FLOWERING LOCUS T) | Codes for florigen protein | Arabidopsis thaliana |
FD (FLOWERING LOCUS D) | Partners with FT for transcription | Arabidopsis |
Hd3a / RFT1 | Rice homologs of FT gene | Oryza sativa |
SFT | Tomato florigen | Solanum lycopersicum |
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.
Factor | Influence on Florigen |
Activates or represses FT gene expression | |
Temperature | Cold exposure (vernalisation) enhances florigen response |
Nutrients and water | Indirectly affect florigen synthesis by influencing photosynthesis |
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:
Plant | Gene | Photoperiod Type | Role |
Arabidopsis thaliana | FT | Lond-day | Promotes flowering |
Oryza sativa (Rice) | Hd3a | Short-day | Induces panicle formation |
Solanum lycopersicum (Tomato) | SFT | Day-neutral | Coordinates flowering with environment |
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
Shoot apex
Buds
Leaves
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.
Flowering Locus T
Ethylene
Phytochrome
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 ______.
Leaves, Intercalary meristem
Shoot apical meristem, Leaves
Intercalary meristem, Stomata
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:
Recommended video on "Florigen"
Frequently Asked Questions (FAQs)
Botanists had already begun experiments in grafting by the early part of the 20th century resulting in the discovery of florigen. In other words, scientists were able to show that some kind of signal from flowering plants can induce plants that are not flowering themselves to flower.
Photoperiodism—a phenomenon that is the basis of response to the length of day and night, acts as one of the prime regulators of florigen production. Florigen is produced only when a plant, either long or short days, has undergone an appropriate photoperiod.
The manipulation of florigen production and its signalling can control untimely flowering for better crop yield and enhanced agricultural productivity.
Mainly modelling plants have been used: Arabidopsis thaliana, rice, and tomato—all of them contributed much to the knowledge of current function and regulation of florigen.
Florigen is a phytohormone that induces flowering. It is synthesised in the leaves and moves into the inductive flowering shoot apical meristem.
