Bolting means the sudden elongation of the internode (the stem part between two nodes) just before a plant flowers. It is caused by the hormone gibberellin, and it turns a short "rosette" plant (like cabbage or beet, where leaves sit close to the ground) into a tall stem. Memory hook: "Bolt = Boot the internode up with Gibberellin."
Bolting: gibberellin makes the short internodes of a rosette plant (like cabbage or beet) elongate suddenly, raising a tall flowering stem before the plant flowers.
Your doubts, answered
What exactly is bolting?
Bolting is the fast elongation of the internodes (the stem gaps between leaves) that happens just before a plant flowers. In some plants the stem stays very short and the leaves look bunched near the ground; when bolting happens, this short stem shoots up tall. NCERT defines it as 'internode elongation just prior to flowering'.
Which hormone causes bolting?
Gibberellin (a gibberellic acid, GA) causes bolting. Gibberellins increase the length of the axis (stem), so they make the internodes stretch. In NEET, if a question says 'internode elongation before flowering' the answer is gibberellin.
What is a rosette plant, and why does it matter here?
A rosette plant is one whose stem is so short that the leaves grow in a tight circle close to the ground, like beet, cabbage and many similar plants. Because the internodes are normally very short, these plants show bolting very clearly: gibberellin makes the hidden short stem suddenly grow tall before flowering.
Is bolting the same as sugarcane stem elongation?
They use the same hormone but are used differently. In sugarcane, spraying gibberellin makes the stem (internodes) longer to store more sugar and raise yield. Bolting is the natural internode elongation before flowering in rosette plants like beet and cabbage. Both are gibberellin increasing the length of the axis, which is why NEET tests them together.
Does auxin or cytokinin cause bolting?
No. Auxin controls apical dominance and rooting; cytokinin drives cell division and delays senescence. Neither is the answer for 'internode elongation before flowering'. Only gibberellin does bolting, so do not pick auxin, cytokinin, ethylene or ABA for this.
⚠️ The NEET trap ✗ Choosing ethylene because it also causes stem/internode elongation in deep water rice. ✓ For bolting (internode elongation just before flowering) in rosette plants like beet and cabbage, the correct hormone is gibberellin. Ethylene elongates the internode/petiole in deep water rice, which is a different situation. 🧠 Bolting before flowering = Gibberellin. Deep water rice elongation = Ethylene. Do not mix the two.
Real NEET questions
ReNEET 2026
Which of the following plant growth regulators promotes internode elongation prior to flowering in cabbage?
A · Abscisic acid
B · Gibberellin ✓
C · Indole butyric acid
D · Ethephon
Solution: Gibberellin causes bolting, the elongation of the internodes just before flowering in rosette plants like cabbage. Abscisic acid is a growth inhibitor, indole butyric acid is an auxin used for rooting, and ethephon releases ethylene, so none of these gives the bolting effect.
NEET 2024
Spraying sugarcane crop with which of the following plant growth regulators, increases the length of stem, thus, increasing the yield?
A · Gibberellin ✓
B · Cytokinin
C · Abscisic acid
D · Auxin
Solution: Gibberellins increase the length of the axis (stem). Spraying sugarcane with gibberellin lengthens the internodes and raises yield by up to 20 tonnes per acre. Cytokinin drives cell division, ABA is an inhibitor, and auxin controls rooting and apical dominance, so they do not give this stem-elongation effect.
NEET 2020
Name the plant growth regulator which upon spraying on sugarcane crop increases the length of stem, thus increasing the yield of sugarcane crop.
A · Ethylene
B · Abscisic acid
C · Cytokinin
D · Gibberellin ✓
Solution: Gibberellin increases stem (internode) length, which is the same mechanism as bolting. In sugarcane this raises sugar yield. Ethylene, ABA and cytokinin do not produce this stem-elongation yield effect; ABA is in fact a growth inhibitor.
Solved Plant Growth and Development NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Bolting is the sudden elongation of the internodes just before flowering, caused by gibberellin, seen clearly in rosette plants like beet and cabbage.
Which hormone induces bolting in a rosette plant?
Gibberellin. NCERT states gibberellins promote bolting (internode elongation just prior to flowering) in beet, cabbages and many plants with rosette habit.
Why is bolting important for NEET?
NEET repeatedly links 'internode elongation before flowering' and 'increase in stem length' to gibberellin. Knowing bolting stops you from wrongly picking auxin, ethylene or cytokinin.
Can I induce bolting artificially?
Yes. Spraying a rosette plant with gibberellin can force bolting. NCERT even lists 'bolt a rosette plant' as a use of gibberellin in its exercise question.
