Question

Growth of lateral branches is promoted by
A. Removal of axillary buds
B. Auxin application over the decapitated apex
C. Auxin application over apical bud
D. Removal of apical bud

Answer 1

Hint: A phenomenon in which the central stem is dominant and lateral stems are suppressed is known as Apical dominance. It is due to the plant hormone known as Auxin. It is produced in the tip of the axillary bud and the shoot. Auxin concentration decreases when the apical bud is removed which results in the growth of lateral branches.

Complete answer:
> Option A- Removal of axillary buds
The axillary bud also known as the lateral bud is an embryonic or organogenic shoot that is located in the axil of a leaf. Each bud has the potential to form shoots and is specialized to produce either vegetative shoots (stems and branches) or reproductive shoots (flowers). Once formed, either a bud remains dormant for some time or shoots immediately.

> Option B- Auxin application over the decapitated apex
The effect of auxin application on decapitation is induced branching in WT (cv Parvus), rms1-1, and rms2-2 plants. It is due to the estimated position of the axillary shoot apex, to an accuracy of 1 mm

> Option C- Auxin application over apical bud
The apical bud produces a hormone known as aa auxin, (IAA). It inhibits the growth of the lateral buds further down on the stem towards the axillary bud. It is predominantly produced in the growing shoot apex and is transported throughout the plant via the phloem and diffuses into lateral buds which prevents elongation.

> Option D- Removal of apical bud
During the removal of the apical bud, the IAA concentration lowers and allows the lateral buds to grow. It produces new shoots, which compete to become the lead growth.

Hence, the correct answer is option (D).

Note: Apical control refers to the inhibition of a lateral branch growth by shoots above it (distal shoots). When the distal shoots are cut off to remove apical control, the lateral branch grows larger and may bend upwards. Apical control begins when new lateral buds grow after passing through a period of dormancy.