Question

Decapitation i.e. removal of shoot tips in a plant usually results in (a) inactivation of lateral buds (b) growth of lateral buds (c) cessation of plant growth (d) yellowing of leaves.

Short answer

Decapitation results in (b) growth of lateral buds.

Step-by-step solution

Understanding Decapitation

Decapitation in plants refers to the removal of the shoot tips. This is known to affect the growth process of the plants, especially regarding the lateral (side) buds. So, understanding what decapitation does to the lateral buds will help answer this question.

Role of Auxins

The shoot tips produce a hormone called auxin that inhibits the growth of lateral buds. When the shoot tip is removed (decapitation), the production of this hormone in that area is reduced or stopped.

Effect on Lateral Buds

With the reduced levels of auxin due to decapitation, the inhibition on the lateral buds is relieved and they start to grow. Therefore, decapitation results in the growth of lateral buds.

Key concepts

Lateral Bud Growth

Buds form along the sides of the stem of a plant and lie dormant until certain conditions induce their growth. One of these conditions involves decapitation, which is the removal of the main shoot tip. This fundamental pruning technique has a significant effect on a plant's growth pattern.

When a plant's shoot tip is removed, the dormant lateral buds are often stimulated to grow. Normally, growth is suppressed by a dominance exerted by the main shoot, but once this dominance is interrupted, for instance, by decapitation, the lateral buds may become active and start to grow. This alteration in the growth path is an adaptation mechanism that enhances the plant's survival following damage to its main axis. The activation of lateral bud growth can result in a bushier and more spread out form for the plant, which is beneficial both in natural environments and horticultural practices.

Role of Auxins in Plants

Auxins are a group of plant hormones that play a crucial role in coordinating various growth and behavioral processes in the plant life cycle. One well-recognized function of auxins is their involvement in maintaining apical dominance, a phenomenon where the central stem of the plant grows more strongly than the side stems.

They achieve this by inhibiting the growth of lateral buds while promoting cell elongation in the main shoot. Auxins are primarily produced in the shoot tips and are distributed downwards, causing a concentration gradient that results in the inhibition of the lateral buds. When the shoot tip is removed, causing decapitation, the auxin concentration drops, leading to the release of the buds from their dormant state. Understanding the dynamics of auxin production and distribution is vital for horticulturists and botanists alike, as it plays a key role in shaping plant architecture.

Plant Hormones

Plant hormones are essential chemicals in plants that, in small concentrations, regulate various functions such as development, growth, and responses to stimuli. Each group of plant hormones has unique roles. Besides auxins, there are gibberellins, which are important for stem elongation and seed germination; cytokinins, which promote cell division and are crucial in aging processes; and ethylene, a gas hormone that influences fruit ripening and leaf fall.

Another notable hormone is abscisic acid, which inhibits growth and promotes stomatal closure during water stress conditions. The balance and interaction between these hormones dictate the overall growth and adaptation of plants to their environment. Adjusting the levels of these hormones, such as through grafting or the application of artificial growth substances, lets gardeners and farmers shape the physical characteristics of plants to better meet human needs or adapt to environmental conditions.