Plant Growth Regulators: Characteristics and Discovery

Recall how animals control and coordinate their activities and what helps them to respond to a stimulus.

Alike animals, plants do have control and coordinating system, more precisely called the plant growth regulators. Scientists took an era to discover and understand the functionality of the plant growth regulators. You may have observed bending of the tip of the shoot towards the light source on reception of light or wilting of leaves during a particular season. Let’s take a glance at the characteristics and discovery of plant growth regulators.

Plant Growth Regulators: Characteristics

Plant growth regulators can be defined as chemicals which signal to regulate and control the growth of plants. They are also referred to as plant hormones or phytohormones. Plant hormones are organic compounds which are either produced naturally within the plants or are synthesized in laboratories.  They profoundly control and modify the physiological processes like the growth, development, and movement of plants. In other words, plant growth regulators can accelerate as well as retard the rate of growth in plants.

Plants hormones are mainly responsible for –

  1. Differentiation and elongation of cells.
  2. Formation of leaves, flowers, and stems.
  3. Wilting of leaves.
  4. Ripening of fruit.
  5. Seed dormancy, etc.

Generally, there are five types of plant hormones namely, auxin, gibberellins (GAs), cytokinins, abscisic acid (ABA) and ethylene. In addition to these, there are more derivative compounds, both natural and synthetic, which also act as plant growth regulators.

Depending on the activity, plant growth regulators are classified into two recognized groups: one group which promotes the plant’s growth called plant growth promoters or biostimulants. The second group includes phytohormones that retard or inhibit the growth and are called plant growth inhibitors or bio inhibitors.

Auxin, gibberellins, and cytokinins belong to the plant growth promoters group where they help in cell division and differentiation, tropic growth, flowering, fruiting, and seed formation. Abscisic acid (ABA) belongs to the plant growth Inhibitors group which is responsible for dormancy and abscission in plants. Though ethylene is largely a big inhibitor, it is not included in both the groups and is commercially used for agriculture purposes.

Discovery of Plant Hormones

Though it was serendipity, initial steps of the discovery of major Plant growth regulators began with Charles Darwin and his son, Francis Darwin. They observed the growth of coleoptiles of canary grass towards the light source-phototropism. Followed by a series of experiments, they concluded the presence of a transmittable substance that influences the growth of canary grass towards the light. That transmittable substance was what we know as auxin which was isolated later by F.W. Went.

plant growth regulators

Later many scientists discovered and isolated different plant growth regulators. Gibberellins or gibberellic acid was formerly found in uninfected rice seedlings and was reported by E. Kurosawa. F. Skoog and Miller discovered another growth promoting substance named kinetin, which is now known as cytokinins.

To learn about functions of phytohormones and its discoveries, visit Byju’s.

Practise This Question

Cell elongation in internodal regions of the green plants takes place due to: