Plant Growth Promoters

Plant growth promoters are substances that enhance the development of plants. They help in boosting the growth of the crop as well as its quality. The presence of different types of plant hormones such as cytokinins, gibberellins, and auxins in plant growth promoters helps in influencing better plant growth.

AUXIN

The first phytohormone to be discovered is the Auxin and it was discovered by the biologist Charles Darwin.

Auxins are one of the most important plant hormones. The chief naturally occurring auxin is indole-3 acetic acid – IAA and other related compounds. The term Auxin is derived from the Greek language meaning to grow.

These plant growth regulators are generally produced at the points of stems and roots from where they are transported to other parts of the plants. These plant hormones include both natural and synthetic sources. Indole-3-acetic acid and indole butyric acid are obtained from natural plant sources, whereas naphthalene acetic acid and 2, 4-dichlorophenoxyacetic acid are obtained from synthetic sources.

Functions of Auxins:

Facilitate flowering in plants
Used in the process of plant propagation.
Used by gardeners to keep lawns free from weeds.
Involved in the initiation of roots in stem cuttings.
Prevention of dropping of leaves and fruits at early stages.
Regulate xylem differentiation and assists in cell division.
Auxins are widely used as herbicides to kill dicot weeds.

Used to produce fruit without preceding fertilization.
Promote natural detachment (abscission) of older leaves and fruits.
Apical dominance may occur in which the growth of lateral buds is inhibited by the growth of apical buds. In such cases, the shoot caps may be removed.
These are produced by the apex of root and shoot.

GIBBERELLINS

Gibberellins are an extensive chemical family based on the ent-gibberellane structure. The first gibberellin to be discovered was gibberellic acid. Now there are more than 100 types of gibberellins and are mainly gathered from a variety of organisms from fungi to higher plants.

They are acidic and are denoted as follows – GA₁, GA₂, GA₃etc.

Functions of Gibberellins:

Delay senescence in fruits.
Break bud and seed dormancy.
Facilitate elongation of fruits such as apples and enhance their shape.
Used as the spraying agent to increase the yield of sugarcane by elongation of the stem.
Helps in increasing the crop yield by increasing the height in plants such as sugarcane and increase the axis length in plants such as grape stalks.

Involved in leaf expansion.
Promote bolting in cabbages and beet.
Used by the brewing industry to accelerate the malting process.
In young conifers, utilized to fasten the maturity period and facilitate early seed production
Gibberellins are acidic in nature.
It also delays senescence.

CYTOKININS

These are produced in the regions where cell division occurs; mostly in the roots and shoots. They help in the production of new leaves, lateral shoot growth, chloroplasts in leaves etc. They help in overcoming apical dominance and delay ageing of leaves.

Functions of Cytokinins:

Break bud and seed dormancy.
Promotes cell division and apical dominance.
Used in tissue culture to induce cell division in mature tissues.
Promotes nutrient mobilization that in turn assists delaying leaf senescence.
9. Involved in the formation of new leaves and chloroplast organelles within the plant cell.

Promotes the growth of the lateral bud.
They are used to keep flowers fresh for a longer time.
Facilitate adventitious shoot formation and lateral shoot growth.
Helps in delaying the process of ageing (senescence) in fresh leaf crops like cabbage and lettuce.
Used to induce the development of shoot and roots along with auxin, depending on the ratio.