Introduction to Plant Hormones

Study Notes

Plant hormones, also known as phytohormones, are signaling molecules that regulate plant growth and development.
These organic compounds are produced in one part of the plant and transported to another, where they exert their effects at very low concentrations.
Plant hormones influence a wide range of processes, including cell division, cell elongation, flowering, fruit development, and responses to environmental stresses.

Auxins: Primarily involved in phototropism (growth towards light), gravitropism (growth in response to gravity), apical dominance (inhibition of lateral bud growth), and cell elongation. IAA (Indole-3-acetic acid) is a crucial auxin.
Gibberellins: Stimulate stem elongation, seed germination, and fruit development. They also influence flowering and leaf senescence. GA (Gibberellic acid) is a prominent example.
Cytokinins: Promote cell division, leaf expansion, and delay senescence (aging). They are important in regulating shoot and root development. Zeatin is a common type.
Abscisic acid (ABA): Plays a crucial role in stress responses, such as drought tolerance, and seed dormancy. It inhibits growth and promotes stomatal closure.
Ethylene: A gaseous hormone that promotes ripening of fruits, abscission (leaf and fruit drop), and senescence. It influences responses to various stresses, such as flooding.

Plant hormones typically bind to specific receptor proteins within the plant cells.
These receptor-hormone complexes trigger signal transduction pathways, leading to changes in gene expression and cellular activities that affect plant morphology and physiology.
Some plant hormones act directly on target proteins or influence the activity of enzymes.

Plant hormones often interact in complex ways, with one hormone potentially activating or inhibiting the effects of another.
For example, auxins and cytokinins interact to regulate cell division and differentiation.
The interplay of various hormones in specific tissues and organs is critical in determining plant form and function.

Environmental cues, such as light, temperature, and water availability, can significantly influence plant hormone production and distribution.
Changes in these environmental factors often trigger specific hormonal responses to promote adaptive growth and survival.

Understanding plant hormones has led to applications in agriculture, such as controlling fruit ripening, promoting seed germination, and improving crop yields.
Synthetic plant hormones are used to regulate plant development in various horticultural and agricultural practices.

Continuous research is being conducted to fully understand the complex interactions of plant hormones and their effects on various physiological processes.