Discovery, metabolism and importance of auxins and cytokinins: The plant growth regulators

Auxins and cytokinin are two fundamental classes of plant growth regulators that play crucial roles in various aspects of plant development and physiology. This article provides an overview of the discovery, metabolism, and importance of auxins and cytokinin in plant growth and development. Auxins, initially discovered in the early 20th century, are primarily known for their involvement in regulating cell elongation, tropisms, apical dominance, and root development. Indole-3-acetic acid (IAA) is the most prominent naturally-occurring auxin. Auxins are synthesized in young tissues, including shoot apices and developing seeds, and are transported polarly within plants. Cytokinin, discovered later than auxins, is essential for cell division, shoot formation, leaf senescence, and overall plant growth. Adenine derivatives, such as zeatin, kinetin, and isopentenyl adenine, are commonly found in cytokinin. Like auxins, cytokinins are synthesized in actively dividing tissues, primarily in root tips and developing embryos. Understanding the metabolic pathways and signaling mechanisms of auxins and cytokinin has paved the way for their practical applications in agriculture, horticulture, and plant biotechnology. The precise manipulation of auxin and cytokinin levels through exogenous application or genetic engineering has been utilized to enhance crop productivity, control plant growth and development, and improve stress tolerance in plants.