auxin

1. (botany, biochemistry) A class of plant growth substance (often called phytohormones or plant hormones) which play an essential role in coordination of many growth and behavioral processes in the plant life cycle.Examples: "In Arabidopsis roots, cold stress may reduce shootward auxin transport and alter the intracellular auxin gradient."; "SE onset depends on a complex network of interactions among plant growth regulators, mainly auxins and cytokinins, during the proembryogenic early stages, and ethylene and gibberellic and abscisic acids later in the development of somatic embryos."countableuncountable