Odyssey of Auxin

Abstract

The history of plant biology is inexorably intertwined with the conception and discovery of auxin, followed by the many decades of research to comprehend its action during growth and development. Growth responses to auxin are complex and require the coordination of auxin production, transport, and perception. In this overview of past auxin research, we limit our discourse to the mechanism of auxin action. We attempt to trace the almost epic voyage from the birth of the hormonal concept in plants to the recent crystallographic studies that resolved the TIR1-auxin receptor complex, the first structural model of a plant hormone receptor. The century-long endeavor is a beautiful illustration of the power of scientific reasoning and human intuition, but it also brings to light the fact that decisive progress is made when new technologies emerge and disciplines unite.T he simple hormone related to tryptophan, indole-3-acetic acid (IAA or auxin), has probably been the most intensely studied molecule in plants as it impacts virtually every facet during their life cycle. In fact, a total failure in IAA production has not been reported for any plant alive. Thus, it is not surprising that auxin biology is one of the oldest fields of experimental plant research and that the underlying mechanisms of its action have captivated many generations of scientists.The regulation of growth and development by IAA is largely executed via the coordination of a triumvirate of complex processes: auxin metabolism, auxin translocation, and auxin response. The intricate maze of metabolic reactions related to IAA, encompassing its spatio-temporal patterns of biosynthesis, reversible conjugation, and degradation, is still unfolding. For example, significant progress has been made charting the biosynthetic pathways by a combination of genetic and biochemical approaches, which revealed the operation of at least five different routes to IAA. Our current understanding of the redundant metabolic processes that determine auxin supply has recently been reviewed (Woodward and Bartel 2005;Delker et al. 2008;Chandler 2009). The delivery of auxin from its biosynthetic sources to its sites of perception follows two major, unrelated modes of transportation: rapid longdistance movement via the phloem sap, and slower cell-to-cell distribution over shorter distances. The latter process is unique among

Analytical History of Auxin

“…The auxins include compounds such as indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), phenylacetic acid, and 4-chloroindole-3-acetic acid (4-Cl-IAA). Abel and Theologis (2010) noted that ''The history of plant biology is inexorably intertwined with the conception and discovery of auxin…'' and in the history of auxin the critical milestones from compound isolation to function would likely never have been accomplished without quantitative assays. As the history of plant biology is inexorably intertwined with auxin, so too is the history of auxin measurements linked to developments in the science of analytical biochemistry and chemistry.…”

Oxidative and antioxidative responses in the wheat-Azospirillum brasilense interaction

“…The plant growth-promoting effect of Azospirillum brasilense is mainly attributed to the production of the phytohormone indole-3-acetic acid (IAA) (Dobbelaere et al 1999), known to be the most abundant naturally occurring auxin. Notably, IAA is involved in the coordination of plant growth and development (Abel and Theologis 2010).…”

Growth and yield response of two hybrid rice cultivars to ATONIK plant growth regulator in a Tropical environment

“…Furthermore, PGRs regulate the amount, type and direction of plant growth with remarkable accomplishments of improved plant development and enhanced yield in several crops been documented (Shah et al 2006;Emongor 2007). For instance, Auxin, a PGR, regulators cell elongation, tissue swelling, cell division and formation of adventitious roots, among others (Woodward and Bartel 2005;Abel and Theologis 2010). Similarly, Gibberellic acid, another PGR, participates in the regulation of many growth and development processes in various plants, including rice (Richards et al 2001;Sakamoto et al 2004;Sun 2004).…”