In recent years, substantial progress has been made in exploring auxin conjugation and metabolism, primarily aiming at indole-3-acetic acid (IAA). However, the metabolic regulation of another key auxin, phenylacetic acid (PAA), remains largely uncharacterized. Here, we provide a comprehensive exploration of PAA metabolism in land plants. Through LC-MS screening across multiple plant species and their organs, we identified four previously unreported endogenous PAA metabolites: phenylacetyl-leucine, phenylacetyl-phenylalanine, phenylacetyl-valine, and phenylacetyl-glucose. Enzyme assays, genetic evidence, crystal structures, and docking studies demonstrate that PAA and IAA share core metabolic machinery, revealing a complex regulatory network that maintains auxin homeostasis. Furthermore, our study of PAA conjugation with amino acids and glucose suggests limited compensatory mechanisms within known conjugation pathways, pointing to the existence of alternative metabolic routes in land plants. These insights advance our knowledge of auxin-specific metabolic networks and highlight the unique complexity within plant hormone regulation.

• Keywords
• Auxin, Gretchen Hagen 3, HPLC-MS/MS, conjugation, glucosyl ester, indole-3-acetic acid, metabolism, phenylacetic acid, plant,
• MeSH
• Phenylacetates * metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Metabolic Networks and Pathways * MeSH
• Plant Growth Regulators * metabolism   MeSH
• Embryophyta * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Phenylacetates * MeSH
• Indoleacetic Acids MeSH
• phenylacetic acid MeSH Browser
• Plant Growth Regulators * MeSH

The phytohormone auxin is a master regulator of plant growth and development in response to many endogenous and environmental signals. The underlying coordination of growth is mediated by the formation of auxin maxima and concentration gradients. The visualization of auxin dynamics and distribution can therefore provide essential information to increase our understanding of the mechanisms by which auxin orchestrates these growth and developmental processes. Several auxin reporters have been developed to better perceive the auxin distribution and signaling machinery in vivo. This review focuses on different types of auxin reporters and biosensors used to monitor auxin distribution and its dynamics, as well as auxin signaling, at the cellular and tissue levels in different plant species. We provide a brief history of each reporter and biosensor group and explain their principles and utilities.

• MeSH
• Indoleacetic Acids * MeSH
• Plant Growth Regulators * MeSH
• Plants MeSH
• Signal Transduction MeSH
• Plant Development MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Indoleacetic Acids * MeSH
• Plant Growth Regulators * MeSH

Plant hormones are master regulators of plant growth and development. Better knowledge of their spatial signaling and homeostasis (transport and metabolism) on the lowest structural levels (cellular and subcellular) is therefore crucial to a better understanding of developmental processes in plants. Recent progress in phytohormone analysis at the cellular and subcellular levels has greatly improved the effectiveness of isolation protocols and the sensitivity of analytical methods. This review is mainly focused on homeostasis of two plant hormone groups, auxins and cytokinins. It will summarize and discuss their tissue- and cell-type specific distributions at the cellular and subcellular levels.

• Keywords
• auxin, cellular level, cytokinin, phytohormone metabolism, phytohormone transport, subcellular level,
• MeSH
• Biological Transport MeSH
• Cytokinins metabolism   MeSH
• Plant Physiological Phenomena * MeSH
• Homeostasis * MeSH
• Intracellular Space metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Metabolic Networks and Pathways MeSH
• Organelles metabolism   MeSH
• Plant Growth Regulators metabolism   MeSH
• Plant Cells metabolism   MeSH
• Plant Development * MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Cytokinins MeSH
• Indoleacetic Acids MeSH
• Plant Growth Regulators MeSH

Auxins mediate various processes that are involved in plant growth and development in response to specific environmental conditions. Its proper spatio-temporal distribution that is driven by polar auxin transport machinery plays a crucial role in the wide range of auxins physiological effects. Numbers of approaches have been developed to either directly or indirectly monitor auxin distribution in vivo in order to elucidate the basis of its precise regulation. Herein, we provide an updated list of valuable techniques used for monitoring auxins in plants, with their utilities and limitations. Because the spatial and temporal resolutions of the presented approaches are different, their combination may provide a comprehensive outcome of auxin distribution in diverse developmental processes.

• Keywords
• auxin, auxin distribution, auxin signalling, auxin transport, direct visualization, indirect visualization, receptor, sensor,
• MeSH
• Arabidopsis metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Gene Expression Regulation, Plant MeSH
• Plant Development physiology   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Indoleacetic Acids MeSH