New fluorescently labeled auxins exhibit promising anti-auxin activity

Abstract

The plant hormone auxin is a key player in the regulation of plant growth and development. Despite numerous studies devoted to understanding its role in a wide spectrum of physiological processes, full appreciation of its function is linked to a comprehensive determination of its spatio-temporal distribution, which plays a crucial role in its mode of action. Conjugation of fluorescent tracers to plant hormones enables sensitive and specific visualization of their subcellular and tissue-specific localization and transport in planta, which represents a powerful tool for plant physiology. However, to date, only a few fluorescently labeled auxins have been developed. We report the synthesis of four novel fluorescently labeled derivatives of indole-3-acetic acid (IAA) in the form of a conjugate with a nitrobenzoxadiazole (NBD) fluorophore together with validation of their biological activity. These compounds, unlike other previously reported auxins fluorescently labeled at N1 position (nitrogen of the indole ring), do not possess auxin activity but rather show dose-dependent inhibition of auxin-induced effects, such as primary root growth inhibition, root hair growth and the auxin reporter DR5::GUS expression. Moreover, the study demonstrates the importance of the character of the linker and optimal choice of the labeling site in the preparation of fluorescently labeled auxins as important variables influencing their biological activity and fluorescent properties.

Auxins and Cytokinins—The Role of Subcellular Organization on Homeostasis

“…Cell-specific sorting has been employed to gain more accurate insight into auxin [ 33 , 185 ] and CK [ 186 ] distributions in Arabidopsis root tips, and flow cytometric techniques for the sorting of organelles may soon provide a better view on subcellular distributions. Another possible approach for visualizing auxin and CK distributions at the cellular or subcellular level is using novel synthetic analogues labelled with 7-nitro-2,1,3-benzoxadiazole (NBD), for example, that have been recently developed to mimic native phytohormones in vivo [ 187 , 188 , 189 ]. A combination of all these methodologies with the use of mathematical modelling [ 78 , 122 , 190 ] to parameterize auxin homeostasis at cellular and subcellular levels will undoubtedly lead to far more detailed insights into the secrets of plant developmental control.…”

Seeing is better than believing: visualization of membrane transport in plants

“…In that respect it appears as if we have not yet fully used the potential of fluorescent transport substrates or click chemistry. In the future, structure-activity design will allow us to predict fluorophore positions and linker length [63,64] in order to direct uptake, stability and distribution of fluorescent substrates [96].…”

“…Bioactive auxin derivates tagged with fluorescein (IAA-FITC) or rhodamine (IAA-RITC) are distributed symplasticly and apoplasticly, respectively [35]. Hayashi et al designed fluorescent auxin analogs to be actively transported but to be inactive for auxin signaling [34 ], while very recently new fluorescently labeled auxins exhibit an anti-auxin activity [64]. The former is important because auxin signaling is known to influence auxin transporter expression and location [34 ].…”

What Has Been Seen Cannot Be Unseen—Detecting Auxin In Vivo

“…Nevertheless, the real overall chemical features of the derived molecules influenced by both the used linker and the fluorescent label have to be borne in mind. The position of the labelling site [ 152 ], and the character and the length of the linker [ 153 , 154 , 155 ] play a crucial role in the bioactivity of the new hormone analogues. Also, the choice of the fluorescent probe has to be considered.…”