https://orcid.org/0000-0002-0384-490X
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David G. Robinson, Chris Hawes, Stefan Hillmer, Gerd Jürgens, Claus Schwechheimer, York-Dieter Stierhof, Corrado Viotti, Auxin and Vesicle Traffic, Plant Physiology, Volume 176, Issue 3, March 2018, Pages 1884–1888, https://doi.org/10.1104/pp.17.01510
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Questionable Evidence for Auxin-Carrying Secretory Vesicles
Dear Editor,
The plant hormone auxin (indole-3-acetic acid [IAA]) controls almost every aspect of plant development and growth. Auxin is transported within the plant from cell to cell through auxin transporters, including the PIN-FORMED (PIN) efflux transporters (Geisler et al., 2017; Naramoto, 2017) and ABCB transporters (Borghi et al., 2015; Geisler et al., 2017). These transporters can operate independently of one another or in concert (Geisler et al., 2017). They are transmembrane proteins that are delivered to the plasma membrane (PM) by vesicle transport. Their orientation in the vesicle membrane during intracellular transport could potentially lead to the vesicles accumulating auxin and consequently directly cause auxin to be released into the extracellular space upon vesicle fusion with the PM.
This hypothetical scenario has inspired the idea that auxin transport resembles the release of neurotransmitters from synaptic vesicles during neurotransmission in animals and led to the premise of “plant synapses.” Consequently, the term “Plant Neurobiology” arose about a decade ago (Brenner et al., 2006) to promulgate these concepts and the notion that plants are not so different from animal cells in terms of signal transduction. Although the usage has been heavily criticized by many plant scientists (Alpi et al., 2007; Rehm and Gradmann, 2010), the existence of plant synapses is still promoted by some (Balu¡ka et al., 2009; Balu¡ka and Mancuso, 2013).
