Effect of Auxin (IAA) on the Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

Abstract

<jats:p>In contrast to the well-studied effect of auxin on the plasma membrane K+ channel activity, little is known about the role of this hormone in regulating the vacuolar K+ channels. Here, the patch-clamp technique was used to investigate the effect of auxin (IAA) on the fast-activating vacuolar (FV) channels. It was found that the macroscopic currents displayed instantaneous currents, which at the positive potentials were about three-fold greater compared to the one at the negative potentials. When auxin was added to the bath solution at a final concentration of 1 µM, it increased the outward currents by about 60%, but did not change the inward currents. The imposition of a ten-fold vacuole-to-cytosol KCl gradient stimulated the efflux of K+ from the vacuole into the cytosol and reduced the K+ current in the opposite direction. The addition of IAA to the bath solution with the 10/100 KCl gradient decreased the outward current and increased the inward current. Luminal auxin reduced both the outward and inward current by approximately 25% compared to the control. The single channel recordings demonstrated that cytosolic auxin changed the open probability of the FV channels at the positive voltages to a moderate extent, while it significantly increased the amplitudes of the single channel outward currents and the number of open channels. At the positive voltages, auxin did not change the unitary conductance of the single channels. We suggest that auxin regulates the activity of the fast-activating vacuolar (FV) channels, thereby causing changes of the K+ fluxes across the vacuolar membrane. This mechanism might serve to tightly adjust the volume of the vacuole during plant cell expansion.</jats:p>

An auxin signaling network translates low-sugar-state input into compensated cell enlargement in the fugu5 cotyledon

“…Vacuoles are not only the largest organelles of mature plant cells, they also play pivotal roles in plant growth and development, notably through the regulation of turgor pressure. This might involve vacuole acidification through the V-ATPase, downstream of auxin signaling [ 45 , 46 ]. To investigate the putative contribution of V-ATPase-dependent vacuole acidification on fugu5 CCE, we analyzed the vha-a2 vha-a3 fugu5–1 triple mutant.…”

“…More recently, it has been reported that plant vacuoles significantly increase their volume (ca. two-fold) upon incubation with 1 μM IAA [ 45 , 46 ], linking auxin and vacuolar acidification, and providing insights into vacuole volume regulation during post-mitotic plant cell expansion.…”

“…Based on the involvement of IBA in cotyledon development, we have proposed that IBA might be a key metabolite driving CCE [ 22 , 25 ]. Also, treatment with IAA (1 μM) causes a significant increase in the volume of red beet taproot vacuoles [ 45 , 46 ]. Thus, to elucidate the mechanism of class II CCE, we performed molecular genetic analyses in a fugu5 mutant background combined with mutants with defects in IBA-to-IAA conversion, IBA efflux, IAA signaling, or V-ATPase activity.…”

Some New Methodological and Conceptual Aspects of the “Acid Growth Theory” for the Auxin Action in Maize (Zea mays L.) Coleoptile Segments: Do Acid- and Auxin-Induced Rapid Growth Differ in Their Mechanisms?

“…It has also been shown that apart from the posttranslational, auxin-dependent up-regulation of both the K + uptake channels and the PM H + -ATPases, auxin also regulates their expression [ 28 , 31 ]. Quite recently, it was also shown that the SV (slow vacuolar) and FV (fast vacuolar) channels, which represent the conductance of the major cations across the tonoplast, are involved in the IAA-induced volume changes of the vacuoles [ 32 , 33 ].…”

Fusicoccin (FC)-Induced Rapid Growth, Proton Extrusion and Membrane Potential Changes in Maize (Zea mays L.) Coleoptile Cells: Comparison to Auxin Responses

“…The patch-clamp experiments that were recently performed by Burdach et al [ 27 , 28 ] should also be mentioned. These authors showed that the SV (slow vacuolar) and FV (fast vacuolar) channels, which represent the conductance of the major cations across the tonoplast, are involved in the IAA-induced volume changes of the vacuoles.…”