Abstract
BackgroundAuxin (IAA) is a central player in plant cell growth. In contrast to the well-established function of the plasma membrane in plant cell expansion, little is known about the role of the vacuolar membrane (tonoplast) in this process.ResultsIt was found that under symmetrical 100 mM K+ and 100 μM cytoplasmic Ca2+ the macroscopic currents showed a typical slow activation and a strong outward rectification of the steady-state currents. The addition of IAA at a final concentration of 1 μM to the bath medium stimulated the SV currents, whereas at 0.1 and 10 μM slight inhibition of SV currents was observed. The time constant, τ, decreased in the presence of this hormone. When single channels were analyzed, an increase in their activity was recorded with IAA compared to the control. The single-channel recordings that were obtained in the presence of IAA showed that auxin increased the amplitude of the single-channel currents. Interestingly, the addition of IAA to the bath medium with the same composition as the one that was used in the patch-clamp experiments showed that auxin decreased the volume of the vacuoles.ConclusionsIt is suggested that the SV channels and the volume of red beet taproot vacuoles are modulated by auxin (IAA).
Highlights
Auxin (IAA) is a central player in plant cell growth
In the presence of indole-3-acetic acid (IAA), the volume of the vacuoles that had been incubated in bath medium without K+ increased by 20%
When the vacuoles were incubated in the presence of 20 or 100 mM K+, their volume was about 3% lower compared to the first value
Summary
Auxin (IAA) is a central player in plant cell growth. In contrast to the well-established function of the plasma membrane in plant cell expansion, little is known about the role of the vacuolar membrane (tonoplast) in this process. According to the so-called “acid growth theory”, auxin activates the PM H+-ATPase, which acidifies the apoplast and causes the activation of the enzymes that are involved in cell wall loosening (for a review see [1]) It is well established, at least in maize coleoptile cells, that auxin-induced growth involves K+ uptake through voltage-dependent, inwardly rectifying K+ channels (ZMK1, Zea mays K+ channel 1), the activity of which contributes to water uptake and to cell expansion [2, 3]. As these authors showed, auxin inhibited the growth of the root epidermal cells This finding was used by Dünser and Kleine-Vehn [9] to propose the “acid growth balloon theory” according to which plant growth is the interplay between the intracellular space-filling “vacuolar balloon” and the required extracellular cell wall acidification/loosening
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