Stomatal opening is the result of K+-salt accumulation in guard cells. Potassium uptake in these motor cells is mediated by voltage-dependent, K+-selective ion channels. Here we compare the in-vitro properties of two guard-cell K+-channel alpha-subunits from Arabidopsis thaliana (L.) Heynh. (KAT1) and Solanum tuberosum L. (KST1) after heterologous expression with the respective K+-transport characteristics' in their mother cell. The KAT1 and KST1 subunits when expressed in Xenopus oocytes shared the basic features of the K+-uptake channels in the corresponding guard cells, including voltage dependence and single-channel conductance. Besides these similarities, the electrophysiological comparison of K+ channels in the homologous and the heterologous expression systems revealed pronounced differences with respect to modulation and block by extracellular cations. In the presence of 1 mM Cs+, 50% of the guard-cell K+-uptake channels (GCKCl(in)) in A. thaliana and S. tuberosum, were inhibited upon hyperpolarization to -90 mV. For a similar effect on KAT1 and KST1 in oocytes, voltages as negative as -155 mV were required. In contrast, compared to the K+ channels in vivo the functional alpha-subunit homomers almost lacked a voltage-dependent block by extracellular Ca2+. Similar to the block by Cs+ and Ca2+, the acid activation of the alpha-homomers was less pronounced in oocytes. Upon acidification the voltage-dependence shifted by 82 and 90 mV for GCKCL(in), in A. thaliana and S. tuberosum, respectively, but only by 25 mV for KAT1 and KST1. From the differences in K+-channel modulation in vivo and after heterologous expression we conclude that the properties of functional guard-cell K+-uptake channels result either from the heterometric assembly of different alpha-subunits or evolve from cell-type-specific posttranslational modification.
%0 Journal Article
%1 RN1233
%A Brüggemann, L.
%A Dietrich, P.
%A Dreyer, I.
%A Hedrich, R.
%D 1999
%J Planta
%K arabidopsis myOwn
%N 3
%P 370-376
%R DOI 10.1007/s004250050494
%T Pronounced differences between the native K
channels and KAT1 and KST1 α-subunit homomers of guard cells
%U /brokenurl#<Go to ISI>://WOS:000078274900006
%V 207
%X Stomatal opening is the result of K+-salt accumulation in guard cells. Potassium uptake in these motor cells is mediated by voltage-dependent, K+-selective ion channels. Here we compare the in-vitro properties of two guard-cell K+-channel alpha-subunits from Arabidopsis thaliana (L.) Heynh. (KAT1) and Solanum tuberosum L. (KST1) after heterologous expression with the respective K+-transport characteristics' in their mother cell. The KAT1 and KST1 subunits when expressed in Xenopus oocytes shared the basic features of the K+-uptake channels in the corresponding guard cells, including voltage dependence and single-channel conductance. Besides these similarities, the electrophysiological comparison of K+ channels in the homologous and the heterologous expression systems revealed pronounced differences with respect to modulation and block by extracellular cations. In the presence of 1 mM Cs+, 50% of the guard-cell K+-uptake channels (GCKCl(in)) in A. thaliana and S. tuberosum, were inhibited upon hyperpolarization to -90 mV. For a similar effect on KAT1 and KST1 in oocytes, voltages as negative as -155 mV were required. In contrast, compared to the K+ channels in vivo the functional alpha-subunit homomers almost lacked a voltage-dependent block by extracellular Ca2+. Similar to the block by Cs+ and Ca2+, the acid activation of the alpha-homomers was less pronounced in oocytes. Upon acidification the voltage-dependence shifted by 82 and 90 mV for GCKCL(in), in A. thaliana and S. tuberosum, respectively, but only by 25 mV for KAT1 and KST1. From the differences in K+-channel modulation in vivo and after heterologous expression we conclude that the properties of functional guard-cell K+-uptake channels result either from the heterometric assembly of different alpha-subunits or evolve from cell-type-specific posttranslational modification.
@article{RN1233,
abstract = {Stomatal opening is the result of K+-salt accumulation in guard cells. Potassium uptake in these motor cells is mediated by voltage-dependent, K+-selective ion channels. Here we compare the in-vitro properties of two guard-cell K+-channel alpha-subunits from Arabidopsis thaliana (L.) Heynh. (KAT1) and Solanum tuberosum L. (KST1) after heterologous expression with the respective K+-transport characteristics' in their mother cell. The KAT1 and KST1 subunits when expressed in Xenopus oocytes shared the basic features of the K+-uptake channels in the corresponding guard cells, including voltage dependence and single-channel conductance. Besides these similarities, the electrophysiological comparison of K+ channels in the homologous and the heterologous expression systems revealed pronounced differences with respect to modulation and block by extracellular cations. In the presence of 1 mM Cs+, 50% of the guard-cell K+-uptake channels (GCKCl(in)) in A. thaliana and S. tuberosum, were inhibited upon hyperpolarization to -90 mV. For a similar effect on KAT1 and KST1 in oocytes, voltages as negative as -155 mV were required. In contrast, compared to the K+ channels in vivo the functional alpha-subunit homomers almost lacked a voltage-dependent block by extracellular Ca2+. Similar to the block by Cs+ and Ca2+, the acid activation of the alpha-homomers was less pronounced in oocytes. Upon acidification the voltage-dependence shifted by 82 and 90 mV for GCKCL(in), in A. thaliana and S. tuberosum, respectively, but only by 25 mV for KAT1 and KST1. From the differences in K+-channel modulation in vivo and after heterologous expression we conclude that the properties of functional guard-cell K+-uptake channels result either from the heterometric assembly of different alpha-subunits or evolve from cell-type-specific posttranslational modification.},
added-at = {2024-02-14T14:38:32.000+0100},
author = {Brüggemann, L. and Dietrich, P. and Dreyer, I. and Hedrich, R.},
biburl = {https://www.bibsonomy.org/bibtex/28eace0ee0b09d786dd466ae7d0e1a96a/rainerhedrich_2},
doi = {DOI 10.1007/s004250050494},
interhash = {5d724658040fef1b9105c87c1bac7c26},
intrahash = {8eace0ee0b09d786dd466ae7d0e1a96a},
issn = {0032-0935},
journal = {Planta},
keywords = {arabidopsis myOwn},
note = {161ec
Times Cited:33
Cited References Count:49},
number = 3,
pages = {370-376},
timestamp = {2024-02-14T14:38:32.000+0100},
title = {Pronounced differences between the native K
channels and KAT1 and KST1 α-subunit homomers of guard cells},
type = {Journal Article},
url = {/brokenurl#<Go to ISI>://WOS:000078274900006},
volume = 207,
year = 1999
}