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Vacuolar Na+/H+ Antiporters in Arab...

Zhang, Shiqi.

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Vacuolar Na+/H+ Antiporters in Arabidopsis thaliana: Cation Selectivity and Biological Functions.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Vacuolar Na+/H+ Antiporters in Arabidopsis thaliana: Cation Selectivity and Biological Functions./
Author:	Zhang, Shiqi.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
Description:	141 p.
Notes:	Source: Dissertations Abstracts International, Volume: 80-09, Section: B.
Contained By:	Dissertations Abstracts International80-09B.
Subject:	Plant sciences. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10972966
ISBN:	9780438929937

Vacuolar Na+/H+ Antiporters in Arabidopsis thaliana: Cation Selectivity and Biological Functions.
Zhang, Shiqi.

Vacuolar Na+/H+ Antiporters in Arabidopsis thaliana: Cation Selectivity and Biological Functions. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 141 p.

Source: Dissertations Abstracts International, Volume: 80-09, Section: B.

Thesis (Ph.D.)--University of California, Davis, 2018.

This item must not be added to any third party search indexes.

Na+/H+ (NHX-type) antiporters are integral membrane transporters that catalyze the electroneutral H+-coupled transport of K+ or Na+ and are important regulators of intracellular ion homeostasis. In Arabidopsis, there are four vacuolar NHX isoforms, named NHX1 to NHX4. NHX1 and NHX2 were shown to mediate K+(Na+)/H+ exchange and regulate vacuolar pH and cellular cation homeostasis, but the function(s) of NHX3 and NHX4 remain elusive. In this dissertation, we assessed the function of the vacuolar NHX using our collection of five multi-order knockouts, four triple knockout mutants harboring only one functional NHX and one quadruple knockout lacking all four vacuolar NHX. Some triple knockouts displayed reduced growth and differential growth responses to external K+ and Na+, with K + inhibiting plant growth while Na+ restored it. We used immobilized, isolated vacuoles to measure vacuolar cation uptake. Kinetic analysis showed that NHX1, NHX2, and NHX4 mediated both K+ and Na+ transport whereas NHX3 only mediated Na+ transport. Interestingly, vacuoles isolated from the nhx1nhx2nhx3nhx4 quadruple knockout displayed Na+ transport activity that was pH independent, suggesting a presence of a Na+ conductive pathway that was independent of the NHX antiporters. The roots of the quadruple knockout displayed pronounced root skewing when grown under high K+ conditions. Pharmacological treatment targeting cortical microtubules of the roots indicated that exogenous K + could destabilize the cortical microtubules, which was supported by whole mount immune-labeling of cortical microtubules. Together, these results suggest that altered K+ homeostasis leads to an increase in the dynamics of cortical microtubules in the quadruple knockout roots. The quadruple knockout also exhibited auxin-related growth phenotypes, such as loss of apical dominance and short root growth. We evaluated auxin distribution and the localization of its transport components, the dynamics of the actin filaments and cytosolic [Ca2+] in the root of the quadruple knockout. The results showed decreased actin filament density and bundling, a reduction of PIN2 at the plasma membrane and increased steady-state cytosolic [Ca2+]cyt of the quadruple knockout roots. The study indicated that the intracellular K+ and Na+ homeostasis regulated by the vacuolar NHXs indirectly affected steady-state cytosolic calcium concentrations, affecting actin organization and PIN distributions with the concomitant alteration in auxin distribution and abnormal plant growth.

ISBN: 9780438929937Subjects--Topical Terms:

3173832
Plant sciences.

Vacuolar Na+/H+ Antiporters in Arabidopsis thaliana: Cation Selectivity and Biological Functions.
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245 1 0 $a Vacuolar Na+/H+ Antiporters in Arabidopsis thaliana: Cation Selectivity and Biological Functions.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2018
300 $a 141 p.
500 $a Source: Dissertations Abstracts International, Volume: 80-09, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
500 $a Advisor: Blumwald, Eduardo.
502 $a Thesis (Ph.D.)--University of California, Davis, 2018.
506 $a This item must not be added to any third party search indexes.
506 $a This item must not be sold to any third party vendors.
520 $a Na+/H+ (NHX-type) antiporters are integral membrane transporters that catalyze the electroneutral H+-coupled transport of K+ or Na+ and are important regulators of intracellular ion homeostasis. In Arabidopsis, there are four vacuolar NHX isoforms, named NHX1 to NHX4. NHX1 and NHX2 were shown to mediate K+(Na+)/H+ exchange and regulate vacuolar pH and cellular cation homeostasis, but the function(s) of NHX3 and NHX4 remain elusive. In this dissertation, we assessed the function of the vacuolar NHX using our collection of five multi-order knockouts, four triple knockout mutants harboring only one functional NHX and one quadruple knockout lacking all four vacuolar NHX. Some triple knockouts displayed reduced growth and differential growth responses to external K+ and Na+, with K + inhibiting plant growth while Na+ restored it. We used immobilized, isolated vacuoles to measure vacuolar cation uptake. Kinetic analysis showed that NHX1, NHX2, and NHX4 mediated both K+ and Na+ transport whereas NHX3 only mediated Na+ transport. Interestingly, vacuoles isolated from the nhx1nhx2nhx3nhx4 quadruple knockout displayed Na+ transport activity that was pH independent, suggesting a presence of a Na+ conductive pathway that was independent of the NHX antiporters. The roots of the quadruple knockout displayed pronounced root skewing when grown under high K+ conditions. Pharmacological treatment targeting cortical microtubules of the roots indicated that exogenous K + could destabilize the cortical microtubules, which was supported by whole mount immune-labeling of cortical microtubules. Together, these results suggest that altered K+ homeostasis leads to an increase in the dynamics of cortical microtubules in the quadruple knockout roots. The quadruple knockout also exhibited auxin-related growth phenotypes, such as loss of apical dominance and short root growth. We evaluated auxin distribution and the localization of its transport components, the dynamics of the actin filaments and cytosolic [Ca2+] in the root of the quadruple knockout. The results showed decreased actin filament density and bundling, a reduction of PIN2 at the plasma membrane and increased steady-state cytosolic [Ca2+]cyt of the quadruple knockout roots. The study indicated that the intracellular K+ and Na+ homeostasis regulated by the vacuolar NHXs indirectly affected steady-state cytosolic calcium concentrations, affecting actin organization and PIN distributions with the concomitant alteration in auxin distribution and abnormal plant growth.
590 $a School code: 0029.
650 4 $a Plant sciences. $3 3173832
690 $a 0479
710 2 $a University of California, Davis. $b Plant Biology. $3 1676788
773 0 $t Dissertations Abstracts International $g 80-09B.
790 $a 0029
791 $a Ph.D.
792 $a 2018
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10972966