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On the Understanding of Sodium Trans...

Hamam, Ahmed.

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On the Understanding of Sodium Transport and Its Role in Salinity Stress in Plants.

Record Type:	Electronic resources : Monograph/item
Title/Author:	On the Understanding of Sodium Transport and Its Role in Salinity Stress in Plants./
Author:	Hamam, Ahmed.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
Description:	146 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-01, Section: B.
Contained By:	Dissertations Abstracts International82-01B.
Subject:	Plant sciences. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27832618
ISBN:	9798662392939

On the Understanding of Sodium Transport and Its Role in Salinity Stress in Plants.
Hamam, Ahmed.

On the Understanding of Sodium Transport and Its Role in Salinity Stress in Plants. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 146 p.

Source: Dissertations Abstracts International, Volume: 82-01, Section: B.

Thesis (Ph.D.)--University of Toronto (Canada), 2020.

This item must not be sold to any third party vendors.

Soil salinity is a major threat to global agriculture, affecting >900 million hectares of land. Sodium chloride is the most soluble and widespread salt on earth, and at high cytosolic concentrations, is considered toxic. For decades, researchers have been investigating the pathways of Na+ transport and its distribution in plants under salinity stress, especially at the point of contact, the root surface, but the underlying mechanisms remain poorly resolved. According to the current proposed model, Na+ enters root cells passively (i.e. down its electrochemical gradient), via membrane channels, at very high rates and is then actively pumped out of the cytosol at nearly the same rate. This model of rapid Na+ cycling has recently been called into question, as inexplicable cellular energetics, flawed methodologies, conflicting results, and a lack of in-planta demonstrations all plague the model. The present work addresses these fundamental issues by systematically comparing radiotracer measurements and electrophysiological recordings, in conjunction with various nutritional profiles, inhibitory assays, mutant analyses, and genetic characterizations in the model systems barley (Hordeum vulgare), rice (Oryza sativa), and Arabidopsis thaliana. Efflux analysis showed the first physiological evidence of differential unidirectional Na+ efflux from distal root and bulk root zones under steady-state conditions, validating the physiological role of the Na+/H+ antiporter (SOS1) in Na+ efflux, but lack of significant involvement in rapid Na+ cycling based on known expression patterns. Electrophysiological recordings and radiotracer measurements indicated that Na+ influx is modest in nature and saturates well below any toxic concentration of Na+, in stark contrast with what is reported in the literature in support of the standing model. Influx analysis also revealed considerable plasticity in Na+ transport under salinity stress in response to nutritional changes, but only by breaking with conventional protocols. These findings provide clear evidence that the current model of rapid Na+ cycling is invalid and in need of significant reevaluation. It is concluded that most of the reported Na+ fluxes under salinity stress are a gross overestimation of symplastic flow and are more likely to be predominately apoplastic in nature.

ISBN: 9798662392939Subjects--Topical Terms:

3173832
Plant sciences.
Subjects--Index Terms:

Soil salinity

On the Understanding of Sodium Transport and Its Role in Salinity Stress in Plants.
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245 1 0 $a On the Understanding of Sodium Transport and Its Role in Salinity Stress in Plants.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2020
300 $a 146 p.
500 $a Source: Dissertations Abstracts International, Volume: 82-01, Section: B.
500 $a Advisor: Kronzucker, Herbert J.
502 $a Thesis (Ph.D.)--University of Toronto (Canada), 2020.
506 $a This item must not be sold to any third party vendors.
520 $a Soil salinity is a major threat to global agriculture, affecting >900 million hectares of land. Sodium chloride is the most soluble and widespread salt on earth, and at high cytosolic concentrations, is considered toxic. For decades, researchers have been investigating the pathways of Na+ transport and its distribution in plants under salinity stress, especially at the point of contact, the root surface, but the underlying mechanisms remain poorly resolved. According to the current proposed model, Na+ enters root cells passively (i.e. down its electrochemical gradient), via membrane channels, at very high rates and is then actively pumped out of the cytosol at nearly the same rate. This model of rapid Na+ cycling has recently been called into question, as inexplicable cellular energetics, flawed methodologies, conflicting results, and a lack of in-planta demonstrations all plague the model. The present work addresses these fundamental issues by systematically comparing radiotracer measurements and electrophysiological recordings, in conjunction with various nutritional profiles, inhibitory assays, mutant analyses, and genetic characterizations in the model systems barley (Hordeum vulgare), rice (Oryza sativa), and Arabidopsis thaliana. Efflux analysis showed the first physiological evidence of differential unidirectional Na+ efflux from distal root and bulk root zones under steady-state conditions, validating the physiological role of the Na+/H+ antiporter (SOS1) in Na+ efflux, but lack of significant involvement in rapid Na+ cycling based on known expression patterns. Electrophysiological recordings and radiotracer measurements indicated that Na+ influx is modest in nature and saturates well below any toxic concentration of Na+, in stark contrast with what is reported in the literature in support of the standing model. Influx analysis also revealed considerable plasticity in Na+ transport under salinity stress in response to nutritional changes, but only by breaking with conventional protocols. These findings provide clear evidence that the current model of rapid Na+ cycling is invalid and in need of significant reevaluation. It is concluded that most of the reported Na+ fluxes under salinity stress are a gross overestimation of symplastic flow and are more likely to be predominately apoplastic in nature.
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