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Title:Characterization of sodium transport at the plasma membrane of Spergularia marina
Author(s):Wickens, Linda Karolyn
Doctoral Committee Chair(s):Cheeseman, John M.
Department / Program:Plant Biology
Discipline:Biology, Botany
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Botany
Biology, Cell
Biology, Plant Physiology
Abstract:Plants vary in their whole plant strategies for managing the sodium (Na$\sp{+}$) present in their environment, but current models predict that they have a common strategy at the cellular level: exclusion from the cytoplasm. This entails either passive exclusion mediated by low plasma membrane permeability or active exclusion of passively acquired Na$\sp{+}$ which has moved down its electrochemical gradient into the cell. Whole plant studies using the halophyte Spergularia marina have demonstrated high permeability for Na$\sp{+}$ into and out of root cells and the research reported here investigates these mechanisms by directly measuring Na$\sp{+}$ transport using radiolabelled Na$\sp{+}$ and sealed plasma membrane vesicles from the roots of this species. This is the first report to characterize $\sp{22}$Na$\sp{+}$ transport using plant plasma membrane vesicles.
Fractions from discontinuous and linear gradients of sucrose that were enriched in plasma membrane vesicles were identified for use in the $\sp{22}$Na$\sp{+}$ transport studies by the orthovanadate-sensitive P-type H$\sp{+}$-ATPase activity associated with them. Both the scalar and vectoral components of the activity were found to have negligible Na$\sp{+}$-dependent modifications. Indirect Na$\sp{+}$-dependent effects were observed, suggesting that Na$\sp{+}$ could disrupt K$\sp{+}$-dependent modifications of both components of the ATPase activity. An alternative explanation of the data was that an ATP-dependent, orthovanadate-insensitive, Na$\sp{+}$-dependent transport mechanism(s) mediated vesicle acidification. Radiolabelled Na$\sp{+}$ transport studies using similar conditions failed to show the presence of ATP-dependent transport of Na$\sp{+}$; and in addition, vesicle acidification studies, as well as $\sp{22}$Na$\sp{+}$ transport studies, suggested that a Na$\sp{+}$/H$\sp{+}$ antiport mechanism was not present in the plasma membrane. Two $\Delta\mu\sb{\rm Na+}$-driven transport mechanisms were identified using efflux studies. Lineweaver-Burk analysis predicted the presence of a Na$\sp{+}$ transport mechanism with a K$\sb{\rm m}$ of 93 mM Na$\sp{+}$ and a V$\sb{\rm max}$ of 52.6 nmoles Na$\sp{+}$ $\cdot$ (mg prot $\cdot$ min)$\sp{-1}$. Studies with monensin suggested that there was a Na$\sp{+}$-dependent alkalinization of the vesicles when the $\Delta\mu\sb{\rm Na+}$ was high.
Issue Date:1991
Rights Information:Copyright 1991 Wickens, Linda Karolyn
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9211033
OCLC Identifier:(UMI)AAI9211033

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