High Salinity Tolerance in the stl2 Mutation of Ceratopteris richardii is Associated with Enhanced K+ Influx and Loss

Authors

Thomas R. Warne, University of Tennessee - Knoxville
Leslie G. Hickok, University of Tennessee - Knoxville
Thomas B. Kinraide, Agricultural Research Service
Dale L. Vogelien, Kennesaw State UniversityFollow

Department

Molecular and Cellular Biology

Document Type

Article

Publication Date

1-1996

Abstract

The roles of K⁺ uptake and loss in the salinity response of the wild type and the salt-tolerant mutant stl2 of Ceratopteris richardii were studied by measuring Rb⁺ influx and loss and the effects of Na⁺, Mg²⁺, Ca²⁺ and K⁺-transport inhibitors. In addition, electrophysiological responses were measured for both K⁺ and Rb⁺ and for the effects of Na⁺ and NH₄+ on subsequent K⁺-induced depolarizations. stl2 had a 26–40% higher uptake rate for Rb⁺ than the wild type at 0.5–10 mol m^-3 RbCl. Similarly, membrane depolarizations induced by both RbCl and KCl were consistently greater in stl2. In the presence of 0–180 mol m^-3 NaCl, stl2 maintained a consistently greater Rb⁺ influx than the wild type. stl2 retained a greater capacity for subsequent KCl-induced depolarization following exposure to NaCl. Five mol m^-3 Mg²⁺ decreased Rb⁺ uptake in stl2; however, additional Mg²⁺ up to 40 mol m^-3 did not affect Rb⁺ uptake further. Ca²⁺ supplementation resulted in a very minor decrease of Rb⁺ uptake that was similar in the two genotypes. Tetraethylammonium chloride and CsCl gave similar inhibition of Rb⁺ uptake in both genotypes, but NH₄Cl gave substantially greater inhibition in the wild type than in stl2. NH₄Cl resulted in a greater membrane depolarization in the wild type and the capacity for subsequent depolarization by KCl was markedly reduced. stl2 exhibited a higher Independent loss of Rb⁺ than the wild type, but, in the absence of external K⁺, loss of Rb⁺ was equivalent in the two genotypes. Since constitutive K⁺ contents are nearly identical, we conclude that high K⁺ influx and loss exact a metabolic cost that is reflected in the inhibition of gametophytic growth. Growth inhibition can be alleviated by reduced supplemental K⁺ or by treatments that slightly reduce K⁺ influx, such as moderate concentrations of Na⁺ or Mg²⁺. We propose that high throughput of K⁺ allows maintenance of cytosolic K⁺ under salt stress and that a high uptake rate for K⁺ results in a reduced capacity for the entrance and accumulation of alternative cations such as Na⁺ in the cytosol.

Journal Title

Plant, Cell & Environment

Journal ISSN

0140-7791

Volume

19

Issue

1

First Page

24

Last Page

32

Digital Object Identifier (DOI)

10.1111/j.1365-3040.1996.tb00223.x