Salt tolerance in the halophyte Suaeda maritima : some properties of malate dehydrogenase

Abstract

Malate dehydrogenase activity in a high speed supernatant fraction prepared from homogenates of the shoots of the halophyte Suaeda maritima was separated into two fractions by gel filtration. Sodium chloride stimulated the activity of the larger molecular mass form of the enzyme to a greater extent than that of the smaller molecular mass form : the latter constituted the bulk of the activity. The degree of stimulation by sodium chloride increased with increasing substrate concentrations. Differences between the properties of the enzymes isolated from plants grown with and without sodium chloride are described. The results obtained with the halophyte enzyme were very similar to those obtained with the glycophyte Pisum sativum . Maximum activation of enzyme activity was obtained with a salt concentration of 50 mol m -3 in both species and at higher concentrations activity was inhibited. The results are discussed in relation to the mechanism of salt tolerance in halophytes.