No abstract

Thionins are small cysteine-containing, amphipathic plant proteins found in seeds and vegetative tissues of a number of plant genera. Many of them have been shown to be toxic to microorganisms such as fungi, yeast, and bacteria and also to mammalian cells. It has been suggested that thionins are present in seeds to protect them, and the germinating seedling, from attack by phytopathogenic microorganisms, but the mechanism by which they kill cells remains unclear. Using electrophysiological measurements, we have shown that ␤-purothionin from wheat flour can form cation-selective ion channels in artificial lipid bilayer membranes and in the plasmalemma of rat hippocampal neurons. We suggest that the generalized toxicity of thionins is due to their ability to generate ion channels in cell membranes, resulting in the dissipation of ion concentration gradients essential for the maintenance of cellular homeostasis.

Salt tolerance in hexaploid wheat (Triticum aestivum L.) may be determined by the D genome. Variation in salt tolerance of wild populations of Triticum tauschii (Coss.) Schmal. (donor of the D genome) was surveyed, with the aim of improving the salt tolerance of modern hexaploid wheat. A collection of 415 T. tauschii accessions was screened for Na+ concentration in the most recent fully expanded leaf, as an indicator of salt tolerance. Experiments were conducted under greenhouse conditions using gravel culture and nutrient solutions with ISO mol m−3 NaCl and 10 mol m−3 Ca2+. A subsequent growth experiment measured the relative salt tolerance of ten accessions of T. tauschii selected for high and low leaf Na+ concentrations. Salt tolerance was measured as relative biomass under saline as compared with control conditions. Two accessions were highly salt tolerant and two were highly salt sensitive. Two wheat cultivars of known salt tolerance were also tested as standards: salttolerant T. aestivum cv. Kharchia and salt‐sensitive T. turgidum L. cv. Modoc. The salt tolerance of the two most tolerant T. tauschii accessions exceeded that of the salt‐tolerant wheat standard. The salt sensitivity of the two most sensitive T. tauschii accessions equaled that of the salt‐sensitive wheat standard. Leaf Na+ concentrations in the screening and growth experiments were negatively correlated with the relative biomass in the growth experiment. This screening has identified highly salt‐tolerant T. tauschii accessions that may be useful for improving the salt tolerance of bread wheat.