Actual cytokinin concentrations in plant tissue as an indicator for salt resistance in cereals

Growth rates of roots and shoots of hydroponically grown plants of a salt resistant variety of barley decreased rapidly after an exposure to 65 Mm⁻³ sodium chloride. This growth rate reduction tended to be temporarily and it was accompanied by a lowered shoot to root ratio. At the same time growth reduction took place, the cytokinin concentrations in root and shoot tissue decreased rapidly too, as they were measured by an enzyme-linked immuno assay. The addition of 5·10⁻⁹ Mm⁻³ benzyladenine (BA) retarded the decreases of growth rates, shoot to root ratio and internal cytokinin concentrations. Growth rates of roots and shoot of identically grown plants of salt sensitive varieties of barley maintained their growth rates and shoot to root ratio after an exposure to NaCl for at least ten days in combination with unchanged levels of endogenous cytokinins. After ca 14 days NaCl induced severe decreases in RGR values, but not in shoot to root ratio. Addition of benzyladenine inhibited growth to some extent and enhanced the cytokinin concentration. It was concluded, that cytokinin concentrations measured directly after exposure to NaCl form a promising screening method for salt resistance. The addition of BA made salt resistance varieties behave as salt sensitive varieties.