Salinity effect on bioelectric activity, growth, Na+ accumulation and chlorophyll fluorescence of maize leaves: a comparative survey and prospects for screening

Changes in the bioelectric activity of maize leaves caused by a single light pulse (6 s; 70 μmol m-2 s-1) were used to compare the effects of NaCl treatment (20-200 mM) on plant growth, Na+ accumulation in leaves, chlorophyll fluorescence and pigment composition. Bioelectric responses seemed to be the most sensitive indicator of NaCl effects. Even the weakest salt treatment (20 mM) caused a statistically significant decrease (about 40%) in the amplitude of the bioelectric response. The higher the NaCl concentration, the smaller was the amplitude. Over the full concentration range, the characteristic time of response increased from about 30 to 60 sec, indicating that the rate of bioelectric changes was slowed by increasing salinity. Other reliable characteristics were found to be the fluorescence yield and quenching coefficients. The F(v)/F(m) ratio was not significantly affected by NaCl treatment. Changes in growth rate, biomass or pigment composition were either insensitive, or showed a plateau over a wide range of NaCl concentrations, and were inappropriate for screening. A possible link between bioelectric and fluorescence characteristics is discussed. We conclude that leaf bioelectric activity can be used together with, or instead of, chlorophyll fluorescence measurements, to screen genotypes for salt tolerance.