Effect of calcium on root development and root ion fluxes in salinised barley seedlings

The effects of various Na/Ca ratios on root growth, development, and ion acquisition patterns were studied in hydroponic experiments with barley ( Hordeum vulgare L.) plants. In total, interactions between three different levels of salinity ( 1, 50 and 100 mM NaCl) and three different levels of Ca(2+) (0.1, 1 and 10 mM) were studied ( a full factorial experiment). Growth rate and biomass accumulation were significantly lower in salinised roots. In addition to reduction in extension growth, salinity also significantly affected plant developmental processes ( for example reduced root hair density and root thickening). Supplemental Ca(2+) significantly ameliorated those detrimental effects of salinity. Non-invasive, microelectrode ion-flux (MIFE) measurements showed that the onset of salt stress caused rapid and prolonged efflux of H(+), K(+) and NH(4)(+) from the root epidermis. This efflux could be significantly reversed, or completely prevented, by the presence of high Ca(2+) concentration in the bath solution, even after several days of salt stress. Membrane potential measurements in root epidermal cells showed that high Ca(2+) levels in the bath were able to restore ( otherwise depolarised) membrane potential back to control level ( - 120 to - 130 mV). At the same time, no significant impact of Ca(2+) on net Na(+) uptake in plant roots was found. Some limitations of the MIFE technique for study of Na(+) uptake kinetics under saline conditions, as well as possible ionic mechanisms underlying the ameliorating Ca(2+) effects on ion fluxes in roots of salt-stressed plants, are discussed.