In vitro Responses of Date Palm Cell Suspensions under Osmotic Stress Induced by Sodium, Potassium and Calcium Salts at Different Exposure Durations

In vitro cultures subjected to salt-stress have been shown to exhibit unique characteristics that are useful for identifying stress status. The objective of this study was to investigate the physiological responses of date palm, Phoenix dactylifera L. cv. Barhee, callus to salinity stress. Callus were cultured on MS medium supplemented with NaCl, KCl, or CaCl2 at 0.8 MPa (-8 bars) equivalent osmotic potential concentrations. The exposure to salt stress resulted in reduction in callus dry weight as compared to the control. Sodium chloride caused the highest reduction in dry weight followed by KCl then CaCl2. In general, callus water content decreased in response to extending exposure durations regardless of the salt type used. Increasing the exposure duration up to 6 days caused increase in proline content compared to the control. Extending the exposure duration of KCl and CaCl2 to 9 days caused reduction in proline content, due to cell death as indicated by culture browning. Exposure to NaCl initially caused increase in Na+ content but at the ninth day, significant reduction in Na+ content was observed. Increasing salt exposure duration caused significant increase in K+ content as compared to the control, up to 3 days of exposure after which the content decreased but remained higher than the control cultures. The Na+/K+ ratio was also significantly affected by the salt type and the exposure duration. This study has enhanced the understanding of the influence of salinity on physiological aspects of date palm cell cultures.