Physiological and biochemical response of Phoenix dactylifera L. Hayani cv. embryogenic callus and somatic embryos to salt stress under in vitro conditions

Abstract

Salinity stress as a major abiotic stress has influenced more than 6% of the world land which isincreasing daily due to climate changes. The effect of salinity on callus regeneration and organogenesis of datepalm was tested under in vitro conditions. This study was conducted to investigate the effect of salt stress oncallus proliferation, somatic embryo formation of ‘Hayani’ date palm in vitro. The embryogenic callus wassubjected to MS medium with BA at 0.05 mg/l and NAA at 0.1 mg/l supplied with different sodium chloride(NaCl) concentrations (0, 500, 1000, 1500 and 2000 ppm) for 2 subcultures. Salinity affects severalphysiological and biochemical processes. The investigated parameters include embryogenic callus growth,differentiation to form somatic embryos, fresh weight of both callus and embryos, biochemical analysis such astotal carbohydrates, proline, protein content and minerals in embryogenic callus and somatic embryos. Lowlevels of abiotic stress factors can induce favorable responses in the growth and differentiation. However, highlevels are detrimental resulting in reduced growth and some cell death. The callus fresh weight and the numberof embryos were enhanced by adding 500 and 1000 ppm NaCl to the proliferation medium; higher saltconcentrations affected the callus regeneration negatively, where at 2000 ppm NaCl the less somatic embryoswere formed. High concentrations of NaCl (1500 and 2000 ppm) decreased total soluble carbohydrates in bothembryogenic callus and somatic embryos, proline content increased gradually as the external concentration ofNaCl increased and the protein content decreased in both embryogenic callus and somatic embryos with theincrease of NaCl concentration in culture media to 2000 ppm. Salinity inhibits water uptake and increases theconcentration of toxic ions such as Na+and reduced the K+ content. Tissue culture with the use of this techniquewould allow selection for salt tolerance in the date palm. In fact, somatic embryos subjected to 500 and 1000ppm NaCl concentrations were successfully regenerated into plantlets.