PHYSIOLOGICAL AND BIOCHEMICAL RESPONSE OF Phoenix dactylifera L. HAYANI cv. EMBRYOGENIC CALLUS AND SOMATIC EMBRYOS TO SALT STRESS UNDER IN VITRO CONDITIONS

Rezumat

Salinity stress as a major abiotic stress has influenced more than 6% of the world land which is
increasing daily due to climate changes. The effect of salinity on callus regeneration and organogenesis of date
palm was tested under in vitro conditions. This study was conducted to investigate the effect of salt stress on
callus proliferation, somatic embryo formation of ‘Hayani’ date palm in vitro. The embryogenic callus was
subjected 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 several
physiological 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 as
total carbohydrates, proline, protein content and minerals in embryogenic callus and somatic embryos. Low
levels of abiotic stress factors can induce favorable responses in the growth and differentiation. However, high
levels are detrimental resulting in reduced growth and some cell death. The callus fresh weight and the number
of embryos were enhanced by adding 500 and 1000 ppm NaCl to the proliferation medium; higher salt
concentrations affected the callus regeneration negatively, where at 2000 ppm NaCl the less somatic embryos
were formed. High concentrations of NaCl (1500 and 2000 ppm) decreased total soluble carbohydrates in both
embryogenic callus and somatic embryos, proline content increased gradually as the external concentration of
NaCl increased and the protein content decreased in both embryogenic callus and somatic embryos with the
increase of NaCl concentration in culture media to 2000 ppm. Salinity inhibits water uptake and increases the
concentration of toxic ions such as Na+
and reduced the K+ content. Tissue culture with the use of this technique
would allow selection for salt tolerance in the date palm. In fact, somatic embryos subjected to 500 and 1000
ppm NaCl concentrations were successfully regenerated into plantlets.