Biochemical responses to cadmium and lead stresses in date palm (Phoenix dactylifera L.) plants

Investigations were conducted on young date palm (Phoenix dactylifera L.) plants derived from tissue culture to evaluate their biochemical responses to cadmium and lead treatments through irrigation water. Changes in date palm metabolisms were observed as a response to heavy metals accumulation, the reductions in photosynthetic pigments as chlorophyll and carotenoides were obvious after 180 days of treatments, compared with the increase in anthocyanin pigments which was twofold more than control plants. It is noteworthy, that Cd and Pb treatments induced a significant decrease in chlorophyll stability index (CSI) to 66.97 and 58.79%, in Cd (9 mg/kg) and P (276 mg/kg), respectively. Stressed P. dactylifera plants tend to accumulate more carbohydrates, free amino acid and proline in their leaves as consequences of heavy metal treatments. Interestingly, the level of total soluble proteins was found to be less, up to twofold, than those in non-stressed plants. An excessive production of reactive oxygen species (ROS) was generated by P. dactylifera plants exposed to Cd and Pb, an increase in hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulations was observed in stressed plants, with a significant reduction in membrane stability index (MSI), the MSI was 78.8% in nonstressed plants and decreased significantly to 66.17 and 60.90%, under Cd and Pb at high concentrations, respectively. The activity of antioxidant enzyme peroxidase and total phenolic compounds were enhanced under Cd and Pb treatments. The present study supports the potential toxic effect of Cd and Pb on date palm by hampering metabolism and interfering with biological functions