Characterization of Two Non Constitutive Hydroxycinnamic Acid Derivatives in Date Palm (Phoenix dactylifera L.) Callus in Relation with Tissue Browning

Two new phenolic compounds were isolated from date palm (Phoenix dactylifera L.) callus and have been identified to be apolar hydroxycinnamic acid derivatives (DHC3 and DHC4) by spectrophotometry, thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) separations. Their accumulation is being in relation with tissue browning that occurs during in vitro culture and is cultivar dependent. A higher accumulation of these two DHCs was observed in BSTN and BFG cultivars (`susceptibles` to browning) compared to JHL and IKL cultivars (less `susceptibles` to tissue browning). These compounds were completely degraded with 100 U mL-1 of exogenous peroxidase. Their formation doesn`t occur when enzymatic extract was added to phenolic acids demonstrating that DHC3 and DHC4 constitute a substrate and not a product of enzymes implicated in tissue browning. The possible relationship between DHC3 and DHC4 and abiotic stress leading to tissue browning which affects somatic embryogenesis in date palm is discussed.