Low concentrations of BAP and high rate of subcultures improve the establishment and multiplication of somatic embryos in date palm suspension cultures by limiting oxidative browning associated with high levels of total phenols and peroxidase activities

Taking into account the recalcitrance of date palm (Phoenix dactylifera L.) to tissue culture, establishment and proliferation of embryogenic suspension cultures in two date palm cultivars, namely Boufeggouss (BFG) and Bouskri (BSK) was implemented using liquid medium with different concentrations of the 6-benzylaminopurine (BAP) (0.3, 0.4, 0.5 mg/l) and various subculturing times (7 days, 15 days and 20 days). Total phenols and peroxidase activities have been determined and oxidative browning process checked in different cultures. The liquid medium with 0.3 mg/l BAP allowed cell suspension cultures to produce the greater globular embryos and the highest number of somatic embryos in comparison with the other treatment for BFG and BSK date palm cultivars. The low rate of culture transfers (every 15 or 20 days) tended to increase the phenolic contents and peroxidase activities in plant tissue leading to an enhancement of tissues/cells browning and then a decrease in the proliferation of embryogenic cells. The transfer of cultures on fresh medium every 7 days allowed a substantial reduction of tissue/cell oxidative browning, which is related to reduction of phenolic compounds and decrease in peroxidase activities with a resultant increase in the proliferation of embryogenic cells. This result suggests that oxidative browning is mainly peroxidase-based in date palm suspension cultures. Relationships between low concentrations of BAP as cytokinin, high growth of embryogenic cells, low contents of phenolics, decrease of peroxidase activities and oxidative browning process, are discussed, in order to optimize date palm multiplication through somatic embryogenesis and solve recalcitrance of many date palm cultivars to tissue culture.

► Low concentrations of BAP improved the multiplication of somatic embryos in date palm suspension cultures.
► High rate of subcultures allowed a reduction in browning and phenolics with a decrease in peroxidase.