Effects of Cryogenic Treatment on Plantlet Production from Frozen and Unfrozen Date Palm Callus

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Abstract
Embryogenic date palm (Phoenix dactylifera L. var. Medjool) callus cultures were treated with a cryoprotective mixture of polyethylene glycol (Carbowax 6000), glucose, and dimethylsulfoxide (10%/8%/10%, w/v); treated with the mixture, frozen to −196°C, and then thawed; or left untreated. Growth subsequent to treatment was measured as fresh weight increase and as the number of embryos produced during 18 weeks of culture. The growth of calli that were frozen and thawed, compared to the other treatments, was greatly inhibited during the first 9 weeks of culture. This inhibition disappeared in subcultured tissue. In all treatments, cultures initiated plantlets after 9 weeks. Enzyme polymorphism, for five gene-associated enzyme systems including alcohol dehydrogenase, esterase, peroxidase, phosphoglucomutase, and phosphoglucoisomerase, was analyzed in leaves of regenerated plantlets by using starch gel electrophoresis for separation. Isozyme patterns were similar for all treatments.