Recovery and characterization of amino acid analog‐resistant carrot and tobacco suspension‐cultured cells after cryostorage for over 10 years

Several Daucus carota (carrot) and Nicotiana tabacum (tobacco) cell lines that had been selected as resistant to Pro, Trp, Lys and Met analogs were thawed after over 10 years of cryostorage in liquid nitrogen. Some of these cell lines had been cloned. Viable cells were recovered in all cases, and growing lines were recovered from the carrot lines when placed either on feeder plates or directly into liquid medium. Some tobacco cultures were recovered only in liquid medium, but two Trp analog‐resistant cloned lines could not be recovered after several attempts. Generally the cryopreserved lines retained the original resistance and corresponding free amino acid levels while the same lines maintained as callus with monthly transfers for the same period often lost the resistance. Our study shows that carrot and some, but not all, tobacco cultured cell lines can be cryopreserved for over 10 years and still be recovered with their original characteristics.