Factors influencing cucumber (Cucumis sativus L.) somatic embryogenesis. I. The crucial role of pH and nitrogen in suspension culture

Abstract

A method of obtaining and the characteristics of an embryogenic stabilised cucumber (Cucumis sativus L.) suspension culture which has many similarities to the carrot model are presented. The Specific Type I cells and proembryogenic mass were present in such a suspension. The maintenance of the proembryogenic stage took place in medium containing 2,4-D as the sole growth regulator, subsequent stages of embryogenesis occurred in hormone-free medium. Embryonic structures were also observed in medium with auxin in the late stages of growth, probably due to the depletion of 2,4-D in the medium during subculture. The choice of the proper inorganic nitrogen sources and the maintenance of correct proportions between them had a significant effect on the formation of these structures. We have shown that the pH of the medium with an embryogenic culture became stabilized regardless of the initial pH value and depended on the medium composition. The inoculum used for the initiation of subsequent subcultures of the stable suspension culture was 1 part tissue to 300 parts medium and was small in comparison to the systems described for the cucumber so far. From 1 ml of basic suspension 7 embryos were obtained on medium without growth regulators 10 days after inoculation, and this amount increased to 21 after 3 weeks. From 3.2% of the somatic embryos it was posible to regenerate plants. The high yield and synchronisation of the process and the development of embryos without passing through callus tissue create the possibility of using this system for molecular investigations and in the technology of somatic seed production.