FACTORS INFLUENCING CUCUMBER (CUCUMIS-SATIVUS L) SOMATIC EMBRYOGENESIS .1. THE CRUCIAL ROLE OF PH AND NITROGEN IN SUSPENSION-CULTURE

A method of obtaining and the characteristics of an embryogenic stabil ised cucumber (Cucumis sativus L.) suspension culture which has many s imilarities to the carrot model are presented. The Specific Type I cel ls and proembryogenic mass were present in such a suspension. The main tenance of the proembryogenic stage took place in medium containing 2, 4-D as the sole growth regulator, subsequent stages of embryogenesis o ccurred in hormone free medium. Embryonic structures were also observe d in medium with auxin in the late stages of growth, probably due to t he depletion of 2,4-D in the medium during subculture. The choice of t he proper inorganic nitrogen sources and the maintenance of correct pr oportions between them had a significant effect on the formation of th ese structures. We have shown that the pH of the medium with an embryo genic culture became stabilized regardless of the initial pH value and depended on the medium composition. The inoculum used for the initiat ion of subsequent subcultures of the stable suspension culture was 1 p art tissue to 300 parts medium and was small in comparison to the syst ems described for the cucumber so far. From 1 mi of basic suspension 7 embryos were obtained on medium without growth regulators 10 days aft er inoculation, and this amount increased to 21 after 3 weeks. From 3. 2% of the somatic embryos it was posible to regenerate plants. The hig h yield and synchronisation of the process and the development of embr yos without passing through callus tissue create the possibility of us ing this system for molecular investigations and in the technology of somatic seed production.