INTERTRIBAL SOMATIC HYBRIDS BETWEEN BRASSICA-NAPUS AND THLASPI-PERFOLIATUM WITH HIGH CONTENT OF THE T-PERFOLIATUM-SPECIFIC NERVONIC ACID

Protoplast fusions were performed between hypocotyl protoplasts of Bra ssica napus and mesophyll protoplasts of Thlaspi perfoliatum. The two species are members of the Lepidieae and Brassiceae tribes, respective ly, in the family of Brassicaceae. Seeds of T. perfoliatum are rich in the fatty acid C-24:1 (nervonic acid), an oil valuable for technical purposes. In the search for renewable oils to replace the mineral oils , plant breeders have been trying to develop oil crops with a high con tent of long-chain fatty acids. After fusion of B. napus protoplasts w ith non-irradiated as well as irradiated protoplasts of T. perfoliatum selection was carried out by flow cytometry and cell sorting. Of the shoots regenerated from different calli 27 were verified as hybrids or partial hybrids using the isoenzyme phosphoglucose isomerase (PGI) as a marker. Another 6 plants were identified as partial hybrids using a T. perfoliatum-specific repetitive DNA sequence. Slot blot experiment s were performed to estimate the copy number of the repetitive DNA seq uence in the parental species and in the hybrids. In T. perfoliatum th ere were approximately 10(5) copies per haploid genome, and the range in the hybrids was 1-37% of the value in T. perfoliatum. When the nucl ear DNA content of the regenerated shoots was analysed we found partia l as well as symmetric hybrids. Even though the rooting and establishm ent of hybrid shoots in the greenhouse were difficult, resulting in th e death of many plants, 19 plants were cultured to full maturity. Seed s obtained from 15 plants were analysed to determine whether they cont ained nervonic acid, and 5 of the hybrids were found to contain signif icantly greater amounts of nervonic acid than B. napus.