Enhanced sensitivity to the mutagenic action of methylnitrosourea in a transgenic clone of tobacco carrying the E. coli gene ada

145 others smaller and darker in a 2 : 1 ratio; (c) 21% embryos with one or both multinucleated blastomers compared with no embryos of this type in control mice. Altogether these results suggest the usefulness of testing the same chemical in various in vivo cell systems to obtain information about different kinds of effect (nondisjunction, chromosome loss, complete disruption of meiotic and mitotic division), their kinetics and rate of induction.

71 St6tina, R., Institute of Experimental Medicine, Czechoslovak Academy of Sciences, Ole~nice v Orlichk~ch horfich (Czechoslovakia) Repair-deficient Chinese hamster cell line CHOUV-5 is unable to remove from the DNA alkali labile sites induced by methyl methanesulfonate

The repair of the DNA damage induced by methyl methanesulfonate (MMS) in normal CHO cells has two phases. During the first 3 h after the treatment of ceils about half of induced alkali labile sites (ALS) are removed from the DNA. After 3-6 h the number of ALS increases again and they are removed at a slower rate. The presence of 10 -4 M araC and 10 -2 M hydroxyurea causes an increase in ALS, 10 -3 M novobiocin decreases their number. The amount of MMS-induced ALS in the DNA of the UV-5 mutant increased during the post-treatment period, no effect of DNA repair inhibitors was observed. It seems that only some of the ALS that are repaired within the first 6 h after the treatment have toxic effects, because MMS is only 2-3 times more toxic to the UV-5 mutant than to normal CHO cells.

VI. Mutagenicity studies in plants

72 Baburek, I. 1, T. Gichner 1, j. Briza 2, j. Veleminsky 1 and G. Margison 3, i IEB CSAV, Prague, 2 IMBP CSAV, Cesk6 Budojovice

(Czechoslovakia) and 3 Paterson Institute for Cancer Research, Manchester (UK) Enhanced sensitivity to the mutagenic action of methylnitrosourea in a transgenic clone of tobacco carrying the E. coli gene ada

Transfer of the E. coli gene ada into the genome of tobacco (Nicotiana tabacum var. Xanthi) increased the resistance of in vitro cultivated cells and calluses, derived from transgenic clones, against the toxic (growth inhibiting) action of Nomethyl-N-nitrosourea (MNU) and chloroethylnitrosourea derivatives (TCNU, ACNU). However, a similar resistance was not detected against the mutagenic action of MNU. Moreover, in one transgenic clone (X3) the frequency of somatic mutations in two genes controlling synthesis of chloroplast pigments was significantly enhanced not only after the action of MNU but also after the action of the nonalkylating agent maleic hydrazide. Possible reasons for this enhanced sensitivity to the mutagenic action due to the gene transfer are discussed.

73 Bavcon, J., B. Dru~kovi~ and D. Pape~ 1, Institute of Biology, University of Ljubljana, Karlov~ka 19, 61000 Ljubljana, Slovenia and 1 Department of Botany, Faculty of Science, University of Zagreb, Roosveltov trg 6 / I l l , 41000 Zagreb, Croatia (Yugoslavia) Cytogenetic studies of seed material in a population of the Norway spruce (Picea abies (L.) Karst.) in polluted areas in Slovenia

We evaluated the damage to the genetic material of the Norway spruce (Picea abies (L.) Karst.) in 12 populations with different degrees of pollution. Indicators for the extent of damage were: ability to germinate, the mitotic index, and cytogenetic analysis. Seeds of the Norway spruce were collected at 12 sites in Slovenia and were separated into three groups in view of the type and degree of pollution. The percentages of seed germination showed significant differences between sites yet did not