EVIDENCE OF CHANGES IN CHROMOSOME MORPHOLOGY IN ROOT-TIPS OF NICOTIANA-TABACUM-L CV SAMSUN AFTER INFECTION WITH TOBACCO MOSAIC-VIRUS

When the karyotype of Nicotiana tabacum L. cv. 'Samsun' was examined i n 60 root tips in each case of three plants prior to.inoculation with tobacco mosaic virus and 26 and 34 d post infectionem (p.i.), the numb er of chromosomes (2n = 48) and the ratio of six nucleoli to six satel lites remained the same, but there were changes in the morphology of s everal chromosomes after virus infection of the plants. The satellites of the two largest satellite-bearing chromosomes had doubled in size, the long arms of chromosomes 37 and 38 had significantly shortened, a nd so had the short arms of chromosome 43. Also, the total length of t he chromosome set was reduced from 114.50 mum (non-inf.) to 106.50 mum (inf.), and the indices of proportion (Gi) and symmetry (Si) had chan ged. The changes in chromatin are interpreted in connection with telom eres and stress effects. Virus infection was assessed in the above- an d below-ground plant parts primarily by immuno-assay (DAS-ELISA) and b y the occurrence of typical TMV inclusion bodies. There was a gradient in virus content in the plant (26 d p.i.), being highest in the basal leaves, less in the plant apex, and least in root tips (7.88, 3.46 an d 1.54 mg TMV/g tissue, respectively). A novel comparison of virus con tent and inclusion bodies showed that despite the difference in TMV ti tre, the frequency of inclusion bodies in cells of root tips and leaf hairs was comparable.