[Cytogenetic effect of temperature on the sunflower varieties].

The influence of increased temperature on the intensity of fission and level of chromosome aberrations (ChA) in root meristeme cells of two lines of sunflower seedlings was studied. Within the first hour of seed germination, the temperature of 40 degrees C reduced proliferation activity of root meristeme cells line 3629 for almost the next 15 h of growth. Heat stress (HS) blocks the beginning of cell fission in the plastome mutant en-chlorina-5. However, subsequent by mitosis activity was seen to increase. The influence of HS on the ChA level is ambiguous: the effect depends on the duration of warm-up influence and the used sunflower lines. So, ChA level does not change inbred line 3629 even after 6 h HS. In mutant en-chlorina-5 the ChA level increases after 1 h HS and decreases after 3 and 6 h HS. The study of HS modification effect has shown that preliminary warm-up influence (40 degrees C for 1 h) reduces differences in reactions of cells 3629 of line on the action of different nitrosomethylurea (NMU) concentrations. Preliminary warm-up influence does not change sensitivity of en-chlorina-5 cells to NMU. The combined action of the increased temperature and NMU induce a powerful cytostatic effect.