Search

The object of this investigation was the mutagenic effect of kinetin (6-phurphuryl-aminopurine) on chromosomes of Crepis capillaris L. Dry seeds were soaked in the 0.05% kinetin solution for 4, 6 and 8 hours before the irradiation with X-rays. It is observed that soaking of dry seeds in kinetin solution stimulates the appearance of chromatid aberrations for almost two hours earlier, than in the control (soaking seeds in water). A regular increase of the chromatid-type rearrangements with increasing the duration of soaking in the kinetin solution was observed (3.3%, 16-20% and almost 50% at 4 hours; 6 hours' and 8 hours' soaking respectively). This increase is indicative for the effect of kinetin on the processes taking place in the cell before the irradiation. Apparently kinetin stimulates the onset of the stage S for a certain proportion of cells, and thus at the moment of irradiation the cell population is at the asynchronous state. A considerable radioprotective effect of kinetin was observed in all the variants of the experiment, which is not associated with the capacity of stimulating the initiation of chromatid aberrations inherent in kinetin. Kinetin alone (without irradiation) exerts no mutagenic effect on the cells of Crepis capillaris.

Seedlings of Crepis capillaris were irradiated after pulse-labelling with tritiated thymidine ([3-H]TdR), and both chromosomal aberrations and presence of silver grains were recorded in the same metaphase cells at various intervals throughout the whole mitotic cycle. The following results were obtained: (a) irradiated roots were homogeneous with respect to the number of aberrations, and heterogenous with respect to labelling index (LI); (b) time--effect curves for labelled (L) and unlabelled (U) cells showed no significant difference from one another; (c) no significant quantitative difference of aberration spectra produced in S and G2 stages was found. These results support the view that the major factor which determines both quantitative and qualitative variation in the production of chromosomal aberrations by radiation is the time lapse between irradiation and fixation rather than relation of the time of irradiation to the time of DNA synthesis. In addition, it was found that labelling with [3-H]TdR modifies the effect of radiation on chromosomes.

Air-dry Crepis capillaris seeds, soaked for 14 and 20 hours, were dried to the moisture content of 1,1% with the following gamma-irradiation at a dose of 1500 r. Irradiated seeds were stored in the state of identical moisture for 38 days. The drying of three groups of seeds to moisture content of 1,1% provided their identical initial radiosensitivity. In the course of the storage mutability of treated seeds significantly increased as compared with the yield of mutations in non-stored seeds, and revealed undulating kinetics that involved all types of arising chromosome and chromatid rearrangements. The character of undulating kinetics is due to a correlation between functional state of nucleus (early G1, late G1, S) and water content in seeds.

When seeds of Crepis capillaris were germinated in solutions of Cu(NO3)2 (at 0.55-10(-5) M and 1.1-10(-5) M concentrations) the frequency of structural chromosome mutations induced by gamma-rays (137Cs) at 200 and 400 r doses was higher as compared to that induced in the absence of copper ions.

A distribution of chromosome X-rays induced aberrations was studied in 2n and 4n root cells of Crepis capillaris at different stages of the mitotic cycle. Participation of various chromosomes in aberrations was found to be different from theoretically expected one found from the chromosome length. The chromosome A was characterized by excession of intrachromosome aberrations (terminal deletions, isolocuses, duplications and rings). The chromosome D very often took part in the formation of rings. The chromosome C was characterized by an excession of interchromosome aberrations and the lack of intrachromosome ones. The data obtained support the model of interphase nucleus proposed by Wagenaar. The frequency of exchanges of homologues in 2n and 4n cells well correlated with theoretically expected. The inhibition of mitosis increased the exchanges of homologues. In 2n and 4n cells asymmetrical translocations predominated over symmetrical ones.

The experiments were carried out on Lactuca sativa seeds exposed for 20, 66, 123 and 308 days in a biostack also containing physical detectors of heavy charged particles. The purpose of the experiments was to measure the yield of aberrant cells and its dependence on the exposure time and the site where particles hit the object. The cytogenetic examination demonstrated a significant difference between the seeds that were or were not hit by heavy charged particles. This is indicative of a significant contribution of galactic cosmic radiation to the radiobiological effect. The yield of aberrant cells as a function of the localization of heavy charged particles in the seed was established. The most sensitive target was the root meristem.

In radicle meristem cells of germinating seeds of the pea (Pisum sativum L) before the onset of replicative synthesis of DNA, irradiation with 2-3 krad of gamma-rays induced the incorporation of 3H-thymidine (3H-TdR). Maximum isotope incorporation was noted during the first 2 hours after irradiation. Higher doses of radiation suppressed 3H-TdR incorporation. It was not seen after gamma-irradiation of air-dried seeds, nor after fast-neutron irradiation. The replication inhibitors hydroxyurea and 5-aminouracil had no effect on the gamma-induced incorporation of 3H-TdR, Whereas caffeine and acriflavine inhibited it to some extent. It is suggested that the gamma-radiation-induced incorporation of 3H-TdR in meristem cells during the pre-replicative period may be connected with repair phenomena.