ABOUT CYTOGENETIC MECHANISM OF CHEMICAL MUTAGENESIS - Ecological Consequences of Increasing Crop Productivity - page 260

24.1 INTRODUCTION
24.1.1 A SUMMARY ABOUT HISTORY OF CYTOGENETIC RESEARCH
STUDIES OF CHEMICAL MUTAGENESIS
Chemical mutagenesis was discovered in the 1940s of the twentieth century [1-3].
The scientists of many countries began to actively study the cytogenetic effects of
mutagens in meristem of growing tissues of plants. There was the openly delayed and
not delayed effect of mutagens and fundamental distinction of radiation and chemical
mutagenesis on cytological level (see e.g. reviews 4,5). Aberrations in аnа- and telo-
phases in plants were studied [3-5].
Many research studies were carried out on plants of Crepis capillaris L. This spe-
cies has three pairs of the distinguishable chromosomes. Else until the discovery of
the chemical mutagenesis, Navashin [6] investigated the karyology of genus of Crepis.
Chemical mutagens have the delayed effect on cellular level, that is, they cause
damages of chromosomes only during the synthesis of DNA. After the termination of
DNA synthesis—in the postsynthetic phase of G 2 and before its beginning—in phase
of G 1 , the chromosomes are not damaged regardless of the presence of chemical mu-
tagens [4, 5]. A basic question consists in determination of mechanism of chemical
mutagenesis on cellular level.
In the USSR, the study of mechanisms of chemical mutagenesis on cytogenetic
level were performed in the laboratory of N.P. Dubinin with coworkers and by teams
led by B.N. Sidorov and N.N. Sokolov.
Dubinin et al. (see review [7]) studied the cytogenetic effects of ionizing radiation,
chemical compounds, in particular, of the alkylating agents. This group published a
large number of papers and several monographs. N.P. Dubinin formulated the idea of
the mechanism of the chemical mutagen effect: mutagens induce potential changes in
DNA of chromosomes at all stages of the mitotic cycle, which come to light during a
number of cell generations. He called it “chain process” in mutagenesis [8].
Sidorov and Sokolov [9, 10] had another point of view. In detail, their experiments
are described in the following section. These authors analyzed the rearrangements of
chromosomes in the plantlets of C. capillaris , that is, on the asynchronous populations
of cells with regard to phases of mitotic cycle—G 1 , S, and G 2 .
24.2 AIM OF THE STUDY
In our work described later, we used a synchronous object, namely dry seeds of C.
capillaris , whose bioblasts were supposed to be in the stage G 1 . Effect of the chemical
mutagen phosphemid was analyzed in comparison with the effect of X-rays. Alkyl-
ating agent phosphemidum (synonym phosphemid, phosphazin) is di-(etilene imid)-
pyrimidyl-2-amidophosphoric acid. This compound is interesting by the fact, that it
contains two ethylene imine groups and pyrimidine [11, 12]. We were studying the
rearrangements of chromosomes in metaphases of plantlets of C. capillaris (L.).
24.3 MATERIALS AND METHODOLOGY
In experiments with phosphemid, air-dried seeds of C. capillaris of yield of 1967 were
analyzed in 1968: in April (8 months of storage after harvest), June (10 months of