The influence of some environmental factors on cytological and biometric parameters and chlorophyll content of Deschampsia antarctica Desv. in the maritime Antarctic

Under the environmental conditions of the Point Thomas Oasis (King George Island, the South Shetland Islands), we studied the influence of month-long artificial treatment with fresh water, salt water, and guano solution on the biometric characteristics, chlorophyll content, as well as the nuclear area of leaf parenchymal cells and nuclear DNA content, in a maritime Antarctic aboriginal plant Deschampsia antarctica. The modeled factors induced an increase in the generative shoot height and the length of the largest leaf, but did not influence the number of flowers. Treatment with guano caused an increase in the chlorophyll a and b contents, while fresh water treatment only led to some increase in chlorophyll a. Fluctuations of physiologically significant traits, such as the nuclear area and DNA content in the leaf parenchyma cells of D. antarctica, have been traced under the influence of the studied factors. Understanding of the hierarchy of influence of these factors as well as and sensitivity of plants of this species to external agents require further investigation.     

Mixoploidy in wild and cultivated species of Cruciferae capable of hybridizing with rapeseed Brassica napus

The number of chromosomes in cells of the root meristem of seedlings of wild and cultivated species of Cruciferae plants capable of hybridizing with rapeseed Brassica napus is studied. Only diploid metaphases are observed in seedlings of Brassica juncea, Diplotaxis tenuifolia, and Raphanus raphanistrum. In B. napus and B. cretica roughly 5% of the seedlings are mixoploid. Diploid cells are dominant in the mixoploids, though hypo-and hyperdiploids are also encountered. Nearly 20% of the seedlings of B. campestris and R. sativum are mixoploid, a significant fraction of which contains di-triploid chimeras. In B. nigra less than one-half of the seedlings are truly diploid, the majority of the plants being mixoploid. Seedlings containing preferentially tetraploid and triploid cells are dominant. The biological significance and possible causes of the newly discovered mixoploidy are discussed.     

Fractionation of eukaryotic DNA in a pulsed electrical field. II. Discrete DNA fragments and level of structural organization of chromatin]

The data presented confirm the possibility of enzymatic formation of discrete DNA-fragments appearing during fractionation of nuclear DNA by FIGE. Teniposide-dependent pattern of DNA-fragments as well as occurrence of protein-linked DNA breaks suggest that discrete cleavage of intact nuclear DNA is modulated by DNA topoisomerase II. The possible relationship between discrete DNA-fragments and the higher order chromatin folding are discussed.     

Antimutagenesis as organism defense system against damaging factors of endogenous and exogenous origin

Antimutagenic system is represented as the system combining all enzymatic and metabolic processes of the organism at all levels. The problem of supporting of autoantimutagenic system with antimutagenic preparations is discussed. A number of possible mechanisms of antimutagenic action of different substances are considered.