H. Nicoloff

Sister chromatid exchanges in barley.

SummaryA mean frequency of 20.6 sister chromatid exchanges (SCEs) per cell has been observed in a reconstructed karyotype of Hordeum vulgare by application of the FPG technique after unifilar incorporation of BrdU into chromosomes. The involvement in SCEs of the 48 segments into which the chromosome set had been subdivided was, with a single deviation, length proportional and independent of the segments heterochromatin content. Asymmetric bands, indicative of an uneven distribution of adenine and thymidine between the DNA strands in adenine (A)-thymidine (T) rich chromosome regions, could not be detected after incubation of the cells in BrdU for one cycle of DNA replication.

On the induction of chromosome structural changes by hydroxylamine in Vicia faba

Abstract Primary roots of a new karyotype of Vicia faba with all chromosomes inter-distinguishable have been used to study the induction by hydroxylamine hydrochloride (HA) of chromatid aberrations and their intrachromosomal distribution. HA induced both chromatid intra- and interchanges of the delayed type. The effectiveness of HA increased with increasing temperature and was dependent on the pH during treatment (more aberrations at pH 7.5 as compared with 4.8). The frequency of incomplete reunion was markedly higher after HA treatment than after treatment with maleic hydrazide (MH) or ethanol. In combined treatments, HA reduced the reunion involvement in HA-induced aberrations of certain chromosome segments was found and compared with distribution patterns of chromatid aberrations after treatment with MH and ethanol. Data and hypotheses concerning possible modes of action of HA eventually resulting in chromosome structural changes are discussed. It is concluded that alterations of the cytosine moiety in chromosomal DNA are not responsible for chromosomal damage induced by HA.

Mutations in rDNA. 1. Dependence of chromosome mutation induction on positions and activity of nucleolus organizer regions.

SummaryStudies on chromatid aberration induction in NORs of standard and reconstructed karyotypes, as well as in the single translocation lines of barley, indicate a correlation between synthetic activity (transcription) of rDNA and frequency of chromosome mutations induced by HU. Experimental evidence in favour of this inference arises from analyzing karyotypes with NORs located at their original sites and karyotypes with NORs translocated from their original sites. The close correlation between the different rate of synthetic activity (transcription) in nucleolus formation and the comparable range of variation in aberration involvement of NORs observed in translocation lines are discussed.

Plant extracts induce chromosome aberrations and sister-chromatid exchanges in Chinese hamster ovary cells and human lymphocytes

Effects of extracts from Vicia faba were compared with those of Zea mays for the induction of sister-chromatid exchanges (SCEs) and of chromosome aberrations (CAs) in Chinese hamster ovary (CHO) cells. CA induction by the maize extract was also tested in human lymphocytes. The extracts from roots and leaves of Vicia faba induced CAs and SCEs in CHO cells. The extracts from maize leaves also induced SCEs and CAs in CHO cells, and CAs in human lymphocytes. Maize extracts were more potent in inducing SCEs than Vicia extracts and the SCE- and CA-inducing capacity of maize extracts decreased during preincubation before addition to cells.

Effects of ethidium bromide and nalidixic acid pretreatment on the induction of chromatid aberrations by TEM and maleic hydrazide in Vicia faba main root meristems

Pretreatment of Vicia faba main root meristems with ethidium bromide (EB) or nalidixic acid (NA) significantly reduced the yield of metaphases with chromatid aberrations induced by maleic hydrazide (MH), i.e., triggered clastogenic adaptation to MH. No such protection occurred when the alkylating agent triethylenemelamine (TEM) was used for challenge treatment. The differential response of pretreated cells to MH on the one hand (protection) and to TEM (no protection) on the other supports the conclusion that clastogenic adaptation is due to different inducible (repair?) functions, which eventually exert protection against clastogenic impacts.

Pretreatment of Vicia Faba Root Tip Meristems with Low Clastogen Doses Protects against Aberration Induction by Subsequent Treatments: Induction of Repair Processes?

In order to counteract potential DNA damage, organisms have evolved mechanisms to reverse, remove or tolerate such adverse influences. A distinction is made between ‘constitutive’ mechanisms, active at all times and ‘inducible’ ones that represent response to damage. The authors explore in this paper the extent to which low doses of clastogens can protect the system against higher doses. They show that one alkylating agent may substitute for another but that conditioning to induce protective effects is prevented by inhibition of protein synthesis.

Revision of SAT chromosome number in Triticum monococcum with respect to nucleolar organizers activity

SummarySix varieties of Triticum monococcum were analysed by means of the nucleolar test; i.e., estimation of the maximum number of primary nucleoli per nucleus. All of the varieties exhibited 4 primary nucleoli in telophase and early interphase. Following detailed karyological analysis four SAT chromosomes in all six karyotypes were found in accordance with the maximum nucleolar number. Secondary constrictions and microsatellites were localised on the short arms of chromosome pairs 3 and 5. A new order of the chromosomes in the idiogram of Tr. monococcum is proposed.

Effects of chromosome reconstruction on deletion clustering in Hordeum vulgare

SummaryThe barley standard karyotype, two reconstructed karyotypes with all chromosomes interdistinguishable, and four translocation lines were treated with maleic hydrazide. A specific chromosomal site in satellite chromosome 7 (segment 44 adjacent to the nucleolus organizer region) of the standard karyotype was found to represent a deletion hot spot. A sample of specifically reconstructed karyotypes were used to check whether or not transposition of the hot spot region, or changes of its neighborhood, would affect its involvement in deletions. One of the seven karyotypes (translocation line T 505 with a pair of chromosomes having both nucleolus organizer regions and satellites in opposite arms) was without deletion clustering in segment 44. At the same time, a prominent Giemsa band close to the secondary constriction was absent from segment 44. These data show that the involvement in deletions of a certain chromosome segment is modifiable in certain cases by chromosome reconstruction. Similar observations have been made in Vicia faba.

Effects of novobiocin on heat shock protection against chromatid aberration induction by triethylenemelamine (TEM) and maleic hydrazide (MH) in Vicia faba

Heat shock (10 min 40 degrees C) prior to challenge treatment with triethylenemelamine (TEM) or maleic hydrazide (MH) significantly reduced the frequency of induced chromatid aberrations in Vicia faba main root meristems. Novobiocin treatment before heat shock did not prevent heat shock protection against both clastogens; novobiocin application after heat shock prevented protective effects. These results and those obtained earlier for heat shock protection against X-ray challenge are used to discuss possible causes underlying the protective effects triggered by heat shock.

Effects of formamide on the induction of chromosome structural changes by ethyleneimine in Vicia faba

Abstract Main roots of Vicia faba , karyotype ACB, were treated with formamide (FA) alone, with ethyleneimine (EI) alone and simultaneously with formamide (FA). No increase in the spontaneous chromatid aberration rate in Vicia main root meristems have been observed after treatment with FA alone. After treatment of primary roots with EI the maximum of aberrations (about 35.2%) was found after 21 h recovery time. After combined application of EI and FA the peak of aberration was found after 27 h i.e. about 6 h later, the frequency of aberrations approximately being doubled (50.3%) as compared with EI treatment alone.