Environmental and Molecular Mutagenesis - Legacy Tobacco ...

171
CYTOLOGICALEFFECTS OF ALUMINIUM IN PLANT ROOTS
G . Fiskesjt9, Institute of Genetics, University of Ltatd, Sweden
Structures of a new type ("A1-stnictures") have been discovered in the oyEoplasta of
root cells of certain plants treated with altzainitmt ions (A13+) . Material leaches out
frotn the nuclei particularly of root cap cells, forming oblong structures one in each
cell, eventually dividing into two equal-sized structures, one at each end of the cell
with the nucleus in between . Feulgen/Light Green staining of the Al-structures indicates
that they possibly are connected with IaiA and rwcleoli(Fiskesjt5 1983) . Lightand
transtnission electron microscopy of sectioned material of Al-treated cells
yielded new aspects on the structure of cytoplasm and cell arambrane(Fiakesj8 et al .
1989, in press) . The current acidification of forest soils induces increase of Al in
solution in the soil . A13+ ions in concentrations around 20 mg/L cause severe damage
to Allitnn roots, and concentrations of this strength have actually been fotatd in forest
soil solutions when pH decreases towards 4 . The specific Al-structures which
were first found in Alliua roots after A1-treatments, have later been found also when
Alliun roots were grown in Al-rich forest soil solutiens(Berggren & Fiskesj8 1987) .
Al-structures have been found in two Allium species(oepa and schoemphrasum) and in
growth-restricted forest roots after A1-treatments(e .g . Picea abies, Fagus silvatica)
(Fiskesj8, in preparation) . Thus, A13+ ions undoubtedly ootttribute to forest damage
by interfering with root cell na:tabolism . The Al-structures may be a general response
of plants to Al . kbether the Al-structures actually oontain Al, and whether there is
a oonnection between the formation of the structures and the function of the nucleoli
are questions which remain to be answered .
172
DNA-DAMAGE INDUCIBLE GENES IN MAMMALIAN CELLS, Albert J . Fornace Jr., N .C .I .,
N .I .H ., Bethesda, MD 20892 .
Based on the results of others in bacteria and yeast, many genes would be expected to be DNA-damage
inducible (DDI) in mammalian cells ; some may represent specific responses to DNA damage, while others
may be general stress responses to cell injury . A variety of mammalian genes, such as metallothionein,
collagenase, c jos, ubiquitin, and B-polymerasel, have been found to be DDI by our group and/or other
investigators . Most of these examples probably represent general stress responses since they were induced
by unrelated agents such as heat shock and/or activators of protdin kinase C. However, B•polymerase
mRNA was found to be specifically induced only by alkylating agents and similar agents that produce DNA
damage repaired by a mechanism involving B-polym erasel . The 8-polymerase gene had several properties
in common with bacterial genes that are specifically DDI : low abundance, rapid induction of 2-10 fold, and
induction specific for DNA damage . An approach to isolate cDNA clones of other such DDI genes was
developed using hybridization subtraction at low ratios of RNA :cDNA2. 49 different cDNA clones were
isolated that coded for transcripts rapidly induced 2-28 fold by UV radiation in Chinese hamster cells2 .
Many of these transcripts were induced only by DNA-damaging agents ; these DDI cDNA clones were
divided into 2 classes. In Class I, only UV radiation and other UV-mimetic agents were effective inducing
agents, while in Class II other base damaging agents such as alkylating agents were also inducing agents .
Characterization of individual DDI cDNA clones will be presented including evidence that a Class I
member (DDlA18) encodes a nucleic acid single strand binding protein, and that several Class II genes are
coordinately regulated and may represent members of the same rqulon . These results support the
conclusion that multiple transcripts in mammalian cells are specifically induced by DNA damaging agents,
Ind that their protein products may be involved in the cellular response to such damage .
Fornace AJ. Jr ., Zmudka, B .Z., Hollander, M .C., and Wilson, S .H .: Molec. Cell . Biol . 9: 851-853,1989 .
2 Fornace AJ. Jr ., Schakh, H., and Alamo, I. Jr.: Proc . NaO . Acad . Sci . USA 85 : 8800-8804,1988.
173
ACCUMULATION OF DNA SINGLE-STRAND BREARS AND POSSIBLY ARTIPACfUAL IIDS RESPONSE IN RAT
HEPATOCYTES BY DIFLOXACIN . F . L . Fort, X . A . Cifone, and R . 0 . Curren, Abbott Lahe,
Abbott Park, IL, Razleton Labs, Rensington, MD and Microbiological Associates,
Rockville, MI
Difloxacin is a quinolone antibacterial which has been found positive for
unscheduled DNA synthesis (UDS) activity in rat hepatocyte cultures . Skare, et al .
(Mutat . Res . 172 : 77-87, 1986) reported an artifactual UDS response with sodium
fluoride presumably due to precipitahle complex formation involving fluorine ion and
[3N]thymidine triphosphate . Since difloxacin has low aqueous solubility and is difluorinated,
it is possible that the positive UDS response might be artifactual by a
similar mechanism . As a preliminary test of this hypothesis, difloxacin was tested in
a modified UDS protocol in which the culture medium containing drug was filtered prior
to treatment of hepatocyte cultures . Under these conditions difloxacin did not induce
a UDS response even though the drug concentration after filtration was equal or higher
than that when a UDS response was obtained without filtration . Therefore, the UDS
response may be artifactual ; further studies are necessary to prove this . To further
test the mechanism for the UDS response, hepatocyte cultures treated with difloxacin
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
1989 EMS Abstracts 61
Notes