Environmental and Molecular Mutagenesis - Legacy Tobacco ...

682
: 1989 EMS Abstracts 235
MODULATORY EFFECTS OF WHEAT SEEDLINC,S HGMOjF39ATE (S14) ON (,ENOTOXICITY
CF SOME SYSPEMIC PE4TICIDES . I .S . GRGVER and S•S .LacYiar, School of Life
Sciences .Guru Nangk-Dev University, Amritsar-143005, INDIA
Modulatory effects of wheat seedlings homogenate (S14) on genotoxicity
of some systemic pesticides viz . benomyl, Ekatin, . . FernoXone,
and monocrotophos have been assessed employing histidine ceversibn
assay in Salrtonella yj~urium (Ames assay) and d;romosoiosl aberrations
ih root meristems inlium =p-a . All these pesticides induced mitotic
depression and a broad spectrum of physiological (a-mitosis, stickiness,
vagrant chromosomes, laggards eta .) and .clastogenic (chromosome breaks,
ring chromosomes and micronuclei) aberrations . However, the frequency
of induced physiological aberratior.s remain unaltered by S14 homogenate
but the percentage of cells with clastogenic aberrations was reduced
significantly with the supplementation of 514 . None of these pesticides
enhanced significantly the histidine revertants in TA98> TA1V2 and
TA1535 of .5 . tvnhimurlum . No appreciable effect was observed with the
supplementation of rat liver S9 homogenate or wheat seedllno S14
homogenate .
683
GENEl`GX EVALUATION OF METASYSTUX IN CHRGMC-SOMAL ABERRATIONS AND CHLORC :-
YHYLL DEFICIENT MUTATI(~N ASSAY IN HQRDEUM VULGARE, I .S .GFGVER, Vinlta
and'H .Grover, School of Life Sciences, Guru Nanak Dev University,
Amritsai an`i3 +S .R.Govt .College for Women, Amritsar . INDIA .
Metasystox-an organophosphorus pesticide is one of the mo4t wic3ely
used pesticides whose genotoxic nature is uncertain . The present report
describes its genotoxic effect employing chr'omosoeal aberrations assay
in root meristems and pollen mother cells and chlorophyll deficient
mutation assay in }jordeum yylqAy .'It induced a significarit increase in
chromosomal aberrations in root meristems . The spectrum of chromosomal
aberrations included chromosome breaks, c-mitotic effects, leading to
polyploid cells, chromatin'bridgesn laggards .tri- and tetraPolar cells
and micioruclei . The effect was found to be "dose-dependent• Po'llen mother
cells with univalents was the moet common aberration encountered at
metaphase-I .Rarely a quadrivalent attributable to exchanges was also
noticed . Unequal distr'ibution, chro.matin bridges and laggards were also
recd rded . M2 analysis at the seedling stage revealed chlorophyll
deficient mutants
. Xa ntha, tigrina, maculata, albovirldis and virido-
chlorophyll deficient mutantsuwarrantTitsifuc~herrstudies~iccaebatteryaof
assays
684
EVOLUTIONARY SIGNIFICANCE OF MUTATION AND REPAIR . Robert H . Haynes, Department of
Biology, York University, Toronto, Canada, H3J 1P9 .
Heredity is a manifestation of the stability of genes, chromosomes and genomee
from one generation of cells and organisms to the next . Heritable variation is a
manifestation of various types of change in the genetic material of c .lls . In the
absence of mechanisms to promote an extremely high level of replicational fidelity,
the long genetic messages of contemporary organisms could not have evolved . In addition,
were it not for the existence of processes which effect the repair or bypass of
damage to DNA which arises from many ever-present natural sources, cellular activity
would collapse from what might be called 'genetic meltdown' . On the other hand, if
the various mechanisms which promote genetic stability were capable of functioning
with perfect accuracy, genetic variation, and hence evolution, also would not occur .
Many different genetic loci are involved in coding and control of the complex array
of biochemical processes which maintain genetic stability . This is consistent with
the notion that if very great fidelity is to be achieved with equipmmnt of poor precision,
extensive checking procedures must be built into the system . For optimum
economy, the 'cost' of such procedures should be just sufficient to reduce the errorrate
to a tolerable level . Thus, the genetic machinery of cells can be viewed as a
remarkable example of a highly reliable, dynamically stable system built from vulnerable
and unreliable parts . Recent work on the genetic consequences of nucleotide pool
imbalance suggests that natural selection has fashioned all major aspects of DNA
metabolism to minimise mortality and mutability . However, the existence of inducible
error-prone processing of DNA damage indicates that the maintenance of cellular viability
takes precedence over genetic fidelity .
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