Premium
Removal of O 6 ‐methylguanine from plant DNA in vivo is accelerated under conditions of clastogenic adaptation
Author(s) -
Baranczewski Pawel,
Nehls Peter,
Rieger Rigomar,
Rajewsky Manfred F.,
Schubert Ingo
Publication year - 1997
Publication title -
environmental and molecular mutagenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1
H-Index - 87
eISSN - 1098-2280
pISSN - 0893-6692
DOI - 10.1002/(sici)1098-2280(1997)29:4<400::aid-em9>3.0.co;2-d
Subject(s) - clastogen , chromatid , vicia faba , conditioning , chemistry , toxicology , dna damage , micronucleus test , toxicity , biology , pharmacology , dna , botany , biochemistry , statistics , mathematics , organic chemistry , gene , chromosome
Previously it was shown that the clastogenic efficiency of high doses of alkylating agents in plant root meristems can be reduced significantly by conditioning pretreatment with either a low dose of the same agents, a sublethal heat shock, or heavy metal salts. The molecular mechanisms responsible for these protective effects are still unclear. Here we report on the quantification of O 6 ‐methylguanine ( O 6 ‐MeG) by immuno‐slot‐blot analysis in DNA of root tip meristems of field bean ( Vicia faba ) seedlings under conditions of clastogenic adaptation. When root tips were pretreated with a low, conditioning dose of N ‐methyl‐ N ‐nitrosourea (MNU, 10 −4 M, 1 hour) 2 hours before exposure to a high dose of the same clastogen (10 −3 M, 1 hour), the frequency of chromatid aberrations was reduced by more than 50% at a recovery time of 18 hours, as compared to treatment with the high dose alone. The same was observed when conditioning pretreatment was by a sublethal heat shock (10 minutes, 40°C) or a heavy metal salt (Cd(NO) 3 , 10 −7 M, 1 hour). The frequency of O 6 ‐MeG immediately after exposure to a conditioning and a subsequent challenge treatment was reduced by 43% as compared to treatment with only the high dose. At a recovery time of 18 hours the corresponding frequency of adducts was reduced by 68.3% (related to the initial level) after treatment with the high dose alone, and by 81.3% under adaptive conditions. Sublethal heat shock or heavy metal salt used as conditioning pretreatments also resulted in a decrease of adducts immediately after treatment with the challenge dose. From these data and from prevention of the effects by pretreatment with cycloheximide or O 6 ‐benzylguanine we conclude that under conditions of clastogenic adaptation O 6 ‐MeG is more efficiently removed from the DNA, presumably by induction of an alkyl acceptor protein such as O 6 ‐methylguanine‐DNA methyltransferase (MGMT). This could explain the observed protective effects (clastogenic adaptation). Environ. Mol. Mutagen. 29:400–405, 1997 © 1997 Wiley‐Liss, Inc.