Induced Resistance in a Desmid Closterium moniliferum

Howard, Alma; Cowie, F. G.

doi:10.2307/3574385

Cited by 21 publications

(8 citation statements)

References 14 publications

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“…For example, exposure of the alga Closterium moniliferum to 10 MeV electrons elongates the shoulder of survival curves obtained after exposure of the cells to a series of doses 4 h after the initial exposure (Howard and Cowie 1976) . It was suggested that potentially lethal damage was being repaired .…”

Section: Resultsmentioning

confidence: 99%

Human Lymphocytes Exposed to Low Doses of Ionizing Radiations Become Refractory to High Doses of Radiation as Well as to Chemical Mutagens that Induce Double-strand Breaks in DNA

Wolff

Afzal²,

Wiencke

et al. 1988

International Journal of Radiation Biology

266

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Human lymphocytes exposed to low doses of ionizing radiation from incorporated tritiated thymidine or from X-rays become less susceptible to the induction of chromatid breaks by high doses of X-rays. This response can be induced by 0.01 Gy (1 rad) of X-rays, and has been attributed to the induction of a repair mechanism that causes the restitution of X-ray-induced chromosome breaks. Because the major lesions responsible for the induction of chromosome breakage are double-strand breaks in DNA, attempts have been made to see if the repair mechanism can affect various types of clastogenic lesions induced in DNA by chemical mutagens and carcinogens. When cells exposed to 0.01 Gy of X-rays or to low doses of tritiated thymidine were subsequently challenged with high doses of tritiated thymidine or bleomycin, which can induce double-strand breaks in DNA, or mitomycin C, which can induce cross-links in DNA, approximately half as many chromatid breaks were induced as expected. When, on the other hand, the cells were challenged with the alkylating agent methyl methanesulfonate (MMS), which can produce single-strand breaks in DNA, approximately twice as much damage was found as was induced by MMS alone. The results indicate that prior exposure to 0.01 Gy of X-rays reduces the number of chromosome breaks induced by double-strand breaks, and perhaps even by cross-links, in DNA, but has the opposite effect on breaks induced by the alkylating agent MMS. The results also show that the induced repair mechanism is different from that observed in the adaptive response that follows exposure to low doses of alkylating agents.

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Section: Resultsmentioning

confidence: 99%

Human Lymphocytes Exposed to Low Doses of Ionizing Radiations Become Refractory to High Doses of Radiation as Well as to Chemical Mutagens that Induce Double-strand Breaks in DNA

Wolff

Afzal²,

Wiencke

et al. 1988

International Journal of Radiation Biology

266

View full text Add to dashboard Cite

show abstract

“…(1966), using Chinese hamster and HeLa cells, also concluded that the increase in survival occurring after trypsinization could be attributed to synchronization and accumulation of cells in a more resistant phase of the cell cycle . For Chinese hamster cells, Lehnert (1975) reported no change in sensitivity during the first 5 hours after trypsinization, but a change after 20 hours which resulted in an increased D o value and a complete loss of the shoulder region .…”

Section: Introductionmentioning

confidence: 99%

“…Resistance to ionizing radiation can be induced in several cell types and in bacteria by previous exposure to ionizing radiation and ultra-violet light (Hillova and Drasil 1967, Horsley and Laszlo 1971, Bryant 1974, Howard and Cowie 1976, Pollard and Achey 1975 . The resistance is usually detected by comparing survival curves obtained for a second series of doses with that for a series of single doses.…”

Section: Introductionmentioning

confidence: 99%

“…It has been reported recently, for example, that induced resistance occurs in crypt cells of the mouse colon after previous exposure to two conditioning doses of 1250 rad given at 6-weekly intervals (Hamilton 1978) . 190 Correspondence It has been reported that a decrease in the sensitivity of mammalian cells can take place as the time between trypsinization, plating and irradiation is increased (Barendsen and Walter 1964, Phillips and Tolmach 1964, Berry, Evans and Robinson 1966, Lehnert 1975 . In the case of human kidney cells (Barendsen and Walter 1964), the changes were attributed to a ' recovery ' from the trauma of trypsinization .…”

Section: Introductionmentioning

confidence: 99%

“…The resistance is usually detected by comparing survival curves obtained for a second series of doses with that for a series of single doses. Induced resistance can take the form of an increase in shoulder width of the second dose-survival curve (Horsley andLaszlo 1971, Howard andCowie 1976), but in other systems is manifested as a decreased slope with a reduced extrapolation number (Hillova andDrasil 1967, Bryant 1976) . This type of induced resistance may result from an increase in the rate of repair of radiation damage after the second dose has been given (Bryant 1975(Bryant , 1976 .…”

Section: Introductionmentioning

confidence: 99%

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