Reversibility of X irradiation-induced effects in dry biological systems

Abstract

There are two general classes of reversible events or states that must be distinguished. There are radiation-induced biological events that may be reversible; and there are reversible radiation-induced events that lead to these reversible biological events or, perhaps, to irreversible ones. We should expect that the processes of reversal will be different in the two general categories. For instance, the repair of a broken chromosome should depend upon factors and show characteristics that are different from those exhibited by reversal or removal of the radiation-induced chemical species that precede in time and would lead to the chromosome break if allowed to remain in the cell. Both are examples of reversible radiation effects. One is a %o-chemical" or "enzymatic" type of reversibility; the other is chemical or physicochemical. The purpose of this paper is to examine in bacterial spores radiation effects that probably are physico-chemical in nature, with the particular purpose of separating the reversible from the irreversible (or those that are reversed with greater difficulty), and of noting the effect on the measured response of the cell to the varying degrees of rcversibility that we can observe.The end-points we shall examine are biological in nature-the ability of an irradiated spore to germinate and develop into a cell that can then go through approximately 10 fissions. The radiation effects that we shall manipulate are physicochemical, not biological, in nature. It is important to appreciate that, in this way, we may gain an understanding of the relationship between physical and chemical effects of radiation in cells and the biological consequences of these effects. This understanding is impossible, or nearly so, if one examines only one or the other.The system that we use is particularly suitable for this kind of analysis, for in this almost dry cell no metabolic activity occurs before, during, or after irradiation. The varying biological effects we see can certainly be ascribed to antecedent physical and chemical effects; and the use of the biological end-point of colony formation measures directly, in one respect, the biological importance of these physico-chemical events. We should expect to recognize precise behavior on the psrt of the reversal processes if we can isolate them for measurement. We should expect to be able to predict the consequences of the rules that we recognize, even though the interrelations among them may be complex. This paper will present the results of an examination of the radiation response in terms of subunits that are experimentally recognizable and measurable. It will demonstrate their characteristics and behavior and will show that understanding of these elements of the over-all radiation response must be realized before an understanding of complex responses to radiation is possible.

Differential Modification of Oxic and Anoxic Components of Radiation Damage inBacillus MegateriumSpores by Caffeine

“…Employing this technique in barley seeds, Kesavan and his co-workers (Kesavan 1973, 1978, Kesavan and Ahmad 1974a, b, Kesavan and Afzal 1975, Kesavan and Dodd 1976, Kesavan and Nadkarni 1977 have demonstrated that caf reported to enhance the radiosensitivity of the seeds via inhibition of biochemical repair mechanisms (Yamamoto andYamaguchi 1969, Ahnstrom 1974) affords protection against oxic damage (equivalent to that component involving long-lived radicals in dried bacterial spores, class III of Powers (1961), or A n of Dodd and Ebert (1970) in Osmunda spores). These studies by Kesavan and co-workers also revealed that only in the absence.of the radiationinduced precursors of oxic damage ( 2 -sensitive sites) does caf dramatically potentiate the anoxic component of radiation damage.…”

Interactions of Oxygen at High Pressure and Radiation in Drosophila

“…However, radiation preceding exposure to oxygen at high pressure did not reveal such large and consistent accelerations of the acute neurological effects of OHP. Persistence of organic peroxy radicals probably is of relatively short duration in animals such as fruit flies as compared to long persistence of organic radicals in bacterial spores (12) or seeds (13). The long persistence of a significant number of free radicals in hydrated animal tissues is extremely improbable according to present concepts.…”

Environmental Conditions That Modify Plant Response to Neutron Irradiation.

“…Neary jit al. [5] reported an OER of 1,4 for reduction in elongation of broad bean roots, and Hall [6] in the same system, obtained the ratio of 1.66 for both 14 MeV neutrons and for californium 252 [73, 637a of the dose of which is contributed by fission spectrum neutrons having an average energy of 2*3 MeV and a modal energy of about 1 MeV* Corresponding , measures on barley roots gave an OER of 1*92 for 14 MeV neutrons, compared Powers [32] demonstrated three classes of radiation damage to the spores: that produced by I) short-lived completely oxygen-independent changes; II) short-lived, oxygen-dependent species (seen only when oxygen is present during irradiation); and III) interactions between radiation-induced free radicals (which may be relatively long lived) and oxygen* To these may be added a fourth class of radiobiological damage, observed in the dry barley seed system [33], which appears to be independent of oxygen and long-lived free radicals and develops very slowly during storage after irradiation. Neutrons act preferentially on locus l t whereas the sulfonates mutate preferentially loci u, £ and c-and produce none at 1 [463* Similarly, for ^rectoides mutants, there is some evidence that the response of different loci to different mutagens is not the same [47] O For example, locus £ mutates more frequently after treatment with sparsely ionizing radiations (x and y rays) compared with densely ionizing radiations (protons and neutrons)* For locus c, however, neutrons seem to be equally efficient if not more so than x rays.…”