By the method of gel electrophoresis, radiation-induced DNA single- and double-strand breaks (SSB, DSB) were studied with a model system of pBR322 solution in vitro in the presence of •OH radical scavengers, mannitol and TE (10-2 mol dm-3 Tris and 10-3 mol dm-3 ethylene diamine tetra-acetic acid). Experiments showed that SSB resulted from one-hit events of radiation energy deposition and DSB resulted from both one-hit and two-hit energy deposition events and so were distinguished into two classes of αDSB and βDSB. Moreover, α/β, where a is the number of DSB per unit dose induced in one irradiation event and β the number of DSB per unit squared dose induced by the combination of two independent SSB, was related to the scavenging capacity, s, and for σ<108 s-1, αDSB predominate over DSB. On the other hand, if σ<2´108 s–1, the measured G(αDSB) decreased in parallel with G(SSB), i.e., G(αDSB)/G(SSB) was a constant. When σ>2×108 s-1, G(αDSB) decreased slightly so that the ratio of αDSB to SSB evidently increased. Therefore, αDSB could be induced by the radical transfer mechanism for σ<2×108 s-1 and contrarily produced by the local multiply damaged sites (LMDS) mechanism for σ larger than this value. In addition, the distance for two independent complementary SSB forming αDSB was deduced, but no apparent variation of it was found in the wide σ range from ～105 to ～109 s-1, which shows that the DNA steric structure was not influenced by mannitol.

Discharge was performed against ammonia water using a graphite rod as the anode and a silver thread as the cathode under an Ar atmosphere. HPLC and thin layer chromatograph (TLC) analyses showed that three kinds of amino acids were produced in the reaction mixture. As the graphite anode is the solitary source of carbon in the system, it is considered that amino acids have been produced by synthetic reaction between graphite and ammonia water. Thus, our results provide a possible way of formation of amino acids from elemental carbon on the primitive earth. In ad-dition, the mechanism for the production of amino acids is discussed and the yields of different amino acids are pre- sented.

Glow-discharge experiments were performed against water using a graphite rod as the anode and a silver thread as the cathode under an Ar atmosphere. UV-spectrum, FT-IR, 1H-NMR spectrum and GC-MS analyses of the solutions irradiated with plasma were studied. It was found that a small amount of carbon was transferred from anode into water and some organic compounds were produced by reaction between carbon and water. Among those, formic acid, acetic acid and propanoic acid were identified as the main products.

An arc-discharge was carried out to a mixture of ethanol and heavy water under a nitrogen atmosphere. GC-MS analysis showed that DCH2CH2OH and DOCH2CH2OH were produced. This result implies the decomposition of water molecules, which possibly serves as an initial step for the reaction in aqueous solution. In addition, CH3COOD and HOCH2CH2ND2 were also identified in the products, and it was considered that the "nitrogen deposition" effect was caused by capture of D from D2O with N

The possible mechanism of a radiationinduced bystander response was investigated by using a high-LET heavy particle microbeam, which allows selected cells to be individually hit with precise numbered particles. Even when only a single cell within the confluent culture was hit by one particle of 40Ar (～1260keV/μm) or 20Ne (～380 keV/μm), a 1.4-fold increase of micronuclei (MN) was detected demonstrating a bystander response. When the number of targeted cells increased, the number of MN biphasically increased; however, the efficiency of MN induction per targeted cell markedly decreased. When 49 cells in the culture were individually hit by 1 to 4 particles, the production of MN in the irradiated cultures were ～2-fold higher than control levels but independent of the number and LET of the particles. MN induction in the irradiatedculture was partly reduced by treatment with DMSO, a scavenger of reactive oxygen species (ROS), and was almost fully suppressed by the mixture of DMSO and PMA, an inhibitor of gap junctional intercellular communication (GJIC). Accordingly, both ROS and GJIC contribute to the above-mentioned bystander response and GJIC may play an essential role by mediating the release of soluble biochemical factors from targeted cells.-Shao, C., Furusawa, Y., Kobayashi, Y., Funayama, T., Wada, S. Bystander effect induced by counted high-LET particles in confluent human fibroblasts: a mechanistic study. FASEB J. 17, 1422-1427 (2003)