UV-C Irradiated Research Articles

Enhancing effect of heterocyclic amines and ß-carbolines on UV or chemically induced mutagenesis in E. coli

Most heterocyclic amines and ß-carbolines — harman, norharman, harmine, harmaline — enhanced UVC (254 nm) induced mutagenesis without microsomal activation in E. coli B/r WP2. 3-Amino-1,4-dimethyl-5 H-pyrido[4,3- b]indole (Trp-P-1) was most effective and increased UVAB (295–400 nm) induced mutations as well as UVC induced ones. Trp-P-1 enhanced the frequencies of mutations induced by not only UV but also 4-nitroquinoline-1-oxide (4NQO) or 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF2), while it showed little effect on N-methyl- N′-nitro- N-nitrosoguanidine (MNNG) or γ-ray induced mutagenesis. Trp-P-1 decreased the survival of UVC irradiated cells of CM571 recA. However, these effects of Trp-P-1 on UVC induced mutagenesis and lethality were not observed in WP2s uvrA which is excisioon repair deficient. The alkaline sucrose gradient sedimentation analysis demonstrated that Trp-P-1 blocked the incision step in DNA excision repair. Further, pretreatment with Trp-P-1 before UVC irradiation showed no effect on UVC induced mutagenesis. Similar effects were also seen in the case of harman or norharman. These results suggest that heterocyclic amines and ß-carbolines inhibit DNA excision repair directly or indirectly, thus enhancing UV or chemically induced mutagenesis.

INHIBITION OF TRANSIENT GENE EXPRESSION IN CHINESE, HAMSTER OVARY CELLS BY TRIPLET‐SENSITIZED UV‐B IRRADIATION OF TRANSFECTED DNA

The biological effectiveness of thymine-thymine cyclobutane dimers specifically induced by photosensitized ultraviolet-B irradiation was analyzed by host-cell reactivation of triplet-sensitized, UV-B irradiated plasmid pRSV beta gal DNA transfected into normal and repair-deficient Chinese hamster ovary cells. For comparison, pRSV beta gal DNA was also UV-C irradiated and transfected into the same cell lines. Ultraviolet endonuclease-sensitive site induction was determined after UV-C irradiation or acetophenone-sensitized UV-B irradiation of plasmid pRSV beta gal DNA. These data were used to calculate the number of cyclobutane pyrimidine dimers required to inactivate expression of the lacZ reporter gene in each irradiation condition. Transfection with UV-C-irradiated plasmid DNA resulted in a significantly greater reduction of reporter gene expression than did transfection with acetophenone-sensitized UV-B-irradiated pRSV beta gal DNA at equivalent induction of enzyme-sensitive sites. Since only a fraction of the inhibition could be accounted for by noncyclobutane dimer photoproducts, these results suggest that cytosine-containing pyrimidine cyclobutane dimers may be more effective than thymine-thymine dimers in inhibiting transient gene expression as measured in such host-cell reactivation experiments in mammalian cells.

Hormonal and Phenolic Changes Accompanying and Following UV-C Induced Stress in Spathiphyllum leaves

Summary Leaves of the indoor ornamental plant Spathiphyllum wallisii have functional stomata only on the abaxial surface, yer irradiating the upper surface with UV-C (253.7 nm) leads to rapid closure of the stomata on the under surface, 5 or 6 cell layers away. Suspecting the intervention of chemical messengers, hormonal changes accompanying and following the 1 hour ultraviolet irradiation were studied. Within minues of such irradiation, ethylene released by the intact attached leaves more than quadrupled, but dropped to the control level within minutes of switching off the UV-C source. Sprays of the ethylene-releasing compound Ethrel had no effect on the stomatal resistance or the rate of transpiration. No evidence for a clear-cut role of ethylene in stomatal control could be obtained. The level of ABA dropped initially but then increased many-fold during the next 4 h, but during this period the stomata showed partial recovery. IAA level also decreased during the hour of irradiation, but increased dramatically up to 7 h. There was more IAA than ABA at all times and, since IAA alone promotes stomatal opening and partially overcomes the ABA-induced closure, an interplay of these two hormones is likely. Free phenolic acids extracted from UV-C irradiated leaves and freed of endogenous ABA, inhibited transpiration. Two of these compounds were putatively identified as p-OH-benzoic and proto-catechuic acids respectively, on the bases of their retention times in HPLC. The temporal sequence of hormonal and phenolic changes accompanying UV-C irradiation is: ethylene → ABA ≡ IAA → phenolic acids. Interaction among these compounds is suggested.

Dichotomy In Response To Indomethacin In Uv-C And Uv-B Induced Ultraviolet Light Inflammation

In subjects irradiated with both UV-C and UV-B ultraviolet light (UVL), 10 mug of intradermal indomethacin decreased the redness in all 13 of the UV-B irradiated areas but in only 2 of 13 of the UV-C irradiated areas. Higher doses of intradermal indomethacin (50 mug and 100 mug) decreased the redness produced by UV-C irradiation in 6 subjects. It is suggested that the failure of 10 mug of indomethacin to decrease the redness of the UV-C induced inflammation, while decreasing the redness in the UV-B induced inflammation, is consistent with the possibility that prostaglandins participate in UV-B but not UV-C induced inflammation.