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Cucumber plants (Cucumis sativus L.) were grown under controlled conditions and fumigated with either O3, diluted automobile exhaust or a combination of both. The ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) was estimated as a measure of PSII activity Activities of the enzymes catalase, glutathione reductase and guaiacol-dependent peroxidase and contents of the antioxidants ascorbate and glutathione were assayed as potential indicators of oxidative stress. The behavior of catalase and of PSII are of particular diagnostic interest because they require continuous repair in light. Exposures of up to 13 days to moderate concentrations of the pollutant gases alone did not induce striking changes in any of the activities that were assayed. A lso when the plants were subjected to an additional stress treatment by exposing them to 4 short cold treatments (2h each at 0 - 4 °C in light on days 12-15 after sowing) which induced marked declines of the Fv/Fm ratio, the chlorophyll content and the catalase activity, these cold-induced symptoms of photodamage were not significantly enhanced by the fumigation treatments. However, increases of the activities of glutathione reductase and peroxidase observed during a period of recovery following the cold-exposures were markedly higher in O3-fumigated plants, as compared to plants grown in filtered air or fumigated with car exhaust alone. The results emphasize that effects of moderate pollutant exposures may be latent or delayed over long time periods and that defence responses can be enhanced when plants are exposed to additional, naturally occurring stress situations.
The radiation-sensitive mutant pso4-1 of Saccharomyces cerevisiae shows a pleiotropic phenotype, including sensitivity to DNA cross-linking agents, nearly blocked sporulation and reduced mutability. We have cloned the putative yeast DNA repair gene PSO4 from a genomic library by complementation of the blocked UV-induced mutagenesis and of sporulation in diploids homozygous for pso4-1. Sequence analysis revealed that gene PSO4 consists of 1512 bp located upstream of UBI4 on chromosome XII and encodes a putative protein of 56.7 kDa. PSO4 is allelic to PRP19, a gene encoding a spliceosome-associated protein, but shares no significant homology with other yeast genes. Gene disruption with a destroyed reading frame of our PSO4 clone resulted in death of haploid cells, confirming the finding that PSO4/PRP19 is an essential gene. Thus, PSO4 is the third essential DNA repair gene found in the yeast S.cerevisiae.
A non-radioactive cell-free assay was developed to quantitatively determine inhibition of plant-type phytoene desaturase by bleaching herbicides. An active desaturase was prepared from an appropriately cloned E. coli transformant. Another E. coli transformant was used to produce the required phytoene. Phytofluene and t-carotene, the products of the desaturase reaction, were either determined by HPLC or optical absorption spectra. Enzyme kinetics and inhibition data for the bleaching tetrazole herbicide WL110547 are presented as an example.