Transgenic tobacco seedlings that overexpress a cDNA encoding an enzyme with both glutathione S-transferase (GST) and glutathione peroxidase (GPX) activity had GST- and GPX-specific activities approximately twofold higher than wild-type seedlings. These GST/GPX overexpressing seedlings grew significantly faster than control seedlings when exposed to chilling or salt stress. During chilling stress, levels of oxidized glutathione (GSSG) were significantly higher in transgenic seedlings than in wild-types. Growth of wild-type seedlings was accelerated by treatment with GSSG, while treatment with reduced glutathione or other sulfhydryl-reducing agents inhibited growth. Therefore, overexpression of GST/GPX can stimulate seedling growth under chilling and salt stress, and this effect could be caused by oxidation of the glutathione pool.

No abstract

Even granting our uncertainties about parts of our model of the sulfur cycle, we can draw some conclusions from it: 1) Man is now contributing about one half as much as nature to the total atmospheric burden of sulfur compounds, but by A.D. 2000 he will be contributing about as much, and in the Northern Hemisphere alone he will be more than matching nature. 2) In industrialized regions he is overwhelming natural processes, and the removal processes are slow enough (several days, at least) so that the increased concentration is marked for hundreds to thousands of kilometers downwind. 3) Our main areas of uncertainty, and ones that demand immediate attention because of their importance to the regional air pollution question, are: (i) the rates of conversion of H(2)S and SO(2) to sulfate particles in polluted as well as unpolluted atmospheres; (ii) the efficiency of removal of sulfur compounds by precipitation in polluted air. And for a better understanding of the global model we need to know: (i) the amount of biogenic H(2)S that enters the atmosphere over the continents and coastal areas; (ii) means of distinguishing man-made and biogenic contributions to excess sulfate in air and precipitation; (iii) the volcanic production of sulfur compounds, and their influence on the particle concentration in the stratosphere; (iv) the large-scale atmospheric circulation patterns that exchange air between stratosphere and troposphere (although absolute amounts of sulfate particles involved are small relative to the lower tropospheric burden); (v) the role of the oceans as sources or sinks for SO(2).

The kinetics of H 2 S oxidation in a biofilter were evaluated and the reaction rates determined to be first-order at low concentrations (<200 ppm), zero-order at high concentrations (>400 ppm), and fractional-order in the intermediate concentration range for H 2 S in the inlet waste gas. The overall performance of the biofilter system and changes in compost properties were investigated for 200 days of operation. The compost biofiiter showed good buffering capacities to variations in gas flow rate and pollutant (H 2 S) loading impacts. Hydrogen sulfide removal efficiencies exceeding 99.9% were consistently observed. System acidification and sulfate accumulation were identified as inhibitors of required biological activity. Routine washing of the compost effectively mitigated these deficiencies. System upset was determined to be caused by compost dry-out or system overloading. Methods were developed to provide for recovery of contaminated filter material.