No abstract

Genetic modiWcation of nitrogen metabolism via bacterial NADPH-dependent glutamate dehydrogenase (GDH; E.C.4.1.2.1) favorably alters growth and metabolism of C3 plants. The aim of this study was to examine the eVect of expression of GDH in the cytoplasmic compartment of Zea mays cells. The gdhA gene from Escherichia coli , that encoded a NADPH-GDH, was ligated to the ubiquitin promoter that incorporated the Wrst intron enhancer and used to transform Z. mays cv. 'H99' embryo cultures by biolistics. R0-R3 generations included selfed inbreds, back-crossed inbreds, and hybrids with B73 derivatives. The lines with the highest GDH speciWc activity produced infertile R0 plants. The highest speciWc activity of GDH from the fertile Z. mays plants was suYcient to alter phenotypes. Plant damage caused by the phosphinothricin in gluphosinate-type herbicides, glutamine synthetase (GS; EC 6.1.3.2) inhibitors, was less pronounced in Z. mays plants with gdhA pat than in gusA pat plants. Germination and grain biomass production were increased in gdhA transgenic plants in the Weld during seasons with signiWcant water deWcits but not over all locations. Water deWcit tolerance under controlled conditions was increased. Crops modiWed with gdhA may have value in semi-arid locations.

The utilization of actinomycetes as potential soybean (Glycine max (L.)) co-inoculants was evaluated. Soil samples from Carbondale and Belleville, Ill., were used to inoculate pre-germinated soybean plants to determine antibiotic sensitivity in the native Bradyrhizobium japonicum population. Sensitivity was in the order kanamycin > tetracycline > oxytetracycline > rifampicin > neomycin. Antagonism by five actinomycete cultures toward seven test strains of B. japonicum was also assessed. The ranking average inhibition (across all seven B. japonicum strains) by these actino mycetes was Streptomyces kanamyceticus = Streptomyces coeruleoprunus > Streptomyces rimosus > Streptomyces sp. > Amy colatopsis mediterranei. Ten antibiotic combinations were used to isolate antibiotic-resistant mutants of B. japonicum I-110 and 3I1B-110 via successive cycles of mutation. Eighty-one antibiotic-resistant strains were isolated and tested for symbiotic competency; nine of which were selected for further characterization in a greenhouse pot study. Few differences in nodule number were caused by these treatments. Nodule occupancy varied from 0% to 18.3% when antibiotic-resistant strains of B. japonicum were used as the sole inoculants. However, when three mutant strains of B. japonicum were co-inoculated with S. kanamyceticus, significant increases in nodule occupancy (up to 55%) occurred. Increases in shoot nitrogen composition (27.1%-40.9%) were also caused by co-inoculation with S. kanamyceticus.

The acidulation effects of the prolonged use of nitrogenous fertilizers on selected chemical and microbiological properties of a silt loam soil (Typic Ochraqualf) were assessed.Soil samples were collected from experimental plots initially established in 1971 that were annually treated with ten N fertilizer treatments and planted to corn. Residual soil acidity found to be associated with 9 annual applications of the N fertilizers was of the order: (NH 4 ) 2 SO 4 > NH 4 C1 > anhydrous NH 3 (at 300 kg N/ha) = NH 4 NO 3 > urea = ureaform = anhydrous NH 3 (at 150 kg N/ha) > Ca(NO 3 ) 2 NaNO 3 . Extractable P, Fe, Mn and Al followed a pattern of increasing availability with a decrease in soil pH. Exchangeable Ca and Mg levels were significantly higher in those treatments that did not show a significant decrease in soil pH over the 9-year duration.Significant differences by N treatment among selected microbial groups were also determined. The annual mean counts of soil 1377 1378 KHONJE, VARSA, AND KLUBEK fungi were significantly higher for the most and least acidifying treatments, namely ammonium sulfate and sodium nitrate.However, the mean counts of soil bacteria and actinomycetes were non-significant for any of the fertilizer treatments although the counts of both microbial groups declined with the addition of N.Significant differences in the mean counts of nitrifying and denitrifying bacteria were obtained with the ammonium sulfate treatment showing the greatest reduction in MPN counts. Microbial diversity (H') indices were also determined and correlated with soil pH. A quadratic relationship was determined for phyleal diversity (the total population of bacteria, actinomycetes and fungi) with soil pH, while a linear function best described physiological diversity (the nitrifying and denitrifying bacteria) versus soil pH.