Lipopolysaccharide was prepared from the extracellular lipoglycopeptide produced by the lysine-requiring mutant Escherichia coli A.T.C.C. 12408 grown under lysine-limiting conditions. The lipid moiety, containing glucosamine phosphate and four fatty acids (lauric acid, myristic acid, beta-hydroxymyristic acid and palmitic acid) corresponded in composition to lipid A of known bacterial lipopolysaccharides. The components of the polysaccharide moiety were d-glucose, d-galactose, l-glycero-d-manno-heptose, 3-deoxy-2-oxo-octonic acid, ethanolamine and phosphate. These are the constituents of the polysaccharide of the cell-wall antigens from rough strains of E. coli. Lipopolysaccharides were also prepared from whole cells of E. coli 12408 grown with excess or limited amounts of lysine; they were identical in carbohydrate composition with the extracellular lipopolysaccharide. The biological properties of this material also resembled those of known lipopolysaccharides; it was antigenic, pyrogenic, toxic and had adjuvant activity.

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SUMMARYPronounced seasonal trends were observed in nitrogen availability and utilization in an acidic soil supporting Deschampsia flexuosa and a calcareous soil supporting Zerna erecta. In both soils, mineralization rates and instant inorganic nitrogen concentrations were maximum in late winter/early spring after which a rapid decline occurred. A similar seasonal pattern was evident in the levels of several nitrogen-assimilating enzymes and soluble nitrogen pools in both grasses. Fertilizer experiments indicated that in both soil tj'pes nitrate formation was limited by the ammoniuni supply. Despite differences in the major form of inorganic nitrogen supplied to the plants, Deschampsia and Zerna showed similar capacities to utilize ammonium and nitrate. It is suggested that the observed seasonal enzymic response in these native species may be an adaptation to the fluctuating and low nitrogen status of natural soils.

SUMMARYWater stress, produced either by the addition of polyethylene glycol 4000 to water culture-grown Poterium sanguisorba or by withholding water from vermiculite-grown material, reduced nitrate reductase activity, but increased the level of glutamine synthetase in shoots, in roots the levels of all the nitrogen-assimilating enzymes studied were reduced. In both tissues these changes were accompanied by a fall in soluble protein and water content and by an increase in the total a-ammo and proline pools. Marked changes in shoot individual amino acids were also induced by water stress, but were reversed when stress was relieved. The significance of these changes are discussed in relation to nitrogen assimilation and the mechanism of proline accumulation durmg drought.

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