nitrate and ammonium ions are the two major forms of nitrogen that taken up by plants, but they differ in their effects on growth and chemical composition of biochemical levels. in this research we examined the effect of nitrogen sources on growth and senescence of rice leaves in biochemical levels. our results showed that amounts of fresh and dry weights, total chlorophyll, rate of hill,s reac...

The effect of supplying either nitrate or ammonium on nitrate reductase activity (NRA) was investigated in Brassica napus seedlings. In roots, nitrate reductase activity (NRA) increased as a function of nitrate content in tissues and decreased when ammonium was the sole nitrogen source. Conversely, in the shoots (comprising the cotyledons and hypocotyl), NRA was shown to be independent of nitra...

A mmonium (NH 4 +), the substance created by the fi xation of atmospheric nitrogen (N 2), occupies a central role in cellular nitrogen metabolism. However, even though it is an important metabolite, free ammonium is present only transiently in biological systems, where it is rapidly converted into amino acids—initially glutamate and, particularly, glutamine. From there, transamination reactions...

The levels of several enzymes involved in assimilation of different nitrogen compounds were investigated in Streptomyces clavuligerus in relation to the nitrogen source supplied to the cultures. Threonine dehydratase, serine dehydratase, proline dehydrogenase, histidase and urocanase were not decreased in the presence of ammonium. The latter two enzymes were induced by histidine in the culture ...

The relative contribution of various inorganic and organic forms of nitrogen to the nitrogen requirements of picoplankton was examined with 15N tracers. Size fractionation was used to measure uptake by < l-pm size microorganisms, and inhibitors of protein synthesis were used to separate procaryotic from eucaryotic nitrogen uptake, Picoplankton utilized mainly ammonium and amino acids and only n...

We determined the quantum requirements for growth (1/ϕμ ) and fatty acid (FA) biosynthesis (1/ϕFA ) in the marine diatom, Phaeodactylum tricornutum, grown in nutrient replete conditions with nitrate or ammonium as nitrogen sources, and under nitrogen limitation, achieved by transferring cells into nitrogen free medium or by inhibiting nitrate assimilation with tungstate. A treatment in which tu...

The isolation and characterization of a Rhizobium etli glutamate auxotroph, TAD12, harbouring a single Tn5 insertion, is reported. This mutant produced no detectable glutamate synthase (GOGAT) activity. The cloning and physical characterization of a 7.2 kb fragment of R. etli DNA harbouring the structural genes gltB and gltD encoding the two GOGAT subunits GltB and GltD is also reported. In com...

A monitoring program with a weekly sampling frequency over a 15-month period indicates that urea concentrations above a certain threshold level may trigger the blooms of Alexandrium catenella in Thau lagoon. However, urea concentrations were also sometimes related to ammonium and dissolved organic nitrogen concentrations, indicating that the role of urea may not be a direct one. An original app...

Lambir Hills National Park in Malaysian Borneo is composed of dipterocarp tree species which specialize on different soil types. Although the mechanisms contributing to this distribution of tree species are unknown, one hypothesis is that tree species at Lambir differ in their preferences for different nitrogen forms. In this study we investigated (1) whether clay soil and sandy loam soil types...

Chemoautotrophic symbionts of deep sea hydrothermal vent tubeworms are known to provide their hosts with all their primary nutrition. While studies have examined how chemoautotrophic symbionts provide the association with nitrogen, fewer have examined if symbiont nitrogen metabolism varies as a function of environmental conditions. Ridgeia piscesae tubeworms flourish at Northeastern Pacific ven...