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W D Stewart

Publications and source records attributed to W D Stewart.

70 records · Page 4Linked to original sources
PubMed1970

Acetylene reduction assay for determination of phosphorus availability in wisconsin lakes.

Phosphorus-starved cells of Anabaena flos-aquae rapidly increase their capacity to reduce acetylene to ethylene when they receive phosphorus. This response may be used as a bioassay for detecting available phosphorus in aquatic ecosystems. The sensitivity of the method compares favorably with conventional methods for measuring dissolved orthophosphate, and has the additional advantage that it measures available phosphorus. Studies on Wisconsin lakes show that available phosphorus generally is present, that the concentrations are higher at the lower depths than at the surface, and that there may be diurnal variations in the available phosphorus content of surface waters. Important sources of available phosphorus in Lake Mendota are the waters below the thermocline and the input from storm sewers.

Journal Article↗
PubMedDate not supplied

Cyanobacteria-eukaryotic plant symbioses.

N2-fixing heterocystous cyanobacteria develop in symbiotic association with a small number of eukaryotic plant species belonging to the algae, fungi, liverworts, ferns, gymnosperms and angiosperm. When the free-living cyanobacteria develop in symbiosis, they become modified morphologically, physiologically and biochemically. The symbiosis are relatively specific, and among the changes which occur in the endophytic cyanobacteria are increases in the size of the vegetative cells, changes in the ultrastructure of the vegetative cells, a tendency for a reduction in the filamentous habit, an increased heterocyst frequency when another photosynthetic partner is present, reduced activities of glutamine synthetase and glutamate synthase, and NH4+ release by; the endophytic cyanobacteria. These and other aspects are considered, emphasizing, in particular, work carried out in the authors' laboratory.

Cyanobacteria↗