Showing papers by "Miguel G. Guerrero published in 1989"

Determination of intracellular nitrate.

Abstract: A sensitive procedure has been developed for the determination of intracellular nitrate. The method includes: (i) preparation of cell lysates in 2 M-H3PO4 after separation of cells from the outer medium by rapid centrifugation through a layer of silicone oil, and (ii) subsequent nitrate analysis by ion-exchange h.p.l.c. with, as mobile phase, a solution containing 50 mM-H3PO4 and 2% (v/v) tetrahydrofuran, adjusted to pH 1.9 with NaOH. The determination of nitrate is subjected to interference by chloride and sulphate when present in the samples at high concentrations. Nitrite also interferes, but it is easily eliminated by treatment of the samples with sulphamic acid. The method has been successfully applied to the study of nitrate transport in the unicellular cyanobacterium Anacystis nidulans.

Nitrogen-Fixing Cyanobacterium with a High Phycoerythrin Content

Abstract: The elemental and molecular composition, pigment content, and productivity of a phycoerythrin-rich nitrogen-fixing cyanobacterium—an Anabaena strain isolated from the coastal lagoon Albufera de Valencia, Spain—has been investigated. When compared with other heterocystous species, this strain exhibits similar chlorophyll a, carotene, and total phycobiliprotein contents but differs remarkably in the relative proportion of specific phycobiliproteins; the content of C-phycoerythrin amounts to 8.3% (versus about 1% in the other species) of cell dry weight. Absorption and fluorescence spectra of intact phycobilisomes isolated from this Anabaena sp. corroborate the marked contribution of phycoerythrin as an antenna pigment, a circumstance that is unusual for cyanobacteria capable of fixing N2. The pigment content of cells is affected by variations in irradiance and cell density, these adaptive changes being more patent for C-phycoerythrin than for phycocyanins. The Anabaena strain is clumpy and capable of rapid flocculation. It exhibits outdoor productivities higher than 20 g (dry weight) m−2 day−1 during summer.

The Photosynthetic Assimilation of Nitrate and Its Interactions with CO2 Fixation

Abstract: Photosynthesis is usually identified with the light--driven formation of carbohydrates and oxygen from CO2 and water. This formulation ignores, however, the basic fact that in the photosynthetic process not only CO2, but also the oxidized forms of other primordial bioelements are reduced and incorporated into cell material. Actually, photosynthesis drives a number of biosynthetic pathways involved in the assimilation of inorganic carbon, nitrogen and sulfur. At the expense of sunlight energy, unstable energy-rich products -cell material and oxygen- are synthesized from fully oxidized substrates with no useful chemical potential, namely water, carbon dioxide, nitrate, sulfate and phosphate (Losada and Guerrero, 1979; Losada et al., 1987).