We established basis for a datetelling method of leaves (Tillandsia spp.) consumed by Tremarctos ornatus by determining or detecting the presence of microorganisms. We used samples from the field that corresponded to different states of decomposition. The samples (2 cm from the leaf base consumed by the animal) were processed in the laboratory, characterized and determined. Cocobacilli (Pseudomonas sp.) and negative bacilli Gram were the most common bacteria morphotypes, the first were founded on samples from all ages and the second on samples no older than six months. Positive cocobacili Gram (Bacillus sp.); were just present in samples between one and three months old. Positive Gram bacilli occurred only in samples no older than a month, cocos and diplococos in samples between five and six months. Four fungus morphotypes were found, two of them being Mucor sp., and Trichoderma sp., in addition to Epicoccum sp., Alternaria sp., Rhizoctonia sp. Trichoderma was associated with at least one more kind of fungus, for samples to older than one month, but no older than five months.

We established basis for a datetelling method of leaves (Tillandsia spp.) consumed by Tremarctos ornatus by determining or detecting the presence of microorganisms. We used samples from the field that corresponded to different states of decomposition. The samples (2 cm from the leaf base consumed by the animal) were processed in the laboratory, characterized and determined. Cocobacilli (Pseudomonas sp.) and negative bacilli Gram were the most common bacteria morphotypes, the first were founded on samples from all ages and the second on samples no older than six months. Positive cocobacili Gram (Bacillus sp.); were just present in samples between one and three months old. Positive Gram bacilli occurred only in samples no older than a month, cocos and diplococos in samples between five and six months. Four fungus morphotypes were found, two of them being Mucor sp., and Trichoderma sp., in addition to Epicoccum sp., Alternaria sp., Rhizoctonia sp. Trichoderma was associated with at least one more kind of fungus, for samples to older than one month, but no older than five months.

Based on an anatomical comparison between Eremotherium rusconii and Bradypus variegatus and a literature review, similarities and differences between these species were established in an attempt to explain the extinction of E. rusconii. Proportions between femur and humerus, scall, hair, nails and metabolism were compared. Based on this, it appears that B. variegatus survival was related to its smaller size and feeding habits.

Based on an anatomical comparison between Eremotherium rusconii and Bradypus variegatus and a literature review, similarities and differences between these species were established in an attempt to explain the extinction of E. rusconii. Proportions between femur and humerus, scall, hair, nails and metabolism were compared. Based on this, it appears that B. variegatus survival was related to its smaller size and feeding habits.

Nitrate transport by Synechococcus sp. strain PCC 7942 cells was inhibited by ammonium and by inhibitors of CO 2 fixation. Ammonium assimilation inhibitors, such as l ‐methionine d,l ‐sulfoximine, were known to prevent the negative effects of ammonium and of inhibitors of CO 2 fixation on nitrate uptake, leading to propose that CO 2 fixation was required to counteract the feed‐back inhibition of nitrate assimilation. In NR‐less mutants, l ‐methionine d,l ‐sulfoximine prevented the negative effects of ammonium on nitrate transport, but not always prevented those of inhibiting CO 2 fixation. The carboxy‐terminal domain of the NrtC subunit of the nitrate transporter has recently been identified as a regulatory domain involved in N‐control. The mutant strain NC2, constructed by deleting the 3′ portion of nrtC , showed high nitrate transport activity insensitive to ammonium but sensitive to inhibitors of CO 2 fixation. These findings indicate that the C‐control and the N‐control of nitrate transport are independent at both the physiological and the molecular level.

In Synechococcus sp. strain PCC 7942, an ATP-binding cassette transporter encoded by the genes nrtA, nrtB, nrtC, and nrtD mediates active transport of nitrate and nitrite, which is inhibited by ammonium, a preferred source of nitrogen for the cyanobacterium. One of the ATP-binding subunits of the transporter, NrtC, has a distinct C-terminal domain of 380 amino acid residues. A mutant NC2, constructed by removal of this domain using genetic engineering techniques, assimilated low concentrations of nitrate and nitrite and accumulated nitrate intracellularly, showing that the domain is not essential for the transporter activities. Assimilation of low concentrations of nitrite was only partially inhibited by ammonium in NC2 but was completely inhibited in the wild-type cells. Cells of NC2 and its derivative (nitrate reductase-less strain NC4) carrying the truncated NrtC but not the cells with the wild-type NrtC accumulated nitrate intracellularly in the presence of ammonium in medium. These findings indicated that the C-terminal domain of NrtC is involved in the ammonium-promoted inhibition of the nitrate/nitrite transporter. In the presence of ammonium, NC2 could not assimilate nitrate despite its ability to accumulate nitrate intracellularly, which suggested that reduction of intracellular nitrate by nitrate reductase is also subject to inhibition by ammonium.

A kinetic study of sodium-dependent nitrate transport in the cyanobacterium Anacystis nidulans R2 has been performed by following intracellular accumulation of nitrate in intact cells of the mutant strain FM6, lacking nitrate reductase activity and unable, therefore, to reduce the transported nitrate. Initial transport rates were determined at different external fixed sodium and varying nitrate concentrations and, conversely, at different fixed nitrate and varying sodium concentrations. The resulting kinetic pattern has the best fit to a reaction mechanism model in which sodium nitrate is the substrate for the transporter and sodium behaves additionally as a non-essential activator of the system. Half-saturation constants for the substrate sodium nitrate (1.6 +/- 0.2 mu M) and the activator sodium (0.36 +/- 0.04 mM) have been calculated. The operation of such a sodium/nitrate symport system, driven by the energy of the Delta<(mu)over tilde>(Na+) across the plasma membrane, provides the basis for energy coupling between uphill nitrate and downhill sodium transport into Anacystis cells.

Cytoplasmic membranes prepared from nitrate-grown Anacystis nidulans cells exhibit a Mg2+-dependent protein kinase activity able to phosphorylate in vitro plasma membrane polypeptides with molecular masses of 98, 93, 83, 47, 44 and 31 kDa. The protein kinase activity was inhibited in cytoplasmic membrane preparations from nitrate-grown cells which had been exposed to ammonium for 5 min. Parallely, ammonium exposure also resulted in a more than two-fold activation of an alkaline phosphatase activity present in the soluble fraction. These results are discussed in relation to the well-known inhibition by ammonium of nitrate transport activity, and a hypothesis for the regulatory mechanism involved is presented.

Nitrate reductase (NR, NADH:nitrate oxidoreductase, EC 1.6.6.1) activity from leaves of barley (Hordeum vulgare L. cv. Hassan) is rapidly and reversibly inactivated during a light‐dark transition. A hyperbolic correlation exists between in vivo rates of CO2 fixation and extractable NR activity from the leaves, and feeding hexose and hexosephosphate protects against the dark‐inactivation; indicating that carbon‐assimilation products are regulatory factors of NR activity mediating both the light‐dark modulation and its dependence upon CO2 fixation. To corroborate this point, the effect of inhibiting CO2 fixation on NR activity in barley leaves has been analyzed. Glycolaldehyde (50 mM), an inhibitor of the regeneration phase of the Calvin cycle, was fed through the transpiration stream and inhibited CO2 fixation by more than 80% at the same time as it produced a parallel inhibition of NR light‐activation. Feeding mannose (10 mM), inhibited CO2 fixation by 35% but did not affect NR activity in illuminated leaves and completely protected against dark‐inactivation. Interestingly, feeding inorganic phosphate, Pi, (10 mM) alone or together with mannose also protected NR activity against dark‐inactivation. The mannose effect could be interpreted in terms of accumulation of mannose 6‐phosphate, an analog of glucose 6‐phosphate. After feeding either 10 mM glucose or dihydroxyacetone phosphate, NR activity from darkened leaves was significantly higher than that of darkened control leaves fed with water (P< 0.03). These treatments, as well as Pi feeding, also produce some increase in extractable NR activity from illuminated leaves. The results indicate that factors increasing the levels of hexose‐ and triose‐phosphate have positive effects on NR activation, supporting the contention that the NR activation system is sensitive to carbon‐assimilation products.

Nitrate reductase (NR, NADH:nitrate oxidoreductase, EC 1.6.6.1) from barley (Hordeum vulgare L. cv. Hassan) leaves was inactivated during a light-dark transition, losing approx. 50% of activity after 30 min of darkness. The dark inactivation was reversed by illumination of the seedlings, the kinetics of reactivation being similar to those of inactivation. High extractable NR activity and significant differences between illuminated and darkened leaves were observed in media containing EDTA and inorganic phosphate (Pi). Addition of Ca2+ ions during extraction and assay decreased NR activity from illuminated and darkened leaves, enhancing the light-dark difference. While no clear correlation could be found between irradiance and NR activity, a hyperbolic correlation appeared between extractable NR activity and in-vivo rates of CO2 fixation, indicating that NR activation follows saturation kinetics with respect to CO2 fixation. Furthermore, hexoses and hexose-phosphates fed to the leaves via the transpiration stream protected against the dark-inactivation of NR. The results indicate that carbon-assimilation products are regulatory factors of NR activity in barley leaves, mediating both the light-dark modulation of NR and its dependence upon CO2 fixation.

Journal of PhycologyVolume 29, Issue 4 p. 389-395 SODIUM-DEPENDENT NITRATE TRANSPORT AND ENERGETICS OF CYANOBACTERIA Catalina Lara, Corresponding Author Catalina Lara Instituto de Bioquimica Vegetal y Fotosintesis, Universidad de Servilla-CSIC, Apdo, 1113, 41080-Servilla, SpainAuthor for reprint requests.Search for more papers by this authorRocio Rodriguez, Rocio Rodriguez Instituto de Bioquimica Vegetal y Fotosintesis, Universidad de Servilla-CSIC, Apdo, 1113, 41080-Servilla, SpainSearch for more papers by this authorMiguel G. Guerrero, Miguel G. Guerrero Instituto de Bioquimica Vegetal y Fotosintesis, Universidad de Servilla-CSIC, Apdo, 1113, 41080-Servilla, SpainSearch for more papers by this author Catalina Lara, Corresponding Author Catalina Lara Instituto de Bioquimica Vegetal y Fotosintesis, Universidad de Servilla-CSIC, Apdo, 1113, 41080-Servilla, SpainAuthor for reprint requests.Search for more papers by this authorRocio Rodriguez, Rocio Rodriguez Instituto de Bioquimica Vegetal y Fotosintesis, Universidad de Servilla-CSIC, Apdo, 1113, 41080-Servilla, SpainSearch for more papers by this authorMiguel G. Guerrero, Miguel G. Guerrero Instituto de Bioquimica Vegetal y Fotosintesis, Universidad de Servilla-CSIC, Apdo, 1113, 41080-Servilla, SpainSearch for more papers by this author First published: August 1993 https://doi.org/10.1111/j.1529-8817.1993.tb00139.xCitations: 21AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume29, Issue4August 1993Pages 389-395 RelatedInformation

The influence of nitrate and ammonium assimilation on the flow of recently fixed carbon has been determined in intact Anacystis nidulans cells actively fixing CO2. Assimilation of nitrate or ammonium resulted in substantial increases in the incorporation of carbon into acid-soluble metabolites, the magnitude of the effect being dependent on the irradiance. The radiolabel in sugar phosphate was virtually unaffected by nitrogen assimilation, whereas that in organic acids and, in particular, in amino acids was markedly increased. Enhancement of carbon incorporation into amino acids induced by nitrogen assimilation was not accompanied by parallel increases in the size of the amino acid pools. This resulted in an appreciable increase of the specific radioactivity of most amino acids under conditions of nitrogen assimilation. The data indicate that nitrate and ammonium assimilation induce an enhancement of carbon flow through the glycolytic and the tricarboxylic-acid pathways to oxaloacetate and α-ketoglutarate, as well as a stimulation of amino-acid turnover. These effects were more pronounced at saturating irradiance.