Cytometric quantification of nitrate reductase by immunolabeling in the marine diatom Skeletonema costatum.

BACKGROUND: The uptake of nitrate by phytoplankton is a central issue in biological oceanography due to its importance to primary production and vertical flux of biogenic carbon. Nitrate reductase catalyzes the first step of nitrate assimilation, the reduction of NO(3) to NO(2). A cytometric protocol to detect and quantify relative changes in nitrate reductase (NR) protein content of the marine centric diatom Skeletonema costatum is presented. METHODS: Immunolabeling of NR protein was achieved with polyclonal antibodies raised against S.costatum NR. Antisera specific to a NR protein subunit and to a NR polypeptide sequence were compared, and cytometric results of NR protein abundance were related to Western analyses. Changes in cellular NR abundance and activity were followed during an upwelling simulation experiment in which S. costatum was exposed to a shift from ammonia to nitrate as major nitrogen source. RESULTS: NR protein could be detected in NO(3)-grown cells and at extremely low levels hardly discernible by Western Blot densiometry in NH(4)-grown cells. The protocol allowed observation of early stages of NR induction during an upwelling simulation. NR abundance increased after the nutrient shift to reach a new physiological "steady-state" 96 hrs later. NR activity exhibited diel variation with maxima at mid-day. NR abundance as estimated by both flow cytometry and Western analysis exhibited a hyperbolic relationship to NR activity. This pattern suggests post-translational activation of NR protein. CONCLUSIONS: The presented protocol allows the differentiation of NH(4)- versus NO(3)-grown algae as well as the monitoring of early stages in the induction of nitrate assimilatory capacities.

Impacts of CO2 Enrichment on Productivity and Light Requirements of Eelgrass.

Seagrasses, although well adapted for submerged existence, are CO2-limited and photosynthetically inefficient in seawater. This leads to high light requirements for growth and survival and makes seagrasses vulnerable to light limitation. We explored the long-term impact of increased CO2 availability on light requirements, productivity, and C allocation in eelgrass (Zostera marina L.). Enrichment of seawater CO2 increased photosynthesis 3-fold, but had no long-term impact on respiration. By tripling the rate of light-saturated photosynthesis, CO2 enrichment reduced the daily period of irradiance-saturated photosynthesis (Hsat) that is required for the maintenance of positive whole-plant C balance from 7 to 2.7 h, allowing plants maintained under 4 h of Hsat to perform like plants growing in unenriched seawater with 12 h of Hsat. Eelgrass grown under 4 h of Hsat without added CO2 consumed internal C reserves as photosynthesis rates and chlorophyll levels dropped. Growth ceased after 30 d. Leaf photosynthesis, respiration, chlorophyll, and sucrose-phosphate synthase activity of CO2-enriched plants showed no acclimation to prolonged enrichment. Thus, the CO2-stimulated improvement in photosynthesis reduced light requirements in the long term, suggesting that globally increasing CO2 may enhance seagrass survival in eutrophic coastal waters, where populations have been devastated by algal proliferation and reduced water-column light transparency.

Carbon Partitioning in Eelgrass (Regulation by Photosynthesis and the Response to Daily Light-Dark Cycles).

Diel variations in rates of C export, sucrose-phosphate synthase (SPS) and sucrose synthase (SS) activity, and C reserves were investigated in Zostera marina L. (eelgrass) to elucidate the environmental regulation of sucrose formation and partitioning in this ecologically important species. Rates of C flux and SPS activity increased with leaf age, consistent with the ontogenic transition from sink to source status. Rates of C export and photosynthesis were low but quantitatively consistent with those of many terrestrial plant species. The Vmax activity of SPS approached that of maize, but substrate-limited rates were 20 to 25% of Vmax, indicating a large pool of inactive SPS. SPS was unresponsive to the day/night transition or to a 3-fold increase in photosynthesis generated by high [CO2] and showed little sensitivity to inorganic phosphate. Consequently, regulation of eelgrass SPS appeared similar to starch- rather than to sugar-accumulating species even though eelgrass accumulates sucrose. Leaf [sucrose] was constant and high throughout the diel cycle, which may contribute to the down-regulation of SPS. Root sucrose synthase activity was high but showed no response to nocturnal anoxia. Root [sucrose] also showed no diel cycle. The temporal stability of [sucrose] confers an ability for eelgrass to buffer the effects of prolonged light limitation that may be key to its survival and ecological success in environments subject to periods of extreme light limitation and chaotic daily variation in light availability.

Assessment of genetic diversity of seagrass populations using DNA fingerprinting: implications for population stability and management.

Populations of the temperate seagrass, Zostera marina L. (eelgrass), often exist as discontinuous beds in estuaries, harbors, and bays where they can reproduce sexually or vegetatively through clonal propagation. We examined the genetic structure of three geographically and morphologically distinct populations from central California (Elkhorn Slough, Tomales Bay, and Del Monte Beach), using multilocus restriction fragment length polymorphisms (DNA fingerprints). Within-population genetic similarity (Sw) values for the three eelgrass populations ranged from 0.44 to 0.68. The Tomales Bay population located in an undisturbed, littoral site possessed a within-population genetic similarity (Sw = 0.44) that was significantly lower than those of the other two populations. Cluster analysis identified genetic substructure in only the undisturbed subtidal population (Del Monte Beach). Between-population similarity values (Sb) for all pairwise comparisons ranged from 0.47 to 0.51. The three eelgrass populations show significantly less between locale genetic similarity than found within populations, indicating that gene flow is restricted between locales even though two of the populations are separated by only 30 km. The study demonstrates that (i) natural populations of Z. marina from both disturbed and undisturbed habitats possess high genetic diversity and are not primarily clonal, (ii) gene flow is restricted even between populations in close proximity, (iii) an intertidal population from a highly disturbed habital shows much lower genetic diversity than an intertidal population from an undisturbed site, and (iv) DNA fingerprinting techniques can be exploited to understand gene flow and population genetic structure in Z. marina, a widespread and ecologically important species, and as such are relevant to the management of this coastal resource.

Dihydroergotamine/heparin in the prevention of deep-vein thrombosis after total hip replacement. A controlled, prospective, randomized multicenter trial.

In a randomized, double-blind, placebo-controlled multicenter trial, the efficacy and safety of dihydroergotamine mesylate/heparin sodium as a prophylactic agent for deep-vein thrombosis were evaluated in 148 patients who were forty years old or more and who underwent total hip replacement. The incidence of venographically proved postoperative deep-vein thrombosis was 52 per cent in the placebo group and 25 per cent in the dihydroergotamine mesylate/heparin sodium group (p = 0.002). Proximal thrombi developed in only 5 per cent and extensive thrombi, in only 10 per cent of the patients who received dihydroergotamine mesylate/heparin sodium. In contrast, proximal thrombi and extensive thrombi developed in 19 and 25 per cent, respectively, of the patients in the placebo group (p less than 0.05). Adverse reactions in the two groups did not differ significantly: in the treatment group they consisted primarily of hematoma at the site of injection (9 per cent), hematoma at the wound (5 per cent), and excessive postoperative bleeding, and in the placebo group there was hematoma at the site of injection (3 per cent). It was concluded that the combination agent dihydroergotamine mesylate/heparin sodium was effective and safe prophylaxis against deep-vein thrombosis for the patients who underwent total hip replacement in this study.

In vitro steroid secretion by intact bovine ovarian follicles in a superfusion system.

A superfusion system for single intact follicles is described. Bovine follicles were superfused for 5 to 10 hours. Progesterone and testosterone secretion was stable after an adaptation period of 150 min. A 5-minute stimulation with hCG resulted in a 2-fold increase in progesterone secretion. Superfusion for 450 minutes of 3 small follicles of similar size and in the same ovary next to each other showed different secretion patterns of progesterone and testosterone. Superfusion for 150 minutes of follicles obtained from 2 pairs of ovaries showed that follicular size is not a sufficient criterion to predict the progesterone and testosterone secretion pattern. Closeness of follicles (big or small) to a corpus luteum did not impair their ability to secrete progesterone and testosterone. It is concluded that a superfusion system as has been described in this report is an effective and desirable method to study the physiology and pathophysiology of single intact follicles.

Methemoglobinemia from overdose of phenazopyridine hydrochloride.

A case of severe methemoglobinemia and hemolytic anemia following ingestion of 5.6 gm of phenazopyridine with suicidal intent by a 16-year-old woman was successfully treated with intravenous methylene blue. Methemoglobinemia was suspected in this patient because of her intense central cyanosis, chocolate-colored blood, and minimal dyspnea. The patient's peripheral blood smear exhibited "bite cells." To the best of our knowledge, this is only the third such case reported in the literature. The pathophysiology, diagnosis, and therapy are reviewed.