Altitudinal changes in the incidence of crassulacean acid metabolism in vascular epiphytes and related life forms in Papua New Guinea

Summary The occurrence of Crassulacean acid metabolism (CAM), as judged from ¹³C values, was investigated in epiphytes and some related plant species at a series of sites covering the approximate altitudinal range of epiphytes in Papua New Guinea. Comprehensive collections were made at each site and the occurrence of water storage tissue and blade thickness was also determined. Some 26% of epiphytic orchids from a lowland rainforest (2–300 m.a.s.l) showed ¹³C values typical of obligate CAM and possessed leaves thicker than 1 mm. A second group of orchids, mostly with succulent leaves, possessed intermediate ¹³C values between -23 and -26% and accounted for 25% of the total species number. Some species of this group may exhibit weak CAM or be facultative CAM plants. The remainder of the lowland rainforest species appeared to be C₃ plants with ¹³C values between -28 and -35%. and generally possessed thin leaves. Obligate CAM species of orchids from a lower montane rainforest (1175 m.a.s.l) comprised 26% of the species total and mostly possessed thick leaves. The remainder of the species were generally thin-leaved with ¹³C values between -26 and -35%. largely indicative of C₃ photosynthesis. Orchids with intermediate ¹³C values were not found in the lower montane rainforest. Obligate CAM appeared to be lacking in highland epiphytes from an upper montane rainforest and subalpine rainforest (2600–3600 m.a.s.l). However the fern, Microsorium cromwellii had a ¹³C value of -21.28%. suggesting some measure of CAM activity. Other highland ferns and orchids showed more negative °¹³C values, up to-33%., typical of C₃ photosynthesis. The highland epiphytic orchids possessed a greater mean leaf thickness than their lowland C₃ counterparts due to the frequent occurrence of water storage tissue located on the adaxial side of the leaf. It is suggested that low daytime temperatures in the highland microhabitats is a major factor in explaining the absence of CAM. The increased frequency of water storage tissue in highland epiphytes may be an adaptation to periodic water stress events in the dry season and/or an adaptation to increased levels of UV light in the tropicalpine environment.     

The biology of Brachycentrus subnubilus Curtis (Trichoptera) in the River Frome,Dorset

Aspects of life-history, oviposition and microdistribution within beds of Ranunculus penicillatus var. calcareus (R. W. Butcher) C.D.K. Cook are considered. Brachycentrus subnubilus Curtis has one generation each year, with five larval instars. Larvae favour sites beneath the weedbeds for most of the year, migrating to more exposed areas in the spring to pupate. Pupation, emergence, oviposition and eclosion are completed in just over two months. Eggs are usually laid on submerged marginal vegetation but any semi-submerged object may be utilized. Larvae appear to disperse mainly as first instars; in this they are likely to be seriously affected by weedcutting activities. Initial development is rapid to fourth instar. Larvae overwinter as fifth instars. Sex ratios show a predominance of males.     

Storage carbohydrate production and overwintering strategy in a winter-green tussock grass on South Georgia (Sub Antarctic)

Summary Water-soluble and ethanol-soluble carbohydrates were extracted from leaves, shoots, roots, rhizomes and flowers ofParodiochloa flabellata (Lam.) Rasp. (=Poa flabellata (Lam.) Hook f.) throughout a growing season. Very high levels of soluble carbohydrates were found in the shoot, comprising up to 71% of the shoot dry weight. There was no significant storage in the rhizome. It is suggested that the production of storage fructans with a degree of polymerization greater than 14, rather than oligosaccharides or starch, may be related to the cold environment. Relationships between the onset of senescence and levels of fructans suggest that recovery of sugars from dying tissue is high. The sugar reserves together with preformation of the flowers should ensure production of seed however poor the summer or long the winter might be. The high levels of fructans may partly inhibit growth but may also offer some degree of freezing resistance.     

Bactericidal activity of peroxynitrite.

Peroxynitrite is a strong oxidant formed by macrophages and potentially by other cells that produce nitric oxide and superoxide. Peroxynitrite was highly bactericidal, killing Escherichia coli in direct proportion to its concentration with an LD50 of 250 microM at 37 degrees C in potassium phosphate, pH 7.4. The apparent bactericidal activity of a given concentration peroxynitrite at acidic pH was less than that at neutral and alkaline pH. However, after taking the rapid pH-dependent decomposition of peroxynitrite into account, the rate of the killing was not significantly different at pH 5 compared to pH 7.4. Metal chelators did not decrease peroxynitrite-mediated killing, indicating that exogenous transition metals were not required for toxicity. The hydroxyl radical scavengers mannitol, ethanol, and benzoate did not significantly affect toxicity while dimethyl sulfoxide enhanced peroxynitrite-mediated killing. Dimethyl sulfoxide is a more efficient hydroxyl radical scavenger than the other three scavengers and increased the formation of nitrogen dioxide from peroxynitrite. In the presence of 100 mM dimethyl sulfoxide, 60.0 +/- 0.3 microM nitrogen dioxide was formed from 250 microM peroxynitrite as compared to 2.0 +/- 0.1 microM in buffer alone. Thus, formation of nitrogen dioxide may have enhanced the toxicity of peroxynitrite decomposing in the presence of dimethyl sulfoxide.     

Correlation between serum ionised calcium and serum albumin concentrations in two hospital populations.

One quarter of 172 patients from two hospitals with no obvious disturbances of calcium homeostasis and with total serum calcium concentrations that were normal after adjustment for albumin concentration had low serum ionised calcium concentrations. The low values were not due to changes in pH but were associated with hypoalbuminaemia. Significant positive regressions of ionised calcium on albumin concentration were observed in patients from both hospitals and also in 48 healthy laboratory staff. Because the regressions did not differ between patients and healthy subjects the low ionised calcium values associated with hypoalbuminaemia are unlikely to have been of pathological importance. These findings indicate that interpreting serum ionised calcium concentrations in patients with a reduced serum albumin concentration on the basis of a reference range determined in subjects with a normal serum albumin concentration may be clinically misleading.     

Merremia discoidesperma: Its taxonomy and capacity of its seeds for ocean drifting

Merremia discoidesperma (Donn. Sm.) O’Donell (Mary’s-bean) is a rarely collected and inadequately described high climbing woody liana of Chiapas, Mexico; Guatemala; Costa Rica; Hispaniola; and Cuba. There is only one record of this species being cultivated and this from Guanajuato, Mexico in 1894, though seeds are used in folk remedies. These seeds are topographically unlike other known convolvulaceous seeds, thus permitting their positive identification. Because seeds remain buoyant for more than three years in seawater, those produced in the Caribbean and Atlantic drainage region may be transported by the Gulf Stream System as far north as the Norwegian coast, a distance of about 9,500 km. Seeds produced in the Pacific drainage region from Chiapas, Mexico south to Costa Rica may be transported by the North Pacific Equatorial Current as far west as Wotho Atoll in the Marshall Islands, a distance of about 11,000 km. Records of drifting and subsequent stranding of these and other tropical New World disseminules are supported by drift bottle studies and drift debris records in the Atlantic Ocean. In the Pacific Ocean region distribution of stranded Mary’s-bean seeds is supported by a similar distribution of New World pumice. There is an indication in the literature that Mary’s-bean seeds may drift to the Philippines. The record from Wotho Atoll to Norway constitutes the widest drift range of any seed or fruit which has been documented. Other tropical disseminules may drift as far or farther, but their origins cannot be ascertained with certainty. The plant is described, its synonyms listed, and its distribution as well as the distribution of its stranded seeds recorded.     

Functional differences among nonerythroid anion exchangers expressed in a transfected human cell line

A new transient expression system has been developed to investigate the function of anion exchangers in vivo. Human 293 cells were cotransfected with AE2 or AE3 cDNA together with a plasmid encoding a cell surface marker protein. Staining of the cells with antibody directed against a cell surface epitope present in the marker protein permitted the detection of cells expressing functional anion exchangers. Intracellular pH (pHi) recording in individual transfectants loaded with the fluorescent pHi indicator, 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein, was used to determine the flux of HCO3- as a measure of Cl-/HCO3- exchange activity. Cells expressing either anion exchanger displayed significantly enhanced Cl-/HCO3- exchange activity compared with controls expressing only the marker. Transfection with either anion exchanger or with control plasmid resulted in altered intrinsic buffering capacity profiles compared with untransfected controls. Expression of either AE2 or AE3 did not result in changes in resting pHi. The activities of both AE2 and AE3 were stimulated at alkaline pHi, suggesting that an internal protonation site in AE2 and AE3 may regulate their activities. Both exchangers were inhibited reversibly and irreversibly by the anion 4,4'-diisothiocyanostilbene-2,2'-disulfonate with IC50 values of 142 and 0.43 microM for AE2 and AE3, respectively. These data indicate that structural differences in these highly conserved anion exchangers give rise to differences in affinities at the external anion binding site.     

Cloning and linkage analysis of Neisseria gonorrhoeae DNA methyltransferases.

We have cloned DNA methyltransferases (MTases) from various strains of Neisseria gonorrhoeae. Each of these clones represents a single specificity, indicating that the multiple gonococcal MTase specificities are encoded by monospecific MTases. The DNAs of five strains (FA5100, F62, MS11, Pgh3-2, and WR302) were digested with NheI, SpeI, or NheI plus SpeI and subjected to pulsed-field gel electrophoresis. The DNA MTase clones were used to probe Southern blots of these pulsed-field gels to determine whether the MTase genes are linked and whether there are strain-to-strain differences. The results indicate that none of these genes are closely linked, but variable hybridization patterns indicate that there exist restriction fragment length polymorphisms between the strains tested. Most of the chromosomal regions containing these restriction fragment length polymorphisms are clustered in regions containing gonococcal genes known or suspected to antigenically vary via genetic recombination.     

A note on the isolation and enumeration of Gram positive cocci from marine and estuarine waters

Ninety-two percent of Gram positive cocci detected in estuarine and marine surface waters were identified as Staphylococcus spp. Micrococcus and Streptococcus spp. were rarely isolated from seawater, except at dump site stations located in the Puerto Rico Trench area of the Atlantic Ocean, where they were present in unusually large numbers. Staphylococci were present in greatest abundance near land, but were also found in open ocean surface waters in low, but relatively constant, numbers. Staphylococcus epidermidis , or strains related to Staph. hominis , were present in all samples. Staphylococci from surface water samples collected at the Puerto Rico Trench dump site degraded a wide range of compounds. It is considered that these cocci were derived from the wastes dumped, as very few were found in unpolluted marine waters and in those cases in which stimulatory factors, such as disposal of wastes, do not play a role, Gram positive cocci will not be recovered unless large volumes of water are filtered. The Gram positive cocci are present in very low numbers in natural seawater of the open ocean and, therefore, are commonly overlooked. The significance of these bacteria in the nutrient cycles of the sea remains to be elucidated. Documentation of a widespread occurrence of Gram positive cocci in North Eastern Atlantic seawater is provided.