The Permeability of Ammonia, Methylamine and Ethylamine in the Charophyte Chara corallina (C. australis)

Ritchie, R. J. 1987. The permeability of ammonia, methylamineand ethylamine in the charophyte Chara corallina (C. australis).—J.exp. Bot. 38: 67–76 The permeabilities of the amines, ammonia (NH₃), methylamine(CH₃NH₂) and ethylamine (CH₃CH₂NH₂) in the giant-celled charophyteChara corallina (C. australis) R.Br. have been measured andcompared. The permeabilities were corrected for uptake fluxesof the amine cations. Based on net uptake rates, the permeabilityof ammonia was 6?4?0?93 µm s^–1 (n = 38). The permeabilitiesof methylamine and ethylamine were measured in net and exchangeflux experiments. The permeabilities of methylamine were notsignificantly different in net and exchange experiments, norto that of ammonia (P_methylamine = 6?0?0?49 µm s^–1(n = 44)). In net flux experiments the apparent permeabilityof ethylamine was slightly greater than that of ammonia andmethylamine (P_{ethylamine, net} = 8?4?1?2 µm s^–1 (n= 40)) but the permeability of ethylamine based on exchangeflux data was significantly higher (P_{ethylamine, exchange} =14?1?2 µm s^–1 (n = 20)). Methylamine can be validlyused as an ammonium analogue in permeability studies in Chara. The plasmalemma of Chara has acid and alkaline bands; littlediffusion of uncharged amines would occur across the acid bands.The actual permeability of amines across the alkaline bandsis probably about twice the values quoted above on a whole cellbasis i.e. the permeability of ammonia across the permeablepart of the plasmalemma is probably about 12 µm s^–1. Key words: Chara, permeability, ammonia, methylamine     

The Effect of Interleukin-2 on Parasitemia and Myocarditis in Experimental Chagas' Disease

Previous investigations showed that interleukin-2 (IL-2) administered in vivo into mice infected with Trypanosoma cruzi reduced levels of parasitemia and increased longevity. Present experiments examined the effect of administration of different doses of IL-2 at different times during infection in mice on parasitemia and histopathoiogy of heart tissue. Two different doses of IL-2 (1,500 or 10,000 U) given at 3 different times during infection were equivalent in reducing parasitemia. All of the IL-2 treated groups of mice had significantly lower numbers of circulating trypomastigotes as compared with controls not receiving this fymphokine. This IL-2 treatment of T . crazi-infected mice resulted also in lower numbers of pseudocysts in all 4 ventricular regions in the hearts. This was particularly evident in the more severely infected right ventricular wall; however, a similar decrease was not as apparent in the less severely infected left ventricular wall. The IL-2 treated, infected mice showed minimal or no effect in reducing inflammation of myocardial cells. However, the mildest inflammation of ventricular wall tended to occur in mice receiving IL-2 treatment either as a low dose (1,500 U) or a high dose (10,000 U) at 5, 7 and 9 days after infection as compared with mice treated later on. It was concluded that IL-2 treatment of infected mice produced a significant decrease in parasitemia and decreased infection of myocardial cells. Key words. Heart, histopathoiogy, inflammation, lymphokine, myocardial cells, pseudocyst, Trypanosoma cruzi .     

The Effects of Low Growth and Measurement Temperature on the Respiratory Properties of Five Temperate Species

Five temperate ruderal species, Epilobium glandulosum, Matricariamatricariodes, Melilotus alba, Sonchus asper and Taraxacum officinale,were grown under controlled conditions at both 10 °C and20 °C. Respiration was measured at 10 °C and 20 °C.Total dark respiration rates of plants grown at 10 °C wereconsistently higher than the rates of plants grown at 20 °C.This was due to greater respiratory activity along both thecytochrome (KCN-sensitive) and alternative (SHAM-sensitive)pathways in the cold grown plants. The capacity to use the alternativepathway was also greater in the 10 °C grown plants. Theincrease in the relative contribution of each pathway was speciesspecific. At a given growth temperature the activity of thealternative pathway varied little between measurements at 10°C and 20 °C. In contrast, the activity of the cytochromepathway was greater when measured at 20 °C than when itwas measured at 10 °C. The capacity of the alternative pathwaywas lower when measured at 10 °C. These results suggestthat the cytochrome pathway is more sensitive to temperaturestress than is the alternative pathway. Alternative pathway, cyanide resistance, cytochrome pathway, respiration, temperature     

Ethylene Biosynthesis and Xylogenesis in Lactuca Pith Explants Cultured In Vitro in the Presence of Auxin and Cytokinin: The Effect of Ethylene Precursors and Inhibitors

The possible involvement of ethylene in the induction of xylemdifferentiation was studied in lettuce (Lactuca saliva L. cv.Romaine) pith parenchyma explants. The addition of the ethyleneprecursors L-methionine (0.25 µM), S-adenosylmethionine(25 µM) and 1-aminocyclopropane-l-carboxylic acid (0.01µM), or the ethylene-releasing agent 2-chloroethylphosphonicacid (1.0 µM), to a standard IAA-kinetin-containing mediumenhanced xylogenesis compared to control explants cultured inthe absence of these compounds. In the presence of the ethyleneinhibitors aminoethoxyvinylglycine, Co(NO₃)₂ and AgNO₃, xylogenesiswas inhibited. Inhibition of xylogenesis by aminoethoxyvinylglycine(75 µM), Co(NO₃)₂ (50 µM) and AgNO₃ (6.0 µM)was reversed by exogenous 1-aminocyclopropane-l-carboxylic acid(0.01 µM), 2-chloroethylphosphonic acid (5.0 µM)and L-methionine (0.25 µM), respectively. Ethylene productionby explants cultured on media containing L-methionine or 1-aminocyclopropane-l-carboxylicacid was greater than the biosynthesis of ethylene by explantscultured in the absence of these compounds. The incorporationof 2-chloroethylphosphonic acid into the culture medium resultedin higher rates of ethylene production compared to explantscultured on the IAA-kinetin medium. The presence of either aminoethoxyvinylglycineor Co(NO₃)₂ inhibited ethylene production by explants culturedon the IAA-kinetin medium. The data support the hypothesis thatethylene plays a positive role in the initiation of xylem differentiation. Key words: Xylogenesis, Differentiation, Ethylene, IAA, Kinetin, Lactuca sativa     

Day and night feeding territoriality in Willets Catoptrophorus semipalmatus and Whimbrel Numenius phaeopus during the non-breeding season in the tropics

This study was carried out to determine whether or not, and under what conditions, Willets Catoptrophorus semipalmatus and Whimbrel Numenius phaeopus continue to defend and use their daytime feeding territories at night in a tropical environment. The study was conducted in coastal Venezuela by registering, by night and by day, the behaviour and the position of colour-marked and radio-tagged birds. Night observations were made with the use of a light intensifier.
In Willets, both territorial and non-territorial birds were observed. The use and defence of territories was observed only on sandy mud areas where Fiddler Crabs Uca cumulanta were plentiful; the soft mud sites were used only by non-territorial birds. All Whimbrel were territorial. Individuals of both species defending a given space during daytime continued to occupy and defend the same area during the night. The proportion of birds foraging at night was higher on moonlit than on moonless nights. Territorial defence involved alert postures, parallel walks, calls and the chasing of intruders. Agonistic encounters between Willets and Whimbrel and other species were rare. Willets were territorial at all states of the tide except when high tides flooded the territories. Tide had no effect on the time of feeding in Whimbrel. Moonlight was clearly the factor conditioning the occurrence of nocturnal foraging on territories by both species. Foraging strategies and the type of prey and substrata explain why the incidence of night foraging varied with moonlight in territorial Willets and Whimbrels and not in non-territorial individuals.     

Contrasted responses to carbohydrate limitation in tomato fruit at two stages of development

The metabolic consequences of long‐term carbohydrate depletion have been well documented in many sink organs but not extensively in fruit. Therefore, in the present study the response to sugar limitation in tomato fruit (Lycopersicon esculentum Mill.) was investigated at two developmental stages; during the cell division and cell expansion phases. First, the response in excised fruit cultured in vitro was characterized. Sugar depletion caused an arrest of growth and an exhaustion of carbon reserves. The proteins that were degraded and the nitrogen released was transiently stored as asparagine and glutamine in both developmental stages and also as γ ‐aminobutyric acid (GABA) in expanding fruit. Fruit at the cell division stage appeared to be more sensitive to sugar limitation. The response to sugar depletion was then characterized in fruit from plants submitted to extended darkness. In planta, the effects of sugar‐limitation were similar to those described in vitro but much more attenuated, especially in expanding fruit, which still accumulated dry matter. The expression of cell cycle genes, sugar‐ and nitrogen‐related genes was reduced by darkness. Only asparagine synthetase gene expression was induced in both dark‐treated fruit. Together the present data revealed that the effects of the carbon limitation are more pronounced in the youngest fruits as it is probably controlled by the relative sink strength of the fruit.     

Differentiating Migration and Dispersal Processes for Pond-Breeding Amphibians

Abstract Understanding the movement of animals is critical to many aspects of conservation such as spread of emerging disease, proliferation of invasive species, changes in land-use patterns, and responses to global climate change. Movement processes are especially important for amphibian management and conservation as species declines and extinctions worldwide become ever more apparent. To better integrate behavioral and ecological data on amphibian movements with our use of spatially explicit demographic models and guide effective conservation solutions, I present 1) a synopsis of the literature regarding behavior, ecology, and evolution of movement in pond-breeding amphibians possessing biphasic life cycles to distinguish between migration and dispersal processes, 2) a working hypothesis of juvenile-based dispersal, and 3) a discussion of conservation issues that follow from distinguishing the spatial and temporal movements of amphibians at different scales. I define amphibian migration as intrapopulational, round-trip movements toward and away from aquatic breeding sites. Population-level management, in general, can be focused on spatial scales of <1.0 km with attention focused on adult population and juveniles that remain near the natal wetland. I define amphibian dispersal as interpopulational, unidirectional movements from natal sites to other breeding sites. Metapopulation- or landscape-level management can be focused on movements among populations at spatial scales >1.0–10.0 km and on importance of terrestrial connectivity. The ultimate goal of conservation for amphibians should be long-term regional persistence by addressing management issues at both local and metapopulation scales.     

Long-term bird population studies in the United States

Long-term population studies of birds in the United States have been less species-oriented and more concept-oriented than in Britain. The demographics of North American species do not differ grossly from those of species elsewhere in the world, but polygamy has been relatively more frequently studied in U.S. species than elsewhere. Subjects that have been particularly explored in long-term studies in the United States include the determinants of cooperative breeding in birds, the effects of the spatial scale on what is learned, and correlates of regional and national declines in bird populations. Other areas of developing interest include the potential uses of monitoring data, the relative value of longitudinal and cross-sectional studies in analysing slow processes, and the significance of episodic events in shaping population patterns.     

Integrating Thermal Physiology and Ecology of Ectotherms: A Discussion of Approaches

An understanding of interactions between the thermal physiologyand ecology of ectotherms remains elusive, partly because informationon the relative performance of whole-animal physiological systemsat ecologically relevant body temperatures is limited. Afterdiscussing physiological systems that have direct links to ecology(e.g., growth, locomotor ability), we review analytical methodsof describing and comparing certain aspects of performance (includingoptimal temperature range, thermal performance breadth), applythese techniques in an example on the thermal sensitivity oflocomotion in frogs, and evaluate potential applications.     

Deer Carrying Capacity in Mid-Rotation Pine Plantations of Mississippi

ABSTRACT Herbicides, commonly used for vegetation management in intensively managed pine (Pinus spp.) forests of the southeastern United States, with and without fire, may alter availability of quality forage for white-tailed deer (Odocoileus virginianus; deer), an economically and socially important game species in North America. Because greater forage quality yields greater deer growth and productivity and intensively managed pine forests are common in the southeastern United States, forest managers would benefit from an understanding of fire and herbicide effects on forage availability to improve habitat conditions for deer. Therefore, we evaluated independent and combined effects of fire and herbicide (i.e., imazapyr) on forage biomass and deer nutritional carrying capacity (CC) on land owned and managed by Weyerhaeuser NR Company in east-central Mississippi, USA. We used a randomized complete block design of 6 pine plantations (blocks) divided into 4 10-ha treatment plots to each of which we randomly assigned a treatment (burn-only, herbicide-only, burn + herbicide, and control). We estimated biomass (kg/ha) of moderate- and high-use deer forage plants during July of 1999–2008, then estimated CC for diets to support either body maintenance (6% crude protein) or lactation (14% crude protein) with a nutritional constraints model. Herbaceous forages responded positively to fire and herbicide application. In most years, CC estimates for maintenance and lactation were greater in burn + herbicide than in controls. Maintenance-level CC was always greater in burn + herbicide than in controls, except at 1 year posttreatment. Burn + herbicide was 2.6–8.3 times greater (x̄ = 4.0) than control for lactation-level CC in 8 of 9 years posttreatment. We recommend fire and selective herbicides to increase high-quality deer forage in mid-rotation, intensively managed pine plantations.