Immunologic Analysis by Gel Diffusion Technics of the Effects of Prolonged Cultivation on Trichomonas gallinae*

SYNOPSIS. Antisera were developed in rabbits against 3 axenic lines of Trichomonas gallinae: JB(VI), the 6th isolate of the very virulent Jones' Barn strain, which was kept frozen in liquid nitrogen and had its full pathogenicity for pigeons when it was employed for immunization; JB(VI)C, a substrain derived from JB(VI), but attenuated during continuous in vitro cultivation for 1 year; and JB(V)C, a substrain of the 5th isolate of the Jones' Barn strain attenuated during continuous in vitro cultivation for over 3 years. All antisera were reacted on gel diffusion slides with varying concentrations of homologous and heterologous antigens. Two groups of precipitin bands, arbitrarily labeled A and B, were seen on the slides. Analysis of these bands revealed the common genetic makeup of the 3 trichomonad lines with respect to the group A bands. However, the group B antigenic system was strong in the attenuated JB(VI)C and JB(V)C substrains, and very weak in the fully pathogenic JB(VI) strain. These differences are discussed in the light of their possible relationship to pathogenicity.     

Rearing temperature influences flavivirus vector competence of mosquitoes

Culex annulirostris Skuse mosquitoes (Brisbane strain) were reared at 20 degrees C or 27 degrees C and the adult females were experimentally infected by feeding Murray Valley encephalitis virus (MVE). They were then maintained (a) in the insectary at 20 degrees C, after rearing at either 20 degrees C or 27 degrees C; (b) at ambient outdoor temperatures, range 12.2-28.9 degrees C, mean 19.6 degrees C; or (c) at 27 degrees C after rearing at 27 degrees C. There was no significant difference in rates of MVE infection or transmission when mosquitoes were reared and maintained constantly at 20 degrees C or 27 degrees C. However, for females kept at reduced temperature (i.e. mean = 19.6 degrees C or 20 degrees C after rearing at 27 degrees C), the infection and transmission rates of MVE were significantly reduced (2 x 8 replicates). This investigation illustrates that vector competence is depressed by decreasing temperatures for adult mosquitoes compared with those they experienced during development. Similar patterns were evident with previously published work on Japanese and St Louis encephalitis, dengue and yellow fever. The process appears to be reversible, i.e. increased temperature raises virus infection and transmission rates. It is concluded that, without incubation at warmer temperatures, flavivirus recovery from overwintering mosquitoes will be negatively biased.     

Phytoplankton nutrient limitation in Colorado mountain lakes

SUMMARY. 1. Limiting nutrients for phytoplankton were studied experimentally in eight mountain lakes of central Colorado between May and November of 1984.
2. Five categories of phytoplankton limitation were identified: no limitation, N limitation, P limitation, concurrent limitation (stimulation only by simultaneous additions of N and P), and reciprocal limitation (stimulation by addition of either N or P). The phytoplankton communities of three lakes were primarily N-limited, one was primarily phosphorus-limited, and four showed primarily combined limitation (concurrent or reciprocal). Switching between categories of limitation was also observed within lakes. Nitrogen was the most frequently limiting nutrient; N, either alone or in combination with P, accounted for 79% of all observed instances of limitation.
3. Nine indices were tested for effectiveness in predicting phytoplankton limitation by N and P. The best indices for discriminating all limitations were ratios of dissolved inorganic N: total P (84% accuracy) and dissolved inorganic N:total dissolved P (80% accuracy). The effectiveness of these indices may be explained by the degree to which they represent N and P fractions actually available to the phytoplankton.     

The Effects of Temperature on 86Rb Uptake by Two Species of Chlamydomonas (Chlorophyta, Chlorophyceae)

⁸⁶Rb uptake was examined in two species of unicellular greenalgae, Chlamydomonas nivalis isolated from snow, and a cellwall-less mutant of the temperate freshwater Chlamydomonas reinhardii.In C. reinhardii cells grown at 20°C and cooled rapidlyto 0°C, ⁸⁶Rb uptake was abolished. Cells cooled rapidlyto –5°C in the absence of ice accumulated ⁸⁶Rb veryrapidly but the time course of this uptake suggested non-selectiveaccumulation through a damaged plasmalemma. Cells grown at 8°Cwere viable, able to divide and motile; they showed no signsof cold-shock and ⁸⁶Rb uptake, albeit slow, was measurable at–5°C in the absence of extracellular ice. Cells ofC. nivalis grown at 20°C were damaged at sub-zero temperaturesalthough they did show an enhanced ⁸⁶Rb uptake at 0°C. Cellsgrown at 5°C were able to accumulate ⁸⁶Rb from media undercooledto -5°C in the absence of extracellular ice, and again showedenhanced uptake at 0°C. The process of acclimation to lowtemperature appears to differ in the two species. Key words: Chlamydomonas, temperature, ⁸⁶Rb uptake, membrane     

Effect of Localized Placement of Nutrients on Root Competition in Self-thinning Populations

The hypothesis that increased root competition can lower theslope and/or intercept of the self-thinning line traversed byplant populations was tested using localized placement of nutrientsto increase root competition. Localized placement of nutrientswill result in increased root competition, if average inter-rootdistances are reduced, and if nutrients are in limiting supply.It was predicted that high-density, nutrient-limited populationsof Ocimum basilicum L. grown with localized placement of nutrientswould self-thin along a lower biomass–density line thannon-localized controls. This was tested at two fertility levelson a soil-based potting medium in expt 1, and at one fertilitylevel on washed sand in expt 2. Localized placement of nutrients significantly reduced the elevation(intercept) of the self-thinning line for both shoot and rootbiomass in expt 2. In expt 1, at the higher-fertility level,localized placement of nutrients had no significant effect;at the lower fertility level, localization had no significanteffect on thinning lines for shoot biomass, and resulted ina zero slope of the thinning line for root biomass. Canopy-based models of self-thinning failed to account for thereduction in the thinning-line intercept observed in expt 2.In both experiments, localized placement of nutrients resultedin a higher proportion of total root length being located inthe localization zone, which would result in a reduction inthe average inter-root distance. This would intensify root competitionunder conditions of nutrient limitation. The hypothesis thatintensified root competition would lower the self-thinning lineis supported by the results of expt 2. Localized placement of nutrients; root competition; shoot competition; root–shoot allocation; self-thinning; Ocimum basilicum ; sweet basil