NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO2

The effect of elevated atmospheric CO₂ on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton (¹H) nuclear magnetic resonance (NMR) imaging. Exposure of 24-d-old plants to atmospheric CO₂-enriched air at 650 cm³ m^?3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short-term drying-stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO₂ (350 m³ m^?3), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO₂ does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO₂ environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate.     

Niche differentiation and maintenance of genetic identity in cohabiting Eucalyptus species

Differences in niche utilization between two cohabiting eucalypt species (Eucalyptus signata and E. umbra ssp. umbra) on North Stradbroke Island, Qld., are documented, including differences in morphology, growth patterns, seasonality, insect attack and a three month difference in peak seasonal uptake of most essential elements. The significance of these niche differences in aiding the coexistence of competing eucalypt species is supported by results using recent theoretical models from niche theory. It is noted that the presence of significant niche complementarity amongst cohabiting pairs of eucalypts will place hybrid offspring at a disadvantage relative to homozygous strains. This phenomenon helps explain the scarcity or absence of hybrids in a number of communities where potentially interbreeding species of Eucalyptus coexist. Co-occurrence of species pairs which are capable of interbreeding will not be favored by environmental selection both because of the reduced production of homozygous offspring, and because of the reduced niche separation exhibited by taxonomically closely-related species. Such differences help explain the scarcity of co-occurrence of interbreeding pairs of species of Eucalyptus in relatively unperturbed natural communities.     

Factors affecting the assessment of resistance of potatoes to gangrene (Phoma exigua var. foveata)

Three experiments designed to elucidate the effects and interactions of different inoculation methods, inoculation positions, strains of Phoma exigua var. foveata and clones of potato tubers inoculated were analysed using as data dimensions of the lesions and a more general surface score. The assessment of susceptibility was affected by all these factors. The ranking of varieties for resistance altered considerably depending upon whether the surface area or the depth of lesions was considered. Derivation of more complex scores combining these measurements reduced the relative genetic component and hence would be of no value to potato breeders.     

Two New Subspecies of Herpetomonas muscarum (Leidy, 1856) Kent, 1880

SYNOPSIS. Herpetomonas muscarum muscarum n. subsp. was isolated from Musca domestica L. In culture at 20 C it assumed the opisthomastigote (up to 15%), double-flagellate and flagellate promastigote forms. At 30 C or with 4% urea added to cultures at 20 C, the proportion of opisthomastigotes was greater (up to 40%). In experimentally infected flies only transient infections, which included both opisthomastigotes and promastigotes, occurred. The promastigotes were 15–30 μ long and the kinetoplast was small and subspherical or transversely elongate. H. muscarum ingenoplastis n. subsp. was isolated from Phormia regina (Meigen). In culture at 20 C almost all individuals were double-flagellate promastigotes 20–40 μ long and less than 1% were opisthomastigotes. At 30 C or with added urea there was no increase in the proportion of opisthomastigotes and the cultures were not vigorous. In experimentally infected flies opisthomastigotes were 5–39% of the population depending on the part of the gut sampled. In all stages the kinetoplast was large (1.5–2.5 μ long) and tear-drop-shaped with the point directed posteriorly.
In artificially mixed cultures of H. m. muscarum and H. m. ingenoplastis the former predominated after a short time and eventually survived alone. A mixed culture that was about 98% H. m. muscarum was fed to Phormia regina and produced heavy pure infections of H. m. ingenoplastis , which lasted for 22 days with no indication of decline. No evidence of cyst formation was found in either subspecies.