Potassium-Ammonium Uptake Interactions in Tobacco Seedlings

Short-term (< 12 h) uptake experiments were conducted with6–7-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K⁺ andNH₄⁺. At equal solution concentrations (0.5 mol m^–3) netK⁺ uptake was inhibited 30–35% by NH₄⁺ and NH₄⁺ uptakewas decreased 9–24%. Removal of NH₄⁺ resulted in completerecovery in K⁺ uptake rate, but NH⁴⁺ uptake rate did not recoverwhen K⁺ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m^–3. The relative effectof K⁺-NH₄⁺ interactions was not altered when Cl- was replacedwith SO₄^2–, but the magnitudes of the uptake rates wereless in the absence of Cl-. The V_max for NH₄⁺ uptake was reducedfrom 128 to 105 µmol g^–1 dry wt. h^–1 in thepresence of 0.5 mol m^–3 K⁺ and the K_m for NH₄⁺ doubledfrom 12 to 27 mmol m^–3 in the presence of K⁺. The resultsof these K⁺-NH₄⁺ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K⁺ coupled to NH₄⁺influx via an antiporter cannot be ruled out as contributingto the decrease in net K⁺ uptake. Key words: Nicotiana tabacum, K⁺, NH₄⁺, Uptake interactions     

Experimental Histomoniasis in the Guinea Fowl,Numida meleagris*

Guinea fowl were inoculated rectally with Histomonas meleagridis to produce histomoniasis. The birds were infected readily by this unnatural route. Severe cecal involvement was frequent and long-lasting but liver lesions and death were rare. Turkeys given the same inoculum had high levels of liver involvement and mortality. Guinea fowl responded much less severely to infection with H. meleagridis when infected by a natural route (ingestion of a vector) rather than by rectal inoculation. Thus, naturally acquired infections with H. meleagridis appear to be of small consequence in the guinea fowl.     

Infectivity of Histomonas meleagridis of Cecal and Liver Origins Compared

SYNOPSIS. Turkey poults were inoculated rectally with 100, 1000, 10,000, or 100,000 Histomonas meleagridis from the ceca of a group of experimentally infected turkeys. Other poults were given the same numbers of histomonads from an infected liver from the same group of source birds, Comparisons of the incidence of infection, liver involvement, mortality, and average survival time following these inoculations showed that organisms of cecal origin were about 100 times more effective in producing histomoniasis than were organisms of liver origin. It is suggested that this difference in infectivity resulted from heavy losses of histomonads of liver origin that were due to various selective processes.     

The Middle Ear--Morphological Types in Amphibians and Reptiles

The middle ear regions of reptiles and amphibians frequentlyare grouped into morphological types on the basis of structuralresemblances. The arrays of animals resulting from such a groupinghave a fair degree of taxonomic continuity. The types in mostinstances include a "central" pattern, presumed to be primitive,and modifications that are considered to have been derived fromthe "central" type by evolutionary processes. Some understandingof phylogeny, thus, is a necessary precursor to the formationof the groups. This raises problems when, as is often the case,the groups based on ear structures are used as a basis for phylogeneticinterpretations. Among reptiles the theropsid-sauropsid caseis the best known. The principal morphological types are described and discussed.The middle ear, as a sound-transmitting apparatus and in itsassociations with the masticatory apparatus, is highly susceptibleto adaptive modifications. Some morphological types, such asthose in archosaurs and labyrinthodonts, are quite stable. Othersshow marked evolutionary diversity. The middle ear structures,hence, appear quite useful as phylogenetic indicators withinmorphological types but less so when relationships between typesare considered.     

Replication slippage may cause parallel evolution in the secondary structures of mitochondrial transfer RNAs

Presence of the dihydrouridine (D) stem in the mitochondrial cysteine tRNA is unusually variable among lepidosaurian reptiles. Phylogenetic and comparative analyses of cysteine tRNA gene sequences identify eight parallel losses of the D-stem, resulting in D-arm replacement loops. Sampling within the monophyletic Acrodonta provides no evidence for reversal. Slipped-strand mispairing of noncontiguous repeated sequences during replication or direct replication slippage can explain repeats observed within cysteine tRNAs that contain a D-arm replacement loop. These two mechanisms involving replication slippage can account for the loss of the cysteine tRNA D-stem in several lepidosaurian lineages, and may represent general mechanisms by which the secondary structures of mitochondrial tRNAs are altered.      

Effects of elevated atmospheric CO2 on fine root length and distribution in an oak-palmetto scrub ecosystem in central Florida

Atmospheric CO₂ concentration is rising and it has been suggested that a portion of the additional carbon is being sequestered in terrestrial vegetation and much of that in below-ground structures. The objective of the present study was to quantify the effects of elevated atmospheric CO₂ on fine root length and distribution with depth with minirhizotrons in an open-top chamber experiment in an oak-palmetto scrub ecosystem at Kennedy Space Centre, Florida, USA. Observations were made five times over a period of one and a half years in three ambient chambers (350 p.p.m. CO₂), three CO₂ enriched chambers (700 p.p.m. CO₂), and three unchambered plots. Greater root length densities were produced in the elevated CO₂ chambers (14.2 mm cm^?2) compared to the ambient chambers (8.7 mm cm^?2). More roots may presumably lead to more efficient acquisition of resources. Fine root abundance varied significantly with soil depth, and there appeared to be enhanced proliferation of fine roots near the surface (0–12 cm) and at greater depth (49–61 cm) in the elevated CO₂ chambers. The vertical root distribution pattern may be a response to availability of nutrients and water. More studies are needed to determine if increased root length under CO₂ enriched conditions actually results in greater sequestering of carbon below ground.     

cDNA cloning of a developmentally regulated hemocyanin subunit in the crustacean Cancer magister and phylogenetic analysis of the hemocyanin gene family

The complete cDNA sequence and protein reading frame of a developmentally regulated hemocyanin subunit in the Dungeness crab (Cancer magister) is presented. The protein sequence is aligned with 18 potentially homologous hemocyanin-type proteins displaying apparent sequence similarities. Functional domains are identified, and a comparison of predicted hydrophilicities, surface probabilities, and regional backbone flexibilities provides evidence for a remarkable degree of structural conservation among the proteins surveyed. Parsimony analysis of the protein sequence alignment identifies four monophyletic groups on the arthropodan branch of the hemocyanin gene tree: crustacean hemocyanins, insect hexamerins, chelicerate hemocyanins, and arthropodan prophenoloxidases. They form a monophyletic group relative to molluscan hemocyanins and nonarthropodan tyrosinases. Arthropodan prophenoloxidases, although functionally similar to tyrosinases, appear to belong to the arthropodan hexamer- type hemolymph proteins as opposed to molluscan hemocyanins and tyrosinases.      

APPLICATIONS OF SENSORY SCIENCE WITHIN THE TOBACCO INDUSTRY

Sensory testing of cigarette smoke presents some unique problems to the sensory specialist. This is due to a variety of reasons including the high degree of similarity between blended cigarettes and a high degree of variability between individual cigarettes. In the cigarette industry, a large effort has been placed on adapting and developing new methods of collecting and analyzing sensory-data on both flavorants and cigarette smoke. These methods include odor profiling and multidimensional scaling based on attributes and acceptability scales. In addition, extensive research has been conducted to determine the number of relevent dimensions to smoking and the types of changes that could affect consumer acceptance or purchase behavior.     

Histomonas wenrichi n. sp. (Mastigophora: Mastigamoebidae), a Nonpathogenic Parasite of Gallinaceous Birds

SYNOPSIS. A nonpathogenic histomonad, morphologically identical to that found in pheasants by Wenrich in 1943, is described as Histomonas wenrichi n. sp. Its dimensions are about 1.5 × those of H. meleagridis. It has 4 flagella instead of the 1 or 2 that characterize the latter species. It does not multiply in the host tissues nor produce visible responses to its presence there, and it does not exist as the clear "tissue form" that is common in active H. meleagridis infections.
Histomonas wenrichi n. sp. can be transmitted to turkeys, chickens, and pheasants by either rectal inoculation or by feeding embryonated eggs of Heterakis gallinarum grown in birds harboring the nonpathogenic histomonad in the ceca. Usually fewer than half the female heterakids so grown produce eggs capable of transmitting this histomonad, and a total of 200 to several thousand eggs from worms recovered from Histomonas -infected birds may be required to produce one Histomonas infection.
Histomonas wenrichi n. sp. has been propagated in more than 2000 chickens and turkeys over an 8-year period, during which time it has been transmitted by 18 generations of Heterakis. It has frequently been grown in birds in which H. meleagridis was also present, and upon reisolation it maintained all of its original characteristics. It has not yet been cultivated in vitro.