Proton Fluxes and the Activity of a Stelar Proton Pump in Onion Roots

The xylem vessels of excised adventitious roots of onion, Alliumcepa, were perfused with unbuffered nutrient solution adjustedinitially to either pH 9·3 or 3·9; the pH of thesolution after passage through the xylem, at rates not lessthan 2 xylem volume changes min^–1, was close to pH 6·5in both instances. The flux of H⁺ across the xylem/symplastboundary into mildly alkaline, phosphate-buffered solutionsperfusing the vessels could be increased greatly with increasingbuffer strength, up to a maximum value between 0·5–1·0pmol H⁺ mm^–2 s^–1. The apparent neutralization ofacidic malic acid buffers had a slightly lower maximum capacity,equivalent to –0·3 to –0·5 pmol H⁺mm^–2 s^–1. The addition of 5·0 pmol m^–3fusicoccin (FC) to the xylem perfusion solution stimulated theentry of H⁺ into the xylem; in unbuffered perfusion solutionsthe pH fell to pH 3·6 after a lag of 25–35 min.FC additions to phosphate-buffered solutions also stimulatedthe H⁺ flux to an extent similar to that in unbuffered solution,viz. 0·2–0·4 pmol mm^–2 s^–1. The release of K⁺ (³⁶Rb-labelled) into xylem sap transientlyincreased as the [K⁺] in weakly buffered perfusion solutionswas raised stepwise; a very marked increase being seen whenthe concentration was raised to 100 mol m^–3 from 40 molm^–3. The addition of 5·0 mmol m^–3 FC to theperfusing solution containing 100 mol m^–3 K⁺ rapidly decreasedthe K⁺ flux to the xylem as the H⁺ flux increased. Fusicoccinalso inhibited the flux of K⁺ into unbuffered perfusion solutionsbut the effect appeared reversible. Addition of 10 mmol m^–3abscisic acid (ABA) to the perfusion solution quickly producedtransient increases in both K⁺ and H⁺ fluxes into the xylem.In this and other experiments using weakly phosphate-bufferedperfusing solutions, H⁺ fluxes were comparable in size to thoseof K⁺ The results are consistent with the idea that the stele of onionroots contains a proton trarislocating ATPase whose activityresponds to the pH of the xylem sap. It is evident that theactivity of the proton secreting and proton neutralizing mechanismsin the xylem parenchyma control the movement of other ions acrossthe xylem/symplast boundary. Key words: Xylem perfusion, fusicoccin, abscisic acid, pH gradient     

Local population differences in emergence of cabbage root flies from south-west Lancashire: implications for pest forecasting and population divergence

ABSTRACT.

• 1 Emergence of cabbage root fly, Delia radicum (L.), from overwintering populations of puparia collected from twenty-one sites in south-west Lancashire, was extremely variable.
• 2 The patterns of emergence indicated that there were two extreme biotypes, one with early- and the other with late-emerging flies. There was also evidence of an intermediate biotype, tending more to early than to late emergence.
• 3 This gradient of biotypes, or clinal divergence, was maintained by populations breeding at different times and by females mating close to their sites of emergence. Non-dispersive females then perpetuated their genotype within their own locality.
• 4 The time of emergence was not obviously associated with the type of host-crop on which larvae had developed.
• 5 The late-emerging biotype was most prevalent around Halsall. The minimum distance between populations of the late- and the early-emerging biotypes was 16 km. 20 km south-east from Halsall only half of the fly population was early-emerging, possibly a result of a displacement of the Halsall biotype by the prevailing NW wind.
• 6 Regional-based forecasts will need to take into account the emergence characteristics of the populations to predict the peak periods of cabbage root fly activity adequately in south-west Lancashire and other areas where emergence patterns differ.

     

New Fibrous Long Spacing Form of Collagen

PRECIPITATION of collagen from solution in the presence of chondroitin sulphates (or certain other glycosaminoglycans), followed by dialysis against water, leads to the formation of the fibrous long spacing (FLS) polymorphic form of collagen. Electron microscopy shows this to consist of banded fibrils with a periodicity in the range 1200–2400 Å and a symmetric intraperiod structure, in contrast to the 600–700 Å periodicity and polarized fine structure characteristic of native collagen fibrils. FLS was originally reported by Highberger et al.^1–3 and has been observed in three principal modifications, FLS I, FLS II and FLS III, differing in periodicity and arrangement of dense bands^4–6. This letter reports a new form of FLS, denoted FLS IV.     

Biochemical Comparison of Some Classical Tetrahymena pyriformis and T. vorax Strains*

SYNOPSIS. The classical Tetrahymena pyriformis and T. vorax strains have been classified in antigenic subgroups based on immobilization and agar double diffusion in the presence of specific antisera. The present study utilized disc electrophoresis of proteins and lactate dehydrogenase isozymes for comparison of 11 strains. In agreement with similarities reported for agar diffusion data, close electrophoretic relationships were observed between strains GL and H, and V₂ and W with aniline black staining. Altho LDH isozyme production was more variable and related to cultural growth phase, similarities were recognized between GL and H, and F and PR.     

Range of Variation in the Somatic Infraciliature and Contractile Vacuole Pores of Tetrahymena pyriformis

SYNOPSIS. Meridian ranges and contractile vacuole pore patterns were determined for 36 strains of Tetrahymena pyriformis, including most of the “classic” amicronucleate and micronucleate strains used by many investigators, plus a dozen other strains not previously characterized with respect to these two morphological features. Uniform axenic culturing and staining techniques were employed. Meridian ranges and modes are analyzed with strain-by-strain comparisons to the reports of previous investigators. The overall inclusive range of the 36 strains was 15–25 meridians. Modes for individual strains varied from 16 to 23. Broader ranges and, especially, higher modes and higher limits are recorded than those reported by Corliss (1953) for strains grown in bacterized hay cultures. Two postoral meridians are characteristic, although a single individual having only one and a few having three postorals were observed. Three postorals were found only in those strains having the higher number of total meridians. A few individuals, showing an anterior half or a posterior half of a bipolar meridian missing, indicate a possible explanation of how a single dividing individual could produce a proter and an opisthe differing in the total number of meridians. Meridian ranges of individual strains do not overlap each other in all cases, but they do constitute a progressively overlapping series which does not warrant taxonomic separation of strains at either extreme from each other. Contractile vacuole pores varied from 1 to 3, with 2 pores (1 each in meridians 5 and 6) being characteristic of 22 of the strains. The 2-pore 6-7 pattern was modal for 8 of the strains. Presence of 3 pores (in 5, 6 and 7) was typical of only 2 strains, but 3 pores were found occasionally. Another pattern of 3 pores (in 6, 7 and 8) was observed occasionally in 10 strains. Double pores (in 6 and 7 or 7 and 8) and the triple pore patterns were observed only in the strains having the highest total number of meridians. These variations are not considered adequate justification for taxonomic separation. Strains Ki and Aq are affirmed to be T. pyriformis. Strains V¹ PP and V, formerly regarded as strains of T. vorax, are considered to be T. pyriformis, supporting the view of Shaw and Williams (1963).     

Identification of predominant environmental factors structuring stream macroinvertebrate communities within a large agricultural catchment

• 1 Patterns of macroinvertebrate community composition were examined in streams within a 40000-km² catchment in central Michigan, U.S.A., to identify the major environmental gradients influencing community variation. Agriculture and associated clay and sandy soils predominated in much of the region.
• 2 Eighty macroinvertebrate taxa were collected from stream surveys conducted during May and August 1990. Community composition varied primarily by the proportions of Plecoptera and Ephemeroptera. Benthic communities from the heaviest agricultural zones were most different from those at other sites.
• 3 Chemical composition among the sites varied most in relation to nutrients (NH₃, NO3, PO₄). Other parameters were relatively similar. Physical characteristics of the sites were scored in six habitat categories: (i) substrate characteristics, (ii) instream cover, (iii) channel morphology, (iv) riparian zone and stream-bank conditions, (v) riffle/run quality, (vi) pool quality. Most physical habitat scores were lowest in the intense agriculture zones.
• 4 The relative importance of physical and chemical variables in explaining variation in macroinvertebrate communities was quantified using canonical correspondence analysis. Substrate characteristics were most important in both surveys. Significant correlations (P<0.05 and P<0.10) were observed between substrate quality and total numbers of Ephemeropteran, Plecopteran, and Trichopteran taxa. These relationships reflected correlations from sites in the clay soil-type region (P<0.01 and P<0.10) which contrasted with non-significant results from the less impacted, sandy soil-type region.
• 5 Effective stream restoration efforts in this region will require the alteration of local land-use activities that influence the physical habitat. Further development of empirical relationships between catchment activities and substrate and channel characteristics within natural geomorphic regions is essential for the evaluation of restoration projects.

     

Seasonal variation in vertical and horizontal movement of the freshwater bivalve Elliptio complanata (Mollusca: Unionidae)

1. Vertical and horizontal movement were studied in the freshwater bivalve Elliptio complanata at a sandy site in an oligotrophic lake over 3 years. Mussel movement did not vary significantly between day and night. On average, between 2 and 8% of 527 mussels moved each month during the ice-free season and the distance travelled by moving mussels averaged 0.6 cm day^–1.
2. Mussels were endobenthic during the winter, emerged from the sandy substrate in mid-May, peaked in sediment surface abundance in July, and descended into the sediments for the winter in September–October. Vertical displacement of mussels was closely correlated with water temperature although daylength may play a role. Mussels apparently move very little beneath the sediment during the winter.
3. The number of mussels moving horizontally at any given time was linearly correlated with daylength, but the distance travelled during a sampling period was related to daylength in a non-linear fashion. Greatest horizontal displacement of epibenthic mussels was found during spring and early summer, coincident with spawning in E. complanata     

Ionic Permeability of Insect Epithelia

In general, ionic regulation will depend on active transportby epithelia and also on the permeability properties of thesetissues. Passive permeability has recently been studied in thehindgut of the desert locust Schistocerca gregaria using electrophysiologicaland radiotracer techniques. Although locust rectum has low electricalresistance, cell membranes provide the major route for transepithelialionic diffusion; i.e., the locust rectum is a tight epithelium.Potassium permeability (P_K) is apparently regulated by luminalK and osmotic concentrations (local control), and also by thepeptide hormone CTSH (chloride transport-stimulating hormone).Transepithelial resistance declines when isolated recta areexposed to CTSH or its "second-messenger" cAMP (adenosine 3':5'-cyclicmonophosphate). Cyclic-AMP also stimulates K diffusion acrossrecta by 400%. Intracellular cable analysis indicatesthat cAMPlowers apical and basal membrane resistances (R_a and R_b, respectively)by {small tilde}80%; however different ionic permeabilitiesare affected at thelumen- and hemolymph-facing membranes: ThecAMP-induced decline in R_a, requires potassium whereas R_b isCl-dependent. The actions of cAMP on active transport and passivepermeability are complementary and would allow remarkably efficientcontrol over KC1 absorption in vivo. One hypothesis is as follows:CTSH elevates intracellular cAMP concentration by stimulatingadenyl cyclase. Cyclic-AMP enhances transepithelial Cl absorptionby stimulating a Cl pump in the apical membrane and also byincreasing the Cl permeability of the basal membrane. PassiveK absorption would also increase during cAMP stimulation sinceCl transport results in a more positive luminal potential, andbecause cAMP elevates transrectal P_K. The mechanisms by whichmembrane permeability is regulated in insects have not yet beenstudied, but these might involve the modulation of ion channelsby cAMP- or calmodulin-dependent phosphorylation, Ca or calmodulinbinding, methylation, or insertion of new channels into themembrane.     

Symbols of Substance: Bimin-Kuskusmin Models of Procreation,Death, and Personhood

The Bimin-Kuskusmin of the West Sepik interior of Papua New Guinea elaborate a complex folk theory of procreation that becomes the ‘natural’ foundation of some ideologically significant constructions of the individual, the person, gender, and societal continuity. Drawing on certain aspects of Weiner's model of reproduction and regeneration, symbols of substance and insubstantial ‘spirit’ that form this ‘natural’ foundation of the Bimin-Kuskusmin ideology of birth, death, and rebirth are explored in contexts of rites of passage that mark the course of the life-cycle from conception to death and ancestorhood. The key symbols of this cultural ideology are the enduring substances of bone, bone marrow, and finiik spirit, which are the basis of reckoning the cyclical regeneration of clan categories.