The Membrane-Bound Forms of the Mitochondrial ATPase of Turnip (Brassica napus L.) and Mung Bean (Phaseolus aureus): Characterization and Investigation of Factors Controlling Activity

Isolated intact plant mitochondria, including those from turnipand mung bean, show low endogenous Mg²⁺-ATPase activity and,unlike mammalian mitochondria, lack significant uncoupler-stimulatedATPase activity. In contrast, the rates of respiration-drivenATP synthesis are comparable to those in mammalian mitochondria,suggesting the presence of an ATPase inhibitor. Disruption ofintact turnip mitochondria only results in limited increasesin ATPase activity, indicating that a permeability barrier toATP transport is not primarily responsible for the low endogenousactivity. The ATPase activity of turnip mitochondria and membraneparticles can be increased up to 50-fold when assayed underoptimum conditions. Time-dependent increases in activity inducedby ageing, exposure to salts and trypsin treatment, are allconsistent with an inhibitor protein being responsible for thelow endogenous activity and lack of uncoupler-stimulation. TheATPase activity of particles under optimum conditions and afterageing is sufficient to account for the rates of ATP synthesis.After activation, turnip mitochondrial ATPase activity is similarto the mammalian enzyme in inhibitor sensitivity, pH optimum,bivalent cation requirement, and sensitivity to ‘activatinganions’. In mung bean mitochondria, a permeability barrierto ATP is only partly responsible for the low endogenous ATPaseactivity, together with the inhibitory factor. On the basisof variation in the relative Ca²⁺ and Mg²⁺ -ATPase activitiesafter various treatments, a Ca²⁺-regulatory site which affectsATPase activity is proposed to exist in the F₁ATPase complex. Key words: Plant mitochondrial ATPase, calcium/magnesium -ATPase, inhibitor+ nucleotide specificity, cation/anion effects     

Potential novel hosts for the lily leaf beetle Lilioceris lilii Scopoli (Coleoptera: Chrysomelidae) in eastern North America

Abstract.  1. Introduced insects often incorporate native plants into their diets and might be expected to show a predilection for novel hosts that are phylogenetically related to their normal hosts. The lily leaf beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), is an introduced pest of cultivated lilies. Oviposition behaviour, larval behaviour, and development of L. lilii was examined on a range of potential host plants, as well as on the normal host, Asiatic hybrid lilies Lilium sp.
2. Neonate larval feeding behaviour was quantified on 15 food plant species: 10 from the Liliales, three from the Asparagales and two eudicots. Larvae fed plants closely related to the genus Lilium were more likely to initiate feeding, less likely to abandon their food leaf, and consumed more leaf area.
3. In no-choice tests, females oviposited on the novel hosts Lilium philadelphicum , Medeola virginiana , Clintonia borealis , Streptopus amplexifolius , and Polygonatum biflorum ; however, all but L. philadelphicum received very few eggs. Non- Lilium novel hosts were not used for oviposition when presented along with Asiatic lilies in choice tests.
4. A single individual was reared to the adult stage on the novel host S. amplexifolius . Several larvae survived to the pupal stage on M. virginiana , although no adults emerged from those pupae. Larvae reared on the native wood lily L. philadelphicum performed equally well or better than on the Asiatic cultivar.
5. Our results indicate that the lily leaf beetle poses a threat to native Liliaceae. Several native Lilium species, including L. philadelphicum , are threatened or endangered in certain jurisdictions throughout their range; these species should be monitored closely for colonisation by the beetle.     

Age-specific Chaoborus predation on rotifer prey

SUMMARY. 1. This is the first study to examine predator-prey interactions between Chaoborm instars and rotifer prey. The predatory behaviour of instars I–III of Chaoborus pimctipennis and the diet selectivity of instars I—IV feeding on rotifers were examined in the laboratory. Prey used in direct observations of predatory behaviour included a variety of rotifers (Symhacta pectlnata, S. ohUmga, Polyarthra remata, Asplanchna girodi, Keratella crassa, spined and unspined forms of Keratella cochlearis) and two crustaceans (Bosmitia longirostris, Mesocyclops edax nauplii. 2. In general, strike efficiencies (percentage of strikes resulting in inges- tion) increased in successive instars I—III. Early instar (I and II) strike efficiencies were low when compared with other invertebrate predators. For a given instar. mean prey handling times varied among prey species more than strike efficiencies. Mean handling times for small, soft-bodied rotifers were lowest and those for wide, hard-bodied prey were highest. 3. Instar I exhibited significantly greater selectivity for the small, soft- bodied S. obUmga than for the larger S. pectinata, hard-bodied K. crassa, and spined and unspined forms of K. cochlearis. Instars II—IV positively selected both the large and small Symhaeta species over all Keratella species. The relationship between Chaobortts selectivity and prey value (weight of prey per unit handling time) can be described by a power function. Ingestion rates of rotifers by older instars (III and IV) are among the highest reported for invertebrate predators. 4. Rotifer vulnerability to Chaoborus predation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected from Chaoborus predation because Chaohorus can manipulate and swallow them. Giguere et al.'s 1982) encounter rate model must be modified to predict encounter rates of slow-moving rotifer prey with Chaohorus.     

Time-course of inorganic nitrogen uptake and incorporation by natural populations of freshwater phytoplankton

SUMMARY. 1. Time-course measurements of NH₄⁺ and NO₃⁻uptake were made on the natural phytoplankton populations in a eutrophic lake at a time when these nutrients were at their lowest annual concentration.
2. Both NH₄⁺ and NO₃⁻ uptake was increased at least five-fold during the first 5 min of incubation following near saturating pulses of these nutrients.
3. Elevated uptake was also observed following low level (∼2μg N 1⁻¹) pulses of NH₄⁺ and NO₃⁻, but substrate depletion during the first hour of incubation may have been partially responsible for this apparent enhancement.
4. Incorporation of ^I5N into TCA-insoluble material (protein) following the saturating NH₄⁺ pulse was increased less than total cellular ¹⁵N uptake, whereas no elevation of ¹⁵N incorporation into protein was observed following a saturating NO₃⁻pulse.
5. The percentage of ^I5N incorporated into protein, with respect to total cellular uptake, was ∼32% and ∼12% for NH₄⁺ and NO₃⁻, respectively, following 5 h of incubation.     

Factors affecting the microdistribution of Gammarus pulex (Amphipoda): an experimental study

SUMMARY. 1. The tnierodistribution of Gammarus species is size assortative: larger animals are associated with larger substrate particles. Using an artificial stream with scrubbed substrate we investigate the hypothesis that the assortative mechanism is stimulated by current avoidance rather than food searching.
2. In uniformly mixed substrate, G. pulex tend to move upstream, but in patchy substrate they are found in a predictable substrate grade. There is no discrimination between patches by different size classes of G. pulex in static water. The size assortative field pattern can only be reproduced under flow conditions in the laboratory. It occurs in the absence of food and irrespective of the sequence or location of substrate patches.
3. As density increases, G. pulex are displaced from the optimal patches but move into the open stream rather than into the cover of alternative patch types.
4. We discuss the significance of these results and suggest that some earlier models explaining mechanisms for microdistribution patterns tnay have been unnecessarily complex. Contrasts between natural and simulated stream situations and their experimental advantages are noted.     

Mating system and nesting biology of the Red-necked Phalarope Phalaropus lobatus: what constrains polyandry?

In this five-year study of Red-necked Phalaropes on the coast of Hudson Bay, Canada, only 8% (5/59) of females were polyandrous. Seventy-five percent were monogamous, and 17% did not obtain mates. All males obtained mates readily. To understand the low incidence of polyandry in this sex-role reversed, non-territorial mating system, aspects of the pair bond, nesting biology, and size and plumage dimorphism were examined.
Pair bonds lasted an average of 11 days and ended as soon as the clutch was completed. Polyandrous females initiated their second nests only seven days later. Since in most years nest initiation for the population as a whole spanned three weeks, there was ample time for multiple clutches. Energetic constraints may have played a limited role in constraining polyandry, but many females that had previously laid clutches courted incubating males or harassed pairs.
The major factor limiting polyandry appeared to be availability of mates. Because phalaropes generally breed in habitats that are less defensible than those of other role-reversed shorebirds, they are less able to monopolize males in populations with equal sex ratios. Sexual size dimorphism is correspondingly smaller than in territorial role-reversed shorebirds, although plumage variation between and within sexes in this study was strong (and invariant with age). Thus, despite the phalaropes' role-reversal, the evidence indicates that monogamy may predominate, with sexual selection driven by the ability of females to produce second clutches opportunistically when receptive males are available.     

The influence of pair-status on the breeding behaviour of the Kittiwake Rissa tridactyla before egg-laying

The breeding behaviour of individually marked Kittiwakes Rissa tridactyla that retained mates from the previous year (SAME) was compared, over the period from pair-formation to egg-laying, with those that changed mates (CHANGE). Position of nest-site in colony and breeding experience did not differ in the two groups studied. Hirds in CHANGE pairs attended the nest-site more frequently and as a result probably had less 'off-duty' time during which to forage. Rates of greeting were higher in CHANGE pairs. Differences between the two groups were usually greatest during the first two weeks after pair-formation an decreased toward egg-laying. CHANGE pairs copulated over a longer period before egg- laying, but stopped copulating sooner than SAME pairs. Copulation rates were higher in SAME pairs immediately before egg-laying. The causation of the behavioural differences between the two groups is discussed in terms of mate familiarity. It is suggested that the recorded differences explain the lower reproductive success in CHANGE pairs reported by other workers.     

Relationships between Acetylene Reduction Activity, Hydrogen Evolution and Nitrogen Fixation in Nodules of Acacia spp.: Experimental Background to Assaying Fixation by Acetylene Reduction under Field Conditions

Hansen, A. P., Pate, J. S. and Atkins, C. A. 1987. Relationshipsbetween acetylene reduction activity, hydrogen evolution andnitrogen fixation in nodules of Acacia spp.: Experimental backgroundto assaying fixation by acetylene reduction under field conditions.—J.exp. Bot. 38: 1–12 Glasshouse grown, symbiotically-dependent seedlings of Acaciaalata R.Br., .A. extensa Lindl., and A. pulchella R.Br. wereexamined for acetylene reduction in closed assay systems usingundisturbed potted plants, excavated whole plants, nodulatedroots or detached nodules. Nitrogenase activity declined sharplyover the first hour after exposure of detached nodules to acetylene(10% v/v in air), less steeply or not at all over a 3 h periodin assays involving attached nodules. Using detached nodules,rates of acetylene reduction, nitrogen (¹⁵N₂) fixation, andhydrogen evolution in air (¹⁵N₂) and acetylene-containing atmosphereswere measured in comparable 30 min assays. Total electron flowthrough nitrogenase in air was determined from rates of nitrogen(¹⁵N₂) fixation ( ? 3) plus hydrogen evolution, that in thepresence of acetylene from rates of acetylene reduction andhydrogen evolution in air: acetylene. Values for the ratio ofelectron flow in air: acetylene to that in air ranged from 0?43to 0?83 in A. pulcheila, from 0?44 to 0?66 in A. alala and from0?37 to 0?70 in A. extensa, indicating substantial inhibitionof electron flow through nitrogenase of detached nodules byacetylene. Relative efficiencies of nitrogenase functioningbased on hydrogen evolution and acetylene reduction were from0?15 to 0?79, those based on nitrogen (¹⁵N₂) fixation and hydrogenevolution from 0?53 to 0?87. Molar ratios of acetylene reducedto nitrogen (¹⁵N₂) fixed were 2?82 ? 0?24, 201 ? 0?15, and 1?91? 0?11 (?s.e.; n = 7) for A. pulcheila,A. extensa and A. alata respectively A standard 5–10 min acetylene reduction assay, conductedon freshly detached unwashed nodules in daytime (12.00–14.00h), was calibrated for field use by comparing total N accumulationof seedlings with estimated cumulative acetylene reduction overa 7-week period of glasshouse culture. Molar ratios for acetylenereduced: nitrogen fixed using this arbitrary method were 3?58for A. alata, 4?82 for A. extensa and 1?60 for A. pulchella.The significance of the data is discussed. Key words: Acacia spp, nitrogenase functioning