Sealed lysimeters for the direct estimation of dinitrogen fixation by grain legume crops

Abstract A new technique has been devised for the direct estimation of the contribution of N₂-fixation to the total nitrogen of a legume crop. Sealed lysimeters and ancillary equipment are described by which it is possible to enclose in a gas-tight system the roots of some of the plants within the crop, together with their associated core of soil. The normal soil atmosphere can then be replaced by one containing ¹⁵N₂, thus allowing, from the ¹⁵N content of the resulting plants direct calculation of the N₂-fixation. Regular monitoring is necessary to ensure that soil O₂, CO₂ and moisture contents are maintained at normal field levels. The results indicate that the technique is capable of achieving its objectives and, provided the seedlings establish well initially, the resultant plants fully match the field average at final harvest. It has been possible to maintain the labelling of the soil atmosphere sufficiently constant to ensure that reliable and highly reproducible estimates of N₂-fixation are obtained. Using Pisum sativum cv. Meteor at densities of 160 plants m^?2, fixation accounted for about 90% of the total nitrogen uptake. The limitations and merits of the method are compared with those of the ¹⁵N-fertilizer dilution method.     

DEFENDING THE DUTY TO RESEARCH?

In 2005, John Harris published a paper in the Journal of Medical Ethics in which he claimed that there was a duty to support scientific research. With Sarah Chan, he defended his claims against criticisms in this journal in 2008. In this paper I examine the defence, and claim that it is not powerful. Although he has established a slightly stronger position, it is not clear that the defence is sufficiently strong to show that there is a duty to support scientific research. Important questions about fairness, about rescue, and about the relationship between reasons and obligations to act can still be raised; and these questions are important enough to destabilize the defence.     

A simple route to maximum-likelihood estimates of two-locus recombination fractions under inequality restrictions

Journal of Genetics -     

Stimulation of Delayed Light Emission by Salt Gradients and Estimation of the Relative Ionic Permeabilities of the Thylakoid Membranes

The sudden addition of various salts to pre-illuminated ohloroplastsenhances the rate of delayed light-emission. It is argued thatthis stimulation of luminescence is, with some salts, due entirelyto the electrical potential developed as the ions diffuse acrossthe thylakoid membranes. By varying the magnitude of the concentrationgradients and applying the Goldman voltage equation it has beenpossible to obtain quantitative estimates for the relative ionicpermeabilities of the thylakoids. It seems that chloride permeatesas much as 10 times slower than K⁺. Predictions of the effectsof using mixed salt solutions and of preincubation of the chloroplastswith salt at various levels have been made and tested experimentally.From this it is apparent that the action of salts of weak acids,such as benzoic acid, although particularly effective in stimulatingluminescence, cannot be satisfactorily explained on the diffusionpotential hypothesis. Over all the results seem to give quantitative information onthe relative ionic permeabilities of the thylakoids and supportsthe model that delayed light may originate from a charge transfercomplex specifically orientated in this membrane system.     

Senescence-Dependent Increase in the Permeability of Liposomes Prepared from Bean Cotyledon Membranes

Liposomes containing 79 mM Tris-acetate and 50 mM KCl were preparedfrom the total lipid extracts of smooth microsomal membranesisolated from 2, 4, 7 and 9 d old bean cotyledons. Permeabilityto glycerol was determined by spectrophotometric measurementsof osmotic swelling when the liposomes were placed in eitherisotonic or slightly hypotonic glycerol. For liposomes from2 and 4 d old membrane there was a time-dependent decrease inabsorbance at 450 nm from which initial swelling rates reflectingthe influx of glycerol and water were calculated. At 25 °Cthese rates were not significantly different For liposomes from7 and 9 d old membrane there was no change in absorbance withtime at 450 nm signifying that these older liposomes were equallypermeable and non-electrolytes and non-electrolytes, and thereforeincapable of swelling. Permeability to glucose was determinedby preparing the liposomes in a solution of the sugar, passingthem through a Sephadex column to eliminate unsequestered glucose,and quantifying sugar leaked from the liposomes over time bymeasuring NADPH formation through the tandem actions of hexokinaseand glucose-6-phosphate dehydrogenase. The rate constants forglucose leakage from 2 and 7 d old liposomes were 0.55 and 3.94respectively, again indicating a dramatic increase in permeabilitywith advancing age. These changes in permeability correlatetemporally with the appearance of gel phase lipid in both liposomesand the membranes from which they were derived, suggesting thatthe coexistence of discrete liquid-crystalline and gel phaselipid domains renders membranes leaky and contributes to lossof intracellular compartmentation in senescing tissue.     

Bigger? Fatter? Or is faster growth better? Considerations on condition in larval and juvenile coral-reef fish

Abstract Analyses of condition data are conspicuous by their paucity in the extensive tropical reef-fish literature. Researchers typically quantify abundance at settlement, with little regard for the demonstrably variable quality of newly settled fishes. Condition may be functionally classified by indices of growth (e.g. the RNA-DNA index or peripheral growth increments of the otolith), starvation (e.g. height of midgut mucosal cells), storage (e.g. lipid content), or morphometry (e.g. dry weight/length’), all of which are variably correlated with each other. At present all indices are species-, stage-, technique- and therefore often investigation-specific, as laboratory-reared larvae for calibrating field-collected condition indices are often specific to the rearing procedure. RNA indices are particularly appropriate for estimating larval condition. In pelagic juveniles, or in recently settled juveniles, the width of peripheral growth increments of the otolith estimates average growth rate in length or dry weight during the previous few days, which discerns increasing from decreasing condition. Increment width changes in otoliths are particularly responsive to starvation events, and are correlated with RNA indices. Growth indices have great potential for determining which individuals were growing faster, thereby reducing their pelagic duration, and thus increasing their survival potential. The recent debate regarding whether bigger larvae have better survival could be re-addressed, by determining if larvae with faster growth indices have relatively enhanced survival.