Oxygen Diffusion in Lupin Nodules: II. MECHANISMS OF DIFFUSION BARRIER OPERATION

The oxygen diffusion resistance of Lupinus albus (L.) cv. Multoluparoot nodules was increased by subjection to short-term stresses;lowering rhizosphere temperature from 25 to 16 °C (2 h),detopping plants (3 h), darkening plants (21 h) or exposingroots to 20 mol m^–3 KN03 for 2, 4 or 6 d. Microscopicobservations and measurements showed that this resulted in thearea of open intercellular spaces within the inner cortex beingreduced due to both cell expansion and increased productionof an occluding glycoprotein. Electrophoretic and Western Blotanalysis using the monoclonal antibodies MAC236 and MAC265 showedtwo distinct glycoprotein antigens with molecular weights of240 and 135 kDa, respectively. Both antigens are localized withinintercellular spaces of the inner cortex. The amount of glycoproteinwas determined using either ELISA, with MAC265, or quantificationof immunolabelling with MAC236. This immunolabelling also localizedthe glycoprotein within globules adhering to the inside of theinner cortical cell walls. Key words: Oxygen diffusion resistance, glycoprotein, nodules, nitrogen fixation, Lupinus albus     

Hypoxic Reptiles: Blood Gases, Body Temperature and Control of Breathing

Our contribution to this symposium is a review of recent modelsand experimental cdata on oxygen homeostasis in vertebrateswith normal intracardiac shunts; i.e., amphibians and reptiles.We focus on the interactions among hemoglobin function, bodytemperature regulation, and cardiovascular shunts under normalconditions (i.e., breathing fresh air at or near sea level)and during external hypoxia (e.g., altitude, burrows) and internalhypoxia (e.g., anemia, hemorrhage). Mathematical models andexperimental data suggest that animals with venous admixturefrom cardiovascular shunts will show biphasic arterial and mixedvenous Po₂ responses to warming; i.e., first increasing andthen, as the dissociation curve shifts too far to the right,decreasing. This has implications for many physiological functionsincluding oxygen consumption by tissues, control of breathing,as well as preferred body temperature and its regulation. Wepresent some of the recent experiments that have explored theseimplications.     

Oxygen Diffusion in Lupin Nodules: I.VISUALIZATION OF DIFFUSION BARRIER OPERATION

Root nodules of Lupinus albus (L.) cv. Multolupa were subjectedto short- and medium-term stresses by lowering rhizosphere temperaturefrom 25 to 16°C (2 h), detopping plants (3 h), darkeningplants (21 h) or exposing roots to 20 mol m^–3 KNO₃ for4 d. All experimental treatments produced increases in oxygendiffusion resistance, compared with control plants. These correlatedwith structural changes in the nodule cortex, which is describedin detail for the first time. The most noticeable change isthe occlusion of intercellular spaces by a glycoprotein whichwas identified using the monoclonal antibody MAC236. This glycoproteinwas also found surrounding bacteria in intercellular spacesof the cortex of control nodules. Key words: Oxygen diffusion resistance, glycoprotein, nodules, nitrogen fixation, Lupinus albus     

Measurement and mapping of avian diversity in southern Africa: implications for conservation planning

The potential and problems of using species diversity information, derived from the Southern African Bird Atlas Project (SABAP), are examined. Atlas data were analysed and the problem of uneven sampling effort was ameliorated through an application of an index of diversity. Maps of diversity for various suites of species are considered in relation to their implications for conservation planning. An approach to the identification of high-priority areas for conservation, based on an index of diversity, is described and called the Compatible Sets Approach. Birds in the grassland biome are used to illustrate the principles of the approach.     

Bioenergetics, Exercise, and Fatty Acids of Fish

The bioenergetic aspects of pentachlorophenol poisoning andexercise in fish are discussed. When cichlids are exposed to0.2 ppm of pentachlorophenol, the intake of food was increasedand energy losses were also increased. Growth was decreased.The cost of specific dynamic action was higher and the costof exercise was increased above the cost of similar exercisein nonpoisoned controls. In salmon swimming to exhaustion at52 cm/sec fatty acids 18:1, 16:0, and 16:1, and at 59 cm/secfatty acids 22:6, 18:2, and 20:4 suffered the greatest depletion.At 52 and 59 cm/sec, respectively, average exhaustion timeswere 1141 and 398 minutes; the equivalents of distance traveledwere 26.0 and 12.7 miles; the loss in lipids, 54 and 10 mg;and the average weight losses, 830 and 480 mg per salmon. Totalcaloric losses calculated from the data on lipid and weightlosses were approximately 1118 and 566 calories. Calculatedfrom the data of Brett (1964) on O₂ consumption, caloric losseswere estimated at only 344 and 188 calories. The differencebetween observed values and values calculated from the dataof Brett may lie in the duration and severity of the exercise.Brett collected his data on O₂ consumption on the basis of atmost two hours at high velocity. Possibly when maximum effortis involved each succeeding mile and each succeeding hour ismore difficult and more costly to the salmon.     

Structural Equation Modeling for Observational Studies

Abstract Structural equation modeling (SEM) represents a framework for developing and evaluating complex hypotheses about systems. This method of data analysis differs from conventional univariate and multivariate approaches familiar to most biologists in several ways. First, SEMs are multiequational and capable of representing a wide array of complex hypotheses about how system components interrelate. Second, models are typically developed based on theoretical knowledge and designed to represent competing hypotheses about the processes responsible for data structure. Third, SEM is conceptually based on the analysis of covariance relations. Most commonly, solutions are obtained using maximum-likelihood solution procedures, although a variety of solution procedures are used, including Bayesian estimation. Numerous extensions give SEM a very high degree of flexibility in dealing with nonnormal data, categorical responses, latent variables, hierarchical structure, multigroup comparisons, nonlinearities, and other complicating factors. Structural equation modeling allows researchers to address a variety of questions about systems, such as how different processes work in concert, how the influences of perturbations cascade through systems, and about the relative importance of different influences. I present 2 example applications of SEM, one involving interactions among lynx (Lynx pardinus), mongooses (Herpestes ichneumon), and rabbits (Oryctolagus cuniculus), and the second involving anuran species richness. Many wildlife ecologists may find SEM useful for understanding how populations function within their environments. Along with the capability of the methodology comes a need for care in the proper application of SEM.