The Effect of Acid Feeding on Amine Formation in Barley

It is probable that one of the functions of potassium in theplant is to maintain the ionic balance of the cell, and it hasbeen suggested that in potassium deficiency, the productionof organic bases such as putrescine serves to balance an excessof organic acids which might occur under these conditions. Themechanism for the increase in activity of the enzymes in thepathway leading to the formation of putrescine in potassium-deficientbarley leaves was studied, therefore, by investigating the effectof artificially increasing the acidity by feeding inorganicacids to the roots of barley seedlings. Feeding hydrochloric acid caused significant increases in L-argininecarboxy-lase (arginine decarboxylase) and N-carbamylputrescineamidohydrolase activity in the leaves when expressed on thebasis of fresh weight, dry weight, total nitrogen, or proteinnitrogen, and a similar increase was induced on feeding sulphuricacid. Acid feeding did not cause a significant change in potassiumcontent on a dry-weight basis. The arginine, agmatine, and putrescinecontents were increased in the acid-fed leaves. The possibilitythat the increased arginine content in the acid-fed leaves ledto an increase in arginine decarboxylase by enzyme inductionwas investigated by feeding arginine through the roots to barleyseedlings. No increase in decarboxylase activity could be detected.     

The male genital tract and aedeagal components of the Diptera with a discussion of their phylogenetic significance

The male genital tract of Diptera is surveyed, based on whole dissections, with emphasis on nematocerous infraorders and especially the Culicomorpha. The genital tracts of all available nematocerous families are described and illustrated, including, for the first time, those of the families Thaumaleidae, Dixidae, Hesperinidae, and Pachyneuridae, and, as an outgroup, the mecopteran family Nannochoristidae (Mecoptera). On the basis of outgroup comparison, the Diptera + Mecoptera + Siphonaptera share the synapomorphies of accessory gland continuous with the vas deferens and U-shaped vasa deferentia. Further synapomorphies of the male genital tract provide evidence of the monophyly of the Mecoptera + Siphonaptera, Boreidae + Siphonaptera, and the Blephariceridae + Psychodidae + Trichoceridae + Anisopodidae + Brachycera. The Bibionomorpha, Culicomorpha, and Ptychopteromorpha share the synapomorphy of paired, two- to three-chambered accessory gland complexes, with secondary losses in Corethrellidae + Culicidae. It is concluded that there is no convincing evidence for the monophyly of the Chironomoidea. A sperm pump with an ejaculatory apodeme and the absence of a spermatophore are considered to be part of the ground plan of Diptera, but, because of uncertainty as to the identity of the basal lineage within Diptera and the homology of the sperm pump outside of Diptera, the polarity of these features cannot be presently interpreted.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 711–742.     

ADDITIONS AND SUPPLEMENTS TO THE MADAGASCAR AVIFAUNA

Langrand, O. & SINCLAIR, J.C. 1994. Additions and supplements to the Madagascar avifauna. Ostrich 65:302-310.

In order to update the data base on Madagascar birds, the literature is reviewed and museum records and unpublished data are taken into consideration. Records of unusual birds or species recorded for the first time in Madagascar are enumerated. For each new species the information associated with each record is presented, and an opinion is given if the record is acceptable or not. Twenty-two new species are proposed as additions to the list of Madagascar birds.     

The effect of selection for desiccation resistance on cold tolerance of Drosophila melanogaster

Abstract.  Low temperature and desiccation stress are thought to be mechanistically similar in insects, and several studies indicate that there is a degree of cross-tolerance between them, such that increased cold tolerance results in greater desiccation tolerance and vice versa . This assertion is tested at an evolutionary scale by examining basal cold tolerance, rapid cold-hardening (RCH) and chill coma recovery in replicate populations of Drosophila melanogaster selected for desiccation resistance (with controls for both selection and concomitant starvation) for over 50 generations. All of the populations display a RCH response, and there is no effect of selection regime on RCH or basal cold tolerance, although there are differences in basal cold tolerance between sampling dates, apparently related to inter-individual variation in development time. Flies selected for desiccation tolerance recover from chill coma slightly, but significantly, faster than control and starvation-control flies. These findings provide little support for cross-tolerance between survival of near-lethal cold and desiccation stress in D. melanogaster .     

Drought-induced leaf shedding in walnut: evidence for vulnerability segmentation

Trees of Juglans regia L. shed leaves when subjected to drought. Before shedding (when leaves are yellow), the petioles have lost 87% of their maximum hydraulic conductivity, but stems have lost only 14% of their conductivity. This is caused by the higher vulnerability of petioles than stems to water-stress induced cavitation. These data are discussed in the context of the plant segmentation hypothesis.     

Carbon Dioxide and Water Vapour Exchange of Leaves on Field-Grown Citrus Trees

Carbon dioxide and water vapour exchange rates were measuredon attached leaves of field-grown citrus trees. The exchangerates were measured continuously during several weeks in thespring of two successive years. These data confirmed the ratherlow rates of maximum CO₂ exchange (6–11 µmol m^–2s^–1) by citrus leaves. However, the maximum rate was maintainedthrough the midday period on only about half the days. On theother days, characterized by high temperatures and high atmosphericwater vapour pressure deficits, pronounced midday depressionsin CO₂ exchange rates were observed. Since midday transpirationremained stable at a constant rate even with increasing vapourpressure deficit, these results indicate that stomatal closurewas occurring. In fact, the data suggest tfiat specific, maximumtranspiration rates were associated with differing rootstocks.Thus, the rate of water supply to the leaves may be an importantfactor in determining the maximum transpiration rate, and therebymediating control of stomatal conductance and the resultantmidday depression in CO² exchange rates.     

The natural regulation of buffalo populations in East Africa: The food supply as a regulating factor,and competition*

Evidence is presented to show that both the quality and quantity of food available to a buffalo population falls below the minimum maintenance requirements of that population at certain times of the year. In the Serengeti grasslands there was a shortage of the only good quality component, grass leaf, in the dry season, with the result that the animals consumed an increasing proportion of poor quality food such as grass stem. By the end of the dry season the diet had dropped in quality below the minimum maintenance level. In areas such as Mt. Meru where there was a more continuous growing season, the high density of animals kept the standing crop of leaf at a low level. During the cooler dry season the growth of leaf became insufficient in quantity for the maintenance requirements of the population. These two quite different situations suggested that food shortage was a more general phenomenon in eastern Africa. Various measurements of feeding behaviour were made. Total grazing time per 24 h did not differ between seasons but ruminating time may have increased as the season became drier and could have been a response to the more fibrous food. Analysis for cycles of activity showed that there was more temporal organization during the dry season. These changes in activity cycles appeared to be related to the increase in energy expenditure produced by heat stress and sweating. Old animals with poor teeth did not compensate for the poor food supply by changing their feeding behaviour. There was a positive relationship between annual rainfall and mean crude density in different areas of eastern Africa, indicating that regulation was taking place. Since rainfall determined the amount of available food, it could have operated through the food supply. On a finer scale it was found that the extent of the preferred riverine habitats was also related to density. Thus rainfall, the extent of riverine habitat and perhaps soil moisture were three limiting factors that determined mean density and all could have taken effect through the food supply. As a result of initial selective grazing the amount of available leaf declined as the dry season progressed to the extent that by the end of the season the proportion of this component in the diet fell to a very low level. The impact of the population on its limited food supply indicated that intra-specific competition was acting as the cause of regulation. Measurements of wildebeest eating the same food in the same habitats as buffalo showed that inter-specific competition was also taking place. A small proportion (7“) of the wildebeest population could have reduced the buffalo population by approximately 18^o,‘, from its potential population size. The buffalo population in the Serengeti was regulated by adult mortality which was caused by undernutrition as a result of food shortage. This food shortage was caused by intra- and inter-specific competition. The effect of predation and disease was to hasten the response of the population to changes in the food supply. The limiting factors determining the mean level of the available food were, amongst others, rainfall, soil moisture and the extent of the preferred riverine habitat. The effect of interspecific competition could result in a complex regulation of populations through their food supply. There appears to be no foundation for hypotheses which invoke over-utilization or damage as a consequence of regulation through food.     

Composition and Behavior of the Nucleolar Organizer of the Nucleolar Variant of Axolotls; Review and Comparison to Other Systems

SYNOPSIS. Studies on the nudeohis in various species of Amphibia,including the Mexican axolotl, have contributed to an understandingof the function of the nucleolar organizing region. In the firstpart of this paper we have reviewed some of the research onnucleolar variants in the axolotl. These variants were recognizedin different strains of laboratory reared animals. The phenotypesinclude diminished nucleolar size and possible alterations inthe levels of rDNA. The expression of several of these variantnucleolar phenotypes does not, however, reflect a simple deletionof rRNA genes. Evidence from analyses of several mutant andapparently normal strains indicate that some animals have relativelyhigh levels of rRNA redundancy, while others, including someanimals which display variant nucleolar sizes, display "normal"levels. Data on the inheritance of rRNA genome sizes in the axolotlis reviewed. The observation that intermediate levels of redundancywere detected in some crosses is discussed in terms of inheritancedata from other organisms. In the second part of this reviewa variety of information, obtained from studies of various organisms,on nucleolar expression is discussed.