Cell-Cell Interactions and Distal Outgrowth in Amphibian Limbs

SYNOPSIS. A current model concerning the process of limb regenerationin vertebrates is examined. According to this model (Bryantet al, 1981), new positional values in the proximal-distal limbaxis are laid down as a result of local interactions betweencells in the limb circumference. Cells with disparate circumferentialpositional values come together at the site of future outgrowthand intercalation between them generates more distal levelsof the pattern. The results of a number of experiments on surgicallycreated symmetrical limb stumps are discussed in relation tothis model. In addition, an extension of this model to accountfor digit formation is presented, and the implications of thisformulation for limb evolution are discussed.     

Post-juvenile dispersal of Hazel Grouse Bonasa bonasia in an expanding population of the southeastern French Alps

We studied the post-juvenile dispersal of 18 radiotagged juvenile Hazel Grouse Bonasa bonasia (14 males, four females) in an expanding population in the southeastern French Alps between 1998 and 2001. The mean dispersal distances between the capture sites of juveniles in September–October and the centre of the home range in the following spring was 4 km for males (range 0.1–24.9 km) and 2 km for females (range 0.2–5.6 km). The distances recorded for two long-dispersing males (15 and 24.9 km) are greater than those reported to date for Hazel Grouse. Using our radiotracking data, we interpret the pattern of range expansion that has been occurring since the 1950s around our study area. Barriers to dispersal included rocky ground and other alpine habitats above 2000 m and over 1 km wide, but Hazel Grouse did cross open agricultural land at lower elevation. Two patterns of dispersal movements were recognized in juveniles: erratic movements that led to settlement on or near the natal site, and direct movements to a new range relatively far from the natal area. We discuss the adaptive consequences of these different behaviour patterns.     

Species number, species abundance and body length of arboreal arthropods associated with an Australian rainforest tree

Abstract.

• 1 The species number, the abundance per species and the body length of arthropods foraging within the crowns of an over-storey rainforest tree from Australia, Argyrodendron actinophyllum (Sterculiaceae), were investigated by interception trap sampling and restricted canopy fogging. Emphasis was placed upon the interpretation of trap data. Arthropods were trapped continuously day and night, over a 2-year period and the final analyses examined the attributes of 759 species which represented 20,500 individuals.
• 2 The proportion of‘rare’species (Le. collected once) intercepted was high (35.7%), although lower than in other similar rainforest surveys. Neither the α log-series nor the log-normal distribution could be fitted to the relationship between number of species and number of individuals, since the number of rare species was much higher than predicted and the mode of the distribution could not be identified. The proportion of rare species was higher in fogging collections (452%) than in trap collections.
• 3 The data are compared with a study of Bornean arboreal beetles, obtained by fogging trees during a single sampling event. Several patterns were common to both data sets. However, the three-dimensional plot of the variables describing the structure of the arthropod community showed a notably rougher surface than in the case of Bornean beetles.
• 4 Although several factors may complicate the interpretation of the three-dimensional plots, long-term and continuous sampling may alter our perception of complex arthropod communities. This methodology is imperative for a proper understanding of arthropod community structure in rain forests.

     

The Structure of Calf Liver Cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>5</Subscript> at 2.8 Å Resolution

CYTOCHROME b₅ is a haem-containing protein in the microsomes of liver tissue. It interacts specifically with a flavo-protein, cytochrome b₅ reductase, which catalyses the transfer of electrons from NADH to the haem iron of the cytochrome¹. The microsomal cytochrome b₅ system has been implicated in fatty acid desaturation reactions² and a similar system in erythrocytes may catalyse the reduction of methaemoglobin³. Calf liver cytochrome b₅, solubilized by pancreatic lipase, has a molecular weight of 11,000 and consists of ninety-three amino-acids in the sequence shown in Fig. 1 (refs. 4 and 5). The haem group is non-covalently bound to the protein and can be removed reversibly by acid acetone treatment⁶.     

Regulation of Stable RNA Synthesis in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Comparison of gene dosage and the rate of stable RNA synthesis suggests that cytoplasmic elements are involved in its regulation.     

Taxonomy of the Houbara Bustard Chlamydotis undulata subspecies considered on the basis of sexual display and genetic divergence

The Houbara Bustard Chlamydotis undulata is a polytypic species with three subspecies classified according size, colour and distribution: C. u. undulata, C. u. fuertaventurae and C. u. macqueenii. A comparative study of the male display behaviour of these three subspecies has shown similarities between C. u. undulata and C. u. fuertaventurae , whereas appreciable differences exist in the visual and auditory aspects of the display between C. u. undulata and C. u. macqueenii. These observations make the current taxonomy of Houbara Bustard questionable, particularly in view of the major importance of the sexual display in bird speciation processes. Furthermore, DNA analysis of the cytochrome b gene indicates the existence of a significant differentiation between the C. u. undulata and C. u. macqueenii populations. These findings indicate the need for a revision of the taxonomy of genus Chlamydotis which should separate the macqueenii and undulata populations at species rank. Until further investigations are completed, C. u. fuertaventurae should be kept as a subspecies of undulata since the courtship display is alike in both populations.     

Phloem Mobility of Boron is Species Dependent: Evidence for Phloem Mobility in Sorbitol-rich Species

Boron is generally considered to be phloem immobile or to haveonly limited phloem mobility in higher plants. Evidence suggests,however, that B may be mobile in some species within thePyrus,Malus andPrunusgenera. These genera utilize sorbitol as a primarytranslocated photosynthate and it has been clearly demonstratedthat B forms stable complexes with sorbitolin vitro.In the researchpresented here we demonstrate, further, that B is freely phloemmobile inPyrus, MalusandPrunusspecies and suggest that thisis mediated by the formation and transport of B-sorbitol complexes. The pattern of B distribution within shoot organs and the translocationof foliar-applied, isotopically-enriched¹⁰B was studied in sixtree species. Results demonstrate that in species in which sorbitolis a major sugar (sorbitol-rich), B is freely mobile while inspecies that produce little or no sorbitol (sorbitol-poor) Bis largely immobile. The sorbitol-rich species used here werealmond [Prunus amygdalusB. syn.P. dulcis(Mill.)], apple (MalusdomesticaB.) and nectarine (Prunus persicaL. B. var.nectarinaM.),sorbitol-poor species included fig (Ficus caricaL.), pistachio(Pistacia veraL.) and walnut (Juglans regiaL.). In sorbitol-richspecies foliar applied¹⁰B was transported from the treated leavesto adjacent fruit and specifically to the fruit tissues (hull,shell or kernel) that developed during the experimental period.Whereas, foliar-applied¹⁰B was rapidly translocated out of leaves,only a small percentage of the¹¹B present in the leaf at thetime of foliar application was retranslocated. In sorbitol-richspecies, B concentrations differed only slightly between oldand young leaves while fruit tissue had significantly greaterB concentrations than leaves. In contrast, sorbitol-poor specieshad significantly higher B concentrations in older leaves thanyoung leaves while fruit tissue had the lowest B concentration.This occurred irrespective the source of plant B (soil, solutionor foliar-applied). In a subsequent experiment the growth ofapple trees in solutions free of applied B was maintained solelyby foliar applications of B to mature leaves. These resultsindicate that B is mobile in species that produce significantamounts of sorbitol. We propose that the mobility of B in thesespecies is mediated by the formation of B-sorbitol complexes. Almond; Prunus amygdalus ; apple; Malus domestica; nectarine; Prunus persica; fig; Ficus carica; pistachio; Pistacia vera; walnut; Juglans regia; boron; phloem mobility; deficiency; toxicity; inductively coupled plasma-mass; spectrometer     

A Novel Experimental System for Studies of Photosynthate Transfer in the Developing Wheat Grain

The aim of this study was to develop a valid and convenientexperimental system for exploring photosynthate transfer inthe developing wheat grain. Structural characteristics relatingto photosynthate transfer and the composition of the endospermcavity sap were examined during the linear stage of grain developmentat 25±3 d after anthesis. Based on the results of thesestudies, an experimental system was devised to permit the directmonitoring and manipulation of photosynthate transfer from theendosperm cavity to the storage endosperm. A novel approachwas used whereby insertions were made into the endosperm cavityby a needle at the embryo end and a piece of microcapillarytubing at the stigma end of the detached grain. By this means,the experimental solution was delivered into and flowed longitudinallyunder gravity through the endosperm cavity to exit at the stigmaend. The composition of the experimental solution reflected the principalsolute concentrations and osmolality of the in vivo endospermcavity contents. With the introduction of the solution intothe cavity, it was found that the viability of grain tissueswas maintained for up to 30 h. During a 24 h period both therate of sucrose uptake and subsequent incorporation into ethanolinsolublecomponents were shown to reproduce the rate of starch biosynthesisand in vivo grain growth. Moreover, the experimental systemeffectively reproduced the in vivo pathway of photosynthatetransfer from the endosperm cavity via the modified aleuronecells into the endosperm. As a result, this system providesa new approach to study photosynthate transfer in the developingwheat grain. Key words: Wheat grain, endosperm cavity, experimental system, photosynthate transport