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.     

Photosynthetic Changes in the Inducible CAM Plant Sedum telephium L Following the Imposition of Water Stress. II. Changes in the Activity of Phosphoenolpyruvate Carboxylase

In Sedum telephium, the switch from a weak-CAM to a full-CAMmode of photosynthesis in response to water stress, is accompaniedby a marked increase in the activity of the enzyme phosphoenolpyruatecarboxylase (PEPC) during the dark period of a diurnal cycle.Fractionation of the enzyme by non-denaturing polyacrylamidegel electrophoresis gives two active species; the activity ofthe more mobile species increases with the switch into a full-CAMmode of photosynthesis. Fractionation of the enzyme by denaturing electrophoresis andby gel filtration indicates that the molecular species particularlyactive in CAM is a monomeric protein, whilst the other readilyobservable species is a dimer. Sedum telephium, CAM, water stress, phosphoenolpyruvate carboxylase, night-time activation dimer, monomer     

Enzymic Activities Associated with the Ability of Aerial and Submerged Forms of Littorella uniflora (L.) Aschers to perform CAM

ABSRACT: Groenhof, A. C, Smirnoff, N. and Bryant, J. A. 1988. Enzymicactivities associated with the ability of aerial and submergedforms of Littorella uniflora (L.) Aschers to perform CAM.—J.exp. Bot. 39: 353-361. The submerged form of Littorella uniflora shows a full CAM modeof photosynthesis as shown by diel acid fluctuations and elevatedactivities (in comparison to non-submerged leaves) of the enzymesphosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme.Non-submerged plants exhibit no diel fluctuations of acidityand no changes in activity of NADP-malic enzyme or PEPC. PEPCactivity is low and NADP-malic enzyme is not detectable. Furthercharacterization of PEPC extracted from submerged plants duringthe light and dark periods of a diel cycle shows that the enzymeextracted in the dark is more active. In addition, the enzymeshows a decrease in K_m (PEP) and an increase in V_max in thepresence of glucose-6-phosphate, whilst in the presence of malateK_m (PEP) is increased and V_max decreased; this response to malateis only observed in the light and at pH 7.2. Molecular weightdeterminations using a Sephacryl S-300 column show that theenzyme extracted from plants during the dark period has an apparentmol. wt. of 375 KDa and the enzyme extracted from plants duringthe light period has an apparent mol. wt. of 307 KDa. Key words: Littorella uniflora (shoreweed), Crassulacean acid metabolism, PEP carboxylase, malic enzyme     

Coccidian Parasites (Apicomplexa: Eimeriidae) from Insectivores. V. Ten Forms from the Moles of Japan (Euroscaptor,Mogera spp.)1

ABSTRACT. Moles from Japan were examined for coccidian oocysts, and 67 of 77 (87%) hosts were infected including 8 of 11 (73%) Euroscaptor mizura, 31 of 36 (86%) Mogera kobeae, 17 of 17 M. tokudae, and 11 of 13 (85%) M. wogura. Of 67 infected hosts, 57 (85%) had multiple infections representing 2–5 coccidian species when examined. All oocysts in the infected fecal samples remained unsporulated and the absence of sporulation may be the result of storing feces from Japanese moles in 2% aqueous H₂SO₄. Five structurally distinct forms of unsporulated oocysts were found in E. mizura, and five distinct forms of unsporulated oocysts were also seen in Mogera spp. Two of the forms from E. mizura were similar to forms from Mogera spp., and the five forms from Mogera were shared freely between the three Mogera species. This is the first systematic survey of Japanese moles for coccidia.     

Energetics of the annual cycle of Dippers Cinclus cinclus

Time-activity budgets and energy expenditure of Dippers Cinclus cinclus were studied in all months of the year and for every stage of the annual cycle. The commonest daytime activity was feeding (54%), then resting (43%) and flying (4%). On a 24-hr day basis the most marked changes in activity followed from changing daylengths. DEE (Daily Energy Expenditure), derived from time-activity budgets through the year and laboratory estimates of metabolism, averaged 201 kj d ^-1 in females and 228 kj d ^-1 in the larger males. Over a more restricted range of circumstances, direct estimates of DEE obtained from 77 Dippers using the doubly labelled water technique averaged 205 ± 43 kj d^-1 and 251 ± 55 kj d^-1 in females and males, respectively. Overall, the correspondence between these largely independent estimates of energy expenditure was reasonably close. DEE was highest during breeding (laying-females; rearing-males) and in late winter for both sexes. The lowest energy expenditures occurred during moult, amongst juveniles and in early winter. Incubating females and mate-guarding males also had low energy costs. Across all stages of the annual cycle body size, activity patterns, ambient temperature and river flow had significant effects on energy expenditure. The rate at which food was gathered to meet these changing energy demands varied widely. While some of this variation was imposed by a seasonal environment, it was also likely to reflect adaptive shifts in rates of food gathering, in some cases consequent upon the changing fitness benefits of various non-feeding activities.     

Aminopeptidases from Plasmodium falciparum, Plasmodium chabaudi chabaudi and Plasmodium berghei

ABSTRACT. Using fluorogenic substrates and polyacrylamide gels we detected in cell-free extracts of Plasmodium falciparum, Plasmodium chabaudi chabaudi and Plasmodium berghei only a single aminopeptidase. A comparative study of the aminopeptidase activity in each extract revealed that the enzymes have similar specificities and kinetics, a near-neutral pH optima of 7.2 and are moderately thermophilic. Each has an apparent molecular weight of 80,000 ± 10,000, determined by high performance liquid chromatography on a calibrated SW500 column. Whilst the P. c. chabaudi and P. berghei activity co-migrate in native polyacrylamide gels, that of P. falciparum migrates more slowly. The three enzymes can be selectively inhibited by ortho -phenanthroline and are thus metallo-aminopeptidases; however, in contrast to other aminopeptidases the metal co-factor does not appear to be Zn²⁺.