Nitrogen Mobilization from Stubble and Roots during Re-growth of Defoliated Perennial Ryegrass

Nitrogen re-mobilization during ryegrass (Lolium perenne L.)re-growth was studied as a function of time. Roots and stubblecompounds were labelled with ¹⁵N before clipping. Experimentalresults clearly showed that ryegrass re-growth involves twoperiods of differing physiological significance. The first occursduring the first 6 d when nearly all the nitrogen of the newleaves comes from organic nitrogen re-mobilized from roots andstubble. At the same time, the uptake of nitrogen from the mediumis very low, no reduction of endogenous nitrate occurs and proteolysisand amino amido nitrogen re-mobilization in stubble are notfully compensated for by synthesis.Thus, the change in protein-Ncontent, expressed per plant, in stubble decreases from 998µg (uncut plant) to 866 µg and 661 µg for2 d and 4 d respectively after cutting. The second period (afterthe sixth day) may be more representative of stable behaviourof ryegrass, with assimilation of mineral nitrogen from themedium providing the predominant source of nitrogen for re-growth. Key words: Lolium perenne L., nitrogen, re-growth     

The life cycle of Hydrichthys tnirus (Gnidaria: Hydrozoa: Anthomedusae: Pandeidae)

The previously unknown life cycle of the parasitic hydroid Hydrichthys mirus is described. The adult medusa has 5–6 tentacles and could be referred to Leuckartiara. Another species of Hydrichthys has previously been shown to have a Stomotoca -like medusa, characterized by the possession of two tentacles. It is proposed that Hydrichthys originated from the Leuckartiara lineage and that, through paedomorphosis in at least one species, the medusa retained the two-tentacle state of the newly-released medusa of all pandeids, thus becoming referable to Stomotoca. It is suggested that Stomotoca has hitherto constituted a polyphyletic taxon, embracing parallel lineages of pandeids, each retaining juvenile features. An additional genus, Larsonia , is introduced to accommodate species with Stomotoca-like medusae and Hydrichthys -like hydroids.     

Facts and Hypotheses Concerning the Control of Odontoblast Differentiation

Numerous studies using amphibians have demonstrated that preodontoblasts emerging from the dental papilla are derived from cranial neural crest cells [4, 12, 46, 64]. However this has not been established for mammals. The history of odontogenesis begins during the early stages of cranial-facial development when the maxillary and mandibular processes develop. Continuous epithelio-mesenchymal interactions condition the histogenesis and morphogenesis of the teeth [24–26, 43, 44, 49, 51,58] as well as the terminal differentiation of odontoblasts and ameloblasts [23, 47, 52, 54, 59, 61, 67].
During recent years a considerable amount of experimental data relating to differentiation of odontoblasts has been published. We summarize these data and attempt to integrate them in deductive hypotheses concerning the control of odontoblast differentiation.     

La Genèse des Mérozoïtes chez la Coccidie Eimeria necatrix. Etude Ultrastructurale*

RESUME. Les schizontes de 2 ème génération d'Eimeria necatrix ont étéétudiés au microscope électronique. La différenciation des mérozoïtes est associée à la dernière mitose, qui ne semble pas différer essentiellement des précédentes. Les mérozoïtes se développent à la périphérie du schizonte. Le conoide et 22 microtubules sous pelliculaires, probablement induits par les centrioles, et le complexe membranaire interne ainsi que les précurseurs des rhoptries, qui semblent issus de l'appareil de Golgi, apparaissent auprès de chaque pôle nucléaire, sous la membrane du schizonte. Ces organites sont les premiers inclus dans les ébauches de mérozoïtes. Puis, le noyau, le dictyosome et les vésicules multimembranaires pénètrent dans les futurs mérozoïtes. Les micronèmes, probablement formés par l'appareil de Golgi, et les grains d'amylopectine sont produits plus tard, quand les mérozoïtes se séparent du reliquat cytoplasmique. Le mode de genèse de ces divers organites et les relations entre le dernière mitose et la différenciation sont discutés. SYNOPSIS. Second generation schizonts of Eimeria necatrix were studied with the aid of the electron microscope. Differentiation of daughter merozoites is associated with the last mitosis, which is not significantly different from the earlier ones. The merozoites develop at the periphery of the schizont. The conoid and 22 subpellicular microtubules, probably induced by centrioles, and the inner membranes complex and the rhoptry anlagen which seem to be produced by the Golgi apparatus, appear close to each nuclear pole, just near the schizont membrane. These organelles are the first to appear in the merozoite anlagen. Then, nucleus, dictyosome and multimembranous vesicles enter the budding merozoites. Micronemes, probably originating from Golgi apparatus, and amylopectin granules are produced later, when daughter merozoites separate from the residuum. The genesis of these various organelles and the relation between the last mitosis and differentiation are discussed.     

NADH and NADPH Dependent Malate Dehydrogenases of Phaseolus vulgaris

French bean (Phaseolus vulgaris L. cv. Contender) leaf extracts catalyse the reduction of oxaloacetate to malate in the presence of NADH and NADPH. Under the experimental conditions used, the optimum pH values are 8 and 6 respectively. After chromatography on diethylaminoethyl cellulose, two principal forms of NADH-MDH (L-malate: NAD⁺ oxidoreductase, E.C. 1.1.1.37) upon which NADPH activities are superposed, can be characterized. This result is confirmed by electrophoresis on polyacrylamide gel. On the other hand, after filtration on Ultrogel 34, NADH-MDH is eluted as a single peak; once again, NADPH activity is associated with it. When PtCl^2?₄, a powerful inhibitor of MDH, is added to the reaction medium, the degree of inhibition is the same irrespective of the cofactor employed. When root extracts are submitted to chromatography on diethylaminoethyl cellulose, activity profiles are identical to those obtained with leaves. These results suggest that the NAD dependent enzymes can also utilize NADP to reduce oxaloacetate. After addition of dithiothreitol, another NADPH-MDH activity manifests itself in the leaf extracts; it differs from the foregoing ones in its optimum pH, its chromatographic properties and its response to PtCl^2?₄ action. Root extracts do not exhibit this activity thus showing a specific localization of this enzyme in the green part of the plant.     

Diagnosing the environmental causes of the decline in Grey Partridge Perdix perdix survival in France

We studied Grey Partridge Perdix perdix mortality during breeding to identify the environmental causes of a long‐term decline in adult survival. We radiotagged and monitored daily from mid‐March to mid‐September 1009 females on ten contrasting study sites in 1995‐97. Simultaneously, we recorded habitat features and estimated the abundance of Hen and Marsh Harriers Circus cyaneus and C. aeruginosus Red Fox Vulpes vulpes and mustelids. We experimentally tested whether scavenging could have biased predation rates. We also examined, through the necropsy of 80 carcasses of Grey Partridge, whether disease, parasites or poisoning could have been ultimate causes of high predation rates. The survival rate of radiotagged females during spring and summer ranged from 0.25 to 0.65 across study areas. Mortality peaked in May, June and July when females were laying and incubating. The direct negative impact of farming practices was low (6%). Predation was the main proximate cause of female mortality during breeding (73%) and determined the survival rate, suggesting no compensation by other causes of mortality. Ground carnivores were responsible for 64% of predation cases, and raptors for 29%, but this proportion varied across study sites. Disease and poisoning did not appear to favour predation, and scavenging was not likely to have substantially overestimated predation rates. The predation rate on breeding females was positively correlated with the abundance of Hen and Marsh Harriers, suggesting an additional mortality in areas where harriers were abundant. The proportion of raptor predation was linearly related to harrier abundance. The predation rate was not correlated with the abundance of the Red Fox and mustelids. A potential density‐dependent effect on the predation rate was confounded by the abundance of harriers. We found no convincing relationship between the predation rate and habitat features, but we observed a positive relationship between the abundance of Hen and Marsh Harriers and the mean field size. This suggested that habitat characteristics may contribute to high predation rates through predator abundance or habitat‐dependent predation.     

Updating the Trachelocercids (Ciliophora, Karyorelictea). I. A Detailed Description of the Infraciliature of Trachelolophos gigas N. G., N. Sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) N. Comb

ABSTRACT. Trachelolophos gigas n. g., n. sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) n. comb. (basionym: Tracheloraphis filum) were discovered in the mesopsammon of the French Atlantic coast at Roscoff. Their morphology and infraciliature were studied in live and protargol impregnated specimens. The new genus, Trachelolophos, belongs to the family Trachelocercidae and is unique in having a conspicuous ciliary tuft, which is very likely a highly modified brosse, in the oral cavity. The two species investigated have a very similar infraciliature, differing only in morphometric characteristics and in the nuclear configuration. The entire somatic and oral infraciliature consists of dikinetids which have both basal bodies ciliated or only the anterior or posterior ones, depending on the region of the cell. The right side is densely and uniformly ciliated. Its kineties extend onto the left side to the glabrous stripe, where an anterior and posterior secant system are formed, reducing the number of kineties in the narrowed neck and tail region. The left side bears a narrow glabrous stripe bordered by slightly irregularly arranged dikinetids having rather stiff cilia (bristles), possibly forming an uninterrupted, prolate ellipsoidal (bristle) kinety as indicated by their ciliation. The bristle kinety commences subapically at the right margin of the glabrous stripe, extends posteriorly, then anteriorly at the left, to end up at the right margin again. The dikinetids of the right posterior portion of the bristle kinety have the posterior basal bodies ciliated, whereas the anterior basal bodies are ciliated in its left and right anterior portion. The ends of the bristle kinety meet distinctly subapically at the right margin of the glabrous stripe, as indicated by the diametrically opposed ciliation of the dikinetids. The anterior region (head) of the cell bears a distinct circumoral kinety composed of very regularly arranged dikinetids, associated with nematodesmata forming an oral basket together with the nematodesmal bundles originating from the oralized somatic dikinetids at the anterior end of the somatic kineties. The systematics of trachelocercid ciliates are briefly reviewed and discussed.