Vegetation of trampled soil dominated by C4 plants in Europe

Abstract. Plant communities of trampled soil dominated by plants characterized by the C4-assimilation syndrome were investigated in Europe. These species, belonging to genera such as Chamaesyce, Amaranthus, Eleusine, Eragrostis and Setaria, are thermophilous, late-germinating, prostrate herbs or grasses. The centre of their distribution is in the (Sub)Tropics. A syntaxonomic revision of the phytosociological material from Europe (incl. the Macaronesian Archipelago) revealed three alliances: the Euphorbion prostratae from Spain, the Polycarpo-Eleusinion indicae from Italy, and Slovenian and Croatian Istria, and the Eragrostio-Polygonion arenastri from temperate regions of Europe. The latter two syntaxa are described as new. All three alliances belong to the order Eragrostietalia (class Stellarietea mediae). Vicarious (ecologically analogous) communities occur also in southern Africa, eastern Asia and North America. The communities studied in the present paper are considered to be an impoverished form of highly diversified trampled plant communities typical of (sub)tropical areas.     

Interactions between arbuscular mycorrhizal fungi and the hemiparasitic angiosperm Rhinanthus minor during co-infection of a host

The outcome of dual infection of the grass Lolium perenne L. by arbuscular mycorrhizal (AM) fungi and the parasitic angiosperm Rhinanthus minor L. was investigated in a glasshouse study. Colonization of L. perenne roots by AM fungi was significantly reduced by the presence of R. minor , as was host growth which fell by 44–51%. It was concluded that these two responses were linked, with AM colonization declining in response to the reduction in availability of host carbon. Parasite growth and reproductive output rose by 58% and 47% respectively when the hosts were mycorrhizal. These trends were unrelated to the attachment success of the parasite, but were accompanied by a significant increase in the formation of secondary haustoria. The benefits afforded the parasite when the hosts were mycorrhizal were attributed to increased carbon and nutrient flux resulting from alternations in sink strength. Host responses to parasitism and mycorrhizal colonization were not affected by the interaction between the two symbionts. However, the suggestion is made that the interaction between the AM fungi and parasite might have long-term ecological implications for the host species via its impact on parasite fecundity.     

Effects of egg aging on in vitro fertilization and first cleavage division in the hamster

The postovulatory fertile life of mammalian eggs is remarkably short (approximately 6-36h). Anomalies of embryogenesis may result from fertilization of aged, defective eggs. Attempts to study this problem using whole-animal models are complicated by chances in the natural milieu of the gametes. In the present study, postovulatory hamster eggs were allowed to agein vivo then fertilized in vitro. Cumulus-intact eggs recovered from superovulated hamsters either 2 or 9 h after the estiated time of ovulation (12 h postHCG) were incubated for 4 h with preincubated sperm suspentions in a modified Tyrode's solution devised for in vitro fertilization. Eggs were either fixed or cultured for another 20h in fresh medium to allow cleavage to occur, then examined by light microscopy (phase and interference-contrast). No significant difference was found in the ablities of fresh and aged eggs to be penetrated by spermatozoa (94% vs 90%, respectively; 8 replicated experiments), but only 59% of penetrated aged eggs were found to undergo morphologically normally fertilization (2 polar bodies, 2 prounclei) compared with 75% of fresh eggs (difference significant, P< 0.01). About 13% of eggs were polyspermic in both categories. The most common anomaly in aged fertilied egges was failure to extrude the second polor body (23% off eggs vs 8% of fresh eggs, P < 0.01). Only 21% of aged eggs underwent first cleavaage, and only 74% of these appeared morphologically normal, compared with value of 68% and 98%, respectively, for fresh eggs. These data show that in the hamster, abnormal fertilization and cleavage failure can, in part, be directly attributed to postovulatory deterioration of eggs. We also infer that the apparently very short penetrable life of hamster eggs in vivo shown by previous investigators is an indirect effect of postovulatory changes in the female reproductive tract that are unfavorable for sperm-egg interactions.     

Role of two phoretic mites in transmission of bluestain fungus, Ceratocystis minor

ABSTRACT.

• 1 Tarsonemus mites phoretic on southern pine beetles were shown to be hypervectors of bluestain fungus, Ceratocystis minor (Hedgcock 1906).
• 2 Beetles with phoretic mites had significantly more C.minor than did mite-free beetles.
• 3 Over 90% of tarsonemid mites collected from beetle-infested inner bark and 59% of mites phoretic on emerging beetles carried C.minor spores.
• 4 This association is an interesting example of a three-way mutualism among insects, mites and fungi.

     

Trichinella spiralis: genetic basis for differential expression of phase-specific intestinal immunity in inbred mice

Responsiveness of mouse strains after phase-specific immunization with Trichinella spiralis is compared. Two strains ($\text{NFR}\text{N, NFS/N}$) showed strong overall responsiveness. The response type could be characterized in phase-specific terms as: strongly anti-adult, weakly to moderately anti-preadult, and strongly antifecundity. By comparison, congenic mice of the C₅₇B1 $\text{10}\text{Sn}$ background (B10·A, B10·D₂, B10·S, B10·Q) displayed poor total responses that could be characterized as: weakly anti-adult, very weakly anti-preadult, weakly anti-fecundity after preadult immunization, and mixed (weak and strong) after adult immunization. The $\text{C}{}_3\text{H}\text{HeJ}$ mouse appeared to be intermediate between the B10·BR and the $\text{NFR}\text{N}$ strains in overall responsiveness. Genetic determinants of anti-preadult or anti-adult responses of $\text{NFR}\text{N}$ strain mice were dominant over their B10 congenic counterparts as shown in F₁, crosses of $\text{NFR}\text{N}$ × B1O·BR mice. Since the $\text{NFR}\text{N}$ (predominantly H-2^q) and the $\text{NFS}\text{N}$ (H-2^S) are both strong responders, while the B10·Q(H-2^q) and B10·S (H-2^S) are weak, it is suggested that the major genes controlling anti-preadult and anti-adult responses are not linked to the major histocompatibility complex. However, variations in anti-adult immunity and anti-fecundity in the B10 congenic mice (B10·Q and B10·S are the strongest responders) suggest that minor genes linked to the MHC exert some control over these responses. Some evidence was obtained for gene complementation as the F₁ cross of $\text{NFR}\text{N}$ and $\text{NFS}\text{N}$ mice responded more vigorously than the parental lines. We conclude that multiple genes determine anti-T. spiralis intestinal responses in mice. The major genes are unlinked to the major histocompatibility complex whereas several minor genes are linked.     

Changes in the content of modified nucleotides of total transfer RNA of wheat seedlings during greening

The contents in minor nucleotides of total transfer RNA (tRNA) of etiolated and light-grown wheat (Triticum aestivum L.) seedlings and of seedlings illuminated for 24 or 48 h were examined. The total tRNA of seedlings illuminated 24 h contained more, and that from seedlings illuminated 48 h still more modified nucleotides than that from etiolated ones. Thus, the appearance of the characteristic minor nucleotides of tRNA of light-grown wheat seedlings needs a rather long greening period, of at least 48 h.     

Physico-chemical environment in Tjeukemeer with special reference to speciation of algal nutrients

This paper attempts to generalize the major controlling factors and their impacts on the physico-chemical environment in Tjeukemeer in relation to the speciation of algal nutrients.Morphometry, man-made hydrology, climate, chemistry of drainage area and biology of the lake appear to control its physico-chemistry the most. Thus the shallow Tieukemeer is vulnerable to wind and therefore almost always completely mixed and often turbid owing to resuspended sediments. In normal summers the lake is oligohaline, hard, eutrophic and alkaline, and in winter it is hard, eutrophic, alkaline and humus-rich. The implications of these properties on the following physico-chemical components and their relevance for the speciation of algal nutrients are discussed: turbidity, colour, halinity, pH, alkalinity, salinity, conductivity, ionic composition, ionic balance and organic matter.Because of the relationships between the physico-chemical environment on the one hand and the speciation and bio-availability of nutrients on the other hand, special attention is given to the speciation of some major and minor elements as derived from ultra filtration experiments. In this context, the metal binding capacity of the organic matter (mainly fulvic acids) is also considered.     

Variations during leaf development of the relative amounts of two bean (Phaseolus vulgaris) chloroplast tRNAsPhe which differ in their minor nucleotide content

Bean (Phaseolus vulgaris cv. Saxa) chloroplasts contain two tRNA^Phe species, namely tRNA^Phe1 and tRNA^Phe2. By sequence determination, we show that tRNA^Phe2 is identical to the previously sequenced tRNA^Phe1 except for two undermodified nucleotides. By reversed-phase chromatography analyses, we demonstrate that the relative amounts of these two chloroplast tRNAs^Phe vary during leaf development: in etiolated leaves the undermodified tRNA^Phe2 only represents 15% of total chloroplast tRNA^Phe, during development and greening it increases to reach 60% in 8-day-old leaves, and it then decreases to 9% in senescing leaves.