Considerazioni ecologiche su alcuni geofunghi e idrofunghi

Abstract

Ecological considerations on some geofungi and hydrofungi. Some ecological aspects of the terrestrial and aquatic mycoflora are preliminarily examined, emphasizing in particular the ecological relations between fungi and environmental factors. The author adds a personal contribution based on his researches on the composition of Ticino river's fungal flora, controlled monthly in and around Pavia in the years 1973 and 1974, and on the quantitative production of aflatoxin B₁ by a toxinogenic strain of Aspergillus flavus in the presence of herbicides.

Yeasts represent the main component of the fungal flora of river waters, with a prevalence of Rhodotorula (R. rubra) in winter, Candida and Geotrichum in summer. In the zones of the river where industrial or urban discharges arrive, the population of yeasts is greater than in the North and South zone of the town. The data about the population of yeasts, chiefly of the genera Rhodotorula, Sporobolomyces and Candida, prove that these fungi are good biological indicators of contamination of a waterway.

As far as aflatoxins are concerned the author points out the stimulating influence of the herbicides Pyrazon (PCA) and Diuron (DMU) on the production of aflatoxin B₁.     

Notizie ecologiche,cariologiche e sistematiche su Nepeta foliosa Moris

Abstract

Some ecological, caryological and systematic data on Nepeta foliosa Moris. – Nepeta foliosa is a rare Sardinian endemic species, which lives at an altitude of 1200 m, on the Oliena calcareous mountains in Central Sardinia. Its somatic chromosome number is 2n = 36. From a taxonomical point of view, N. foliosa appears a well isolated species within the Nepeta section, where recently Turner placed it. It shows affinity with species of the Pycnonepeta Benth. section, and particularly with Nepeta multibracteata Desf. For this reason it is here proposed to transfer N. foliosa into the Pycnonepeta section.     

Osservazioni embriologiche,sistematiche ed ecologiche su Allium parciflorum Viv.

Abstract

Embryological, systematic and ecological observations on Allium parciflorum Viv. The morphological observations and the comparison with some allied species have shown a good taxonomic isolation of Allium parciflorum: this has suggested to ascribe it to a new section.

It has been observed that the female gametophyte develops according to the disporic-type, as in other species of Allium previously studied.

The distributional area in Sardinia has been considerably extended and many ecological data are also given.     

New Insights in the Systematics of the Phyllophoraceae (Gigartinales,Rhodophyta)

The Phyllophoraceae, consisting of about 100 species worldwide, stands out in exhibiting a wide spectrum of unique life history types that makes it unusually interesting for assessing the phylogenetic importance of reproductive traits relative to classification criteria. Type of life history and position of the reproductive structures on the thallus have traditionally formed the basis for separating 11 genera in the Phyllophoraceae; however, phylogenetic analyses inferred from three sets of DNA sequences [chloroplast‐encoded rbcL, nuclear large‐subunit ribosomal RNA gene (LSU rDNA), and internal transcribed spacer regions (ITS) of nuclear ribosomal DNA], instead indicate a lack of correlation between type of life history and phylogenetic relationships among the established taxa. This lack of correlation dramatically challenges all of the traditional taxonomy, and we will present a revised classification for the family that downplays life‐history features. The study will answer the question which morphological features can be used as meaningful indicators of phylogenetic relationships in the Phyllophoraceae. The results will also be addressed in light of global biogeographic hypotheses for the family.     

Summer biomass of a population of Phyllophora antarctica (Phyllophoraceae,Rhodophyta) from Antarctica

Results of a study on summer biomass in aninfralittoral population of Phyllophora antarctica A.et E. S. Gepp from Terra Nova Bay (Ross Sea,Antarctica) are reported. The population studied grewat depths of 5 to 12 m. The highest value of biomass(1548 wet g m⁻²) was found at the end of January at6 m depth. Data showed that biomass depended mainly onthe presence or absence of large heavy specimens, eventhough these were always few in number. Moreover, thevery high number of specimens in weight classes 1 (upto 0.03 wet g) and 2 (> 0.03 to 0.06 wet g) recordedfrom December to January showed a relevant productionof new thalli in that period; the decrease of thetotal number of thalli from 8832 counted on 30December to 4384 counted on 10 February, showed someself-thinning in the population; the occurrence ofnumerous thalli belonging to weight classes 3 (>0.06 to 0.125 wet g), 4 (> 0.125 to 0.25 wet g) and5 (> 0.25 to 0.5 wet g) just at the end of December,allows to conclude that P. antarctica continues togrow, although at low rate, during the period ofwinter darkness. Finally, both the low number ofthalli of weight classes 6 (> 0.5 to 1 wet g) and 7(> 1 to 2 wet g) and the absence of thalli of theweight class 8 (> 2 wet g), recorded at the end ofDecember, indicate that most of specimens reachingduring the winter such weight classes (due to theirability to dark growth), died before summer. This revised version was published online in July 2006 with corrections to the Cover Date.     

Carrageenans from chilean samples of Stenogramme interrupta (Phyllophoraceae): structural analysis and biological activity

Carrageenans extracted from cystocarpic and tetrasporic Stenogramme interrupta were analysed by chemical and spectroscopic methods. The carrageenan from cystocarpic plants is composed predominantly of 0.5 M KCl-insoluble and 1 M KCl-soluble fractions. The insoluble fraction contained iota-carrageenan as the major component with alpha-carrageenan and pyruvated carrageenan as minor components. The soluble fraction is highly heterogeneous and did not contain the precursors mu- and nu-carrageenans. The polysaccharide from tetrasporic plants is composed of zeta- and lambda-carrageenans, and low sulfated galactans. It is soluble in KCl and partly cyclized by alkaline treatment. The antiviral and anticoagulant properties of the insoluble polysaccharide fraction from cystocarpic S. interrupta and the polysaccharide from tetrasporic S. interrupta are reported the results of which suggest promising antiherpetic activity.     

Life Cycle of Mycosphaerella brassicicola (Duby) Lindau and Ascospore Production in vitro

The germ-hyphae of the M. brassicicola ascospores penetrated the host leaves (white cabbage) 10 days after inoculation during the summer at 17 °C. The penetration occurred without exception by way of the stomata. Following a period of intercellular growth which lasted up to 15 days, brownish discolourations of the host cell walls and the destruction of mesophyll cells were observed. At this stage of infection, fruit-body primordia developed from hyaline, thick-walled, granulated mycelium, which blackend after conglomeration due to melanine deposits. The further ascocarp development was ascolocular.
Ascospore production of M. brassicicola was increased in vitro by variation of the incubation temperatures, medium-pH and irradiation. The highest sporulation rate was obtained in cultures on vegetable juice medium adjusted to pH 6, incubated at 17 °C and subjected immediately after onset of growth to 4 h UVA radiation. The percentage of germinated ascospores (70 %) corresponded to that of the dark incubated controls. Fructification and infectivity were subject to seasonal fluctuations under growth chamber conditions.     

Flora of the Isle su Cardulinu (Southern Sardinia)

Abstract

The results of two years of collection in a small isle in the southern Sardinia are reported, consisting in a floristic list of 116 entities distributed in 96 genera and 41 families. The biological spectrum of this flora puts in evidence a typical Mediterranean environment, characterized by a marked summer dryness. The ratio: number of entities/surface of the studied site has been compared with that of other small southern Sardinian islands, resulting the highest value. This floristic aspect, as well as differences in the biological spectrum, is interpreted as the result of the presence in the area under study of a desultory link with the mainland, in form of a sandy isthmus. This seems important in breaking the biological balance of the small island.     

Linkage disequilibria and the site frequency spectra in the su(s) and su(w(a)) regions of the Drosophila melanogaster X chromosome

Over the last decade, surveys of DNA sequence variation in natural populations of several Drosophila species and other taxa have established that polymorphism is reduced in genomic regions characterized by low rates of crossing over per physical length. Parallel studies have also established that divergence between species is not reduced in these same genomic regions, thus eliminating explanations that rely on a correlation between the rates of mutation and crossing over. Several theoretical models (directional hitchhiking, background selection, and random environment) have been proposed as population genetic explanations. In this study samples from an African population (n = 50) and a European population (n = 51) were surveyed at the su(s) (1955 bp) and su(w(a)) (3213 bp) loci for DNA sequence polymorphism, utilizing a stratified SSCP/DNA sequencing protocol. These loci are located near the telomere of the X chromosome, in a region of reduced crossing over per physical length, and exhibit a significant reduction in DNA sequence polymorphism. Unlike most previously surveyed, these loci reveal substantial skews toward rare site frequencies, consistent with the predictions of directional hitchhiking and random environment models and inconsistent with the general predictions of the background selection model (or neutral theory). No evidence for excess geographic differentiation at these loci is observed. Although linkage disequilibrium is observed between closely linked sites within these loci, many recombination events in the genealogy of the sampled alleles can be inferred and the genomic scale of linkage disequilibrium, measured in base pairs between sites, is the same as that observed for loci in regions of normal crossing over. We conclude that gene conversion must be high in these regions of low crossing over.     

Ecdysterone responsive functions in the mutantl(1)su(f) ts67g ofDrosophila melanogaster

Summary Transferring the temperature sensitive mutantl(1)su(f) ^ts67g from 25° C to 30° C before or early in the third larval instar blocks the increase in the ecdysterone titer that normally occurs at the end of the larval period. Feeding exogenous ecdysterone to these hormone-deficient larvae results in the formation of pseudopupae. The mutant was used to study ecdysterone-inducible functions in late larval salivary glands by preparing three animal samples with different hormone titers: the titer was low in one sample because of an earlier temperature shift, high in a second sample because the larvae were subsequently transferred to ecdysterone-supplemented food, and also high in a third sample that was kept at 25°C, providing a control for normal development. The effect of the different hormone conditions was studied by³⁵S-methionine labeling of the salivary gland proteins during the larval to prepupal transition and the prepupal period. The results indicate that synthesis of several of the proteins normally appearing during the transition and prepupal period is induced by exogenous ecdysterone.