Abundance of protein-bound sulfhydryl and bisulfide groups at chromosomal nucleolus organizing regions

Silver stainability of the chromosomal nucleolus organizing regions that contain the structural genes for ribosomal RNA can be abolished by proteolytic and oxidative treatments. Histone extraction has no effect. This indicates that reducing groups of non-histone chromosomal proteins are responsible for silver staining. Treatment with fluorescent sulfhydryl and disulfide specific reagents followed by silver staining demonstrates coincidence of silver dots and brightly fluorescent spots at the short arms of human acrocentric chromosomes where ribosomal RNA-genes are located. After treatment with cupric sulfite reagent in the presence of urea fluorescence and silver staining was no longer possible. Silver staining has been reported to be associated with ribosomal RNA-gene activity. Acrocentric chromosomes that are negative in silver staining also lack the brightly fluorescent spots. Therefore, we conclude that an abundance of protein-bound sulfhydryl and disulfide groups occur at nucleolar organizing regions with active genes. Differentially fluorescing spots could not be observed after staining with fluorescamine. So, either the sulfhydryl reagents used in this study are much more sensitive than fluorescamine to study protein distributions in cytological preparations, or our observations point to a local accumulation of some specific protein(s) rich in sulfhydryls. The presence of many sulfhydryl and disulfide groups at the nucleolus organizing regions seems suggestive of a great flexibility of protein(s) by transition of sulfhydryl groups to disulfide bridges and vice versa at these highly active regions of the genome.     

A simple mathematical model of the secondary succession of shrubs

A simple simulation model of the secondary shrub succession has been elaborated on the grounds of primary field data from abandoned fields of different ages in the area of Bohemian Karst. The model describes vegetational dynamics using adaptedVolterra-Lotka equations for competing species. Carrying capacities and growth rates are expressed as a function of the depth of the soil.     

Historical phytoplankton data of the Marsdiep

Published and unpublished data on phytoplankton of the Marsdiep tidal inlet were studied. Most older data, going back to 1897, are based on net-phytoplankton only, the earliest quantitative (Utermöhl) data being from 1965.Phaeocystis sp. bloomed in the Marsdiep after a spring diatom peak, at least as long ago as 1897. Summer or automn peaks ofPhaeocystis sp., frequent now, were also observed in 1898 and 1899. The duration of thePhaeocystis blooms in 1897 to 1899 was shorter than observed after 1978, but longer than in the early 1970s. The recent (1987 to 1989) duration ofPhaeocystis blooms is 2 to 3 times that of 1897–1899. This increase surpasses normal yearly variation and can be related to anthropogenically caused in crease in nutrient concentrations. A number of diatomspecies, at present numerically dominant in the spring peak, are not mentioned as dominant in the earlier periods of observation. They are small and passed through the nets used.Biddulphia sinensis, at present often abundant, is an immigrant in the North Sea since 1903, and for that reason absent from the earliest Marsdiep observations. No clear trend in duration of diatom blooms is apparent during 1965 to 1989. Anthropogenic eutrophication did not affect diatom blooms. Marsdiep records in the literature ofPhaeocystis globosa, P. pouchetii andP. sp. all refer to the same species.     

First record of Crustacea Malacostraca from fresh waters in the Canary Islands

Crustacea Malacostraca were hitherto unknown from fresh waters of the Canary Islands. A new species of Amphipoda, Rhipidogammarus rheophilus, has recently been discovered in springs and spring brooks in Tenerife.

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Resumen Crustacea Malacostraca era hasta ahora desconocida de las aguas dulces de las Islas Canarias. Una nueva especie de anfípodo, Rhipidogammarus rheophilus, ha sido recientemente descubierto de fuentes y manantiales de Tenerife.

     

Biotic and abiotic factors determining the distribution of two prawn species: Palaemon adspersus and P. squilla

Summary The reasons behind the absence of the prawn Palaemon adspersus and the presence of P. squilla in rockpools and on bare sand bottoms were studied. Some maximal abundances in different habitats are given. Introduction experiments into natural and artificial rockpools and measurements of tolerance towards low oxygen levels showed that nocturnal hypoxia excluded P. adspersus which was significantly more sensitive to oxygen depletion. Respiration rates measured by the closed-bottle method showed no interspecific difference.On bare sand bottoms P. aspersus was probably excluded by predators, since predator exclusion experiments in cages and predator inclusion experiments in containers showed that P. adaspersus was more vulnerable to predation than P. squilla.The costs for being able to cope with a wide array of habitat in P. squilla are probably balanced by the benefits of access to habitats such as intertidal rockpools, very shallow bottoms and deeper sand bottoms. Tolerance towards abiotic factors extends its habitat range upwards into shallower waters, and tolerance towards biotic factors, i.e. predation, extends it downwards.     

Palynological study of a holocene peat and a miocene coal deposit from NW Borneo

The development of a Holocene peat near Marudi (Sarawak) and a Miocene coal near Berakas (Brunei) is studied pollen-analytically and stratigraphically by comparison with present-day swamp vegetation along the NW Bornean coast. A number of 76 pollen and spore types were recognized and are briefly diagnosed.The Marudi profile starts on mangrove sediment and shows a succession which is closely comparable to the present-day zonation of the large raised bog of which it forms part.The Berakas profile starts on fluviatile sediments and remains in the mixed swamp forest stage. This small deposit has remained close to the coast and peat growth is terminated by marine transgression.The floristic composition of the mixed swamp forest stage in both bogs, separated in age by approximately seven million years is closely comparable. Minor differences which exist can be attributed to differences in size, ecologic conditions and accessibility from mainland reservoirs.Only on spore type, Stenochlaena areolaris has become extinct in Borneo.