ALBERT

Notes: 1. Tracer experiments with two diatoms labelled with 13C (Nitzschia palea) and 15N (Fragilaria crotonensis), were conducted to investigate feeding selectivity and interspecific competition between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and estimated biovolume, were used first to detect feeding preferences within the different grazer treatments.2. The results revealed a significant decline in algal biovolume in all grazer treatments and no indications of active selectivity were observed. In contrast to conventional methods, measurements based on isotope signatures showed strong differences in tracer uptake, thus indicating different degrees of assimilation and digestion by the two grazers.3. The selectivity index Q, which provides information on the uptake ratio of 13C to 15N, showed a significant time effect for both grazer species and a significant difference between single- and mixed-grazer treatments for P. antipodarum. Thus, this technique enabled the direct quantification of the uptake by grazers and, therefore, served as an ideal tool for the detection of passive selectivity.4. Our results indicate a shift in feeding preferences related to between-species competition and a potential divergence of trophic niches when species coexist.

Notes: Abstract. The promoter of the nit1 gene, encoding the predominantly expressed isoform of the Arabidopsis thaliana (L.) Heynh. nitrilase isoenzyme family, fused to the β-glucuronidase gene (uidA) drives β-glucuronidase expression in the root system of transgenic A. thaliana and tobacco plants. This expression pattern was shown to be controlled developmentally, suggesting that the early differentiation zone of root tips and the tissue surrounding the zone of lateral root primordia formation may constitute sites of auxin biosynthesis in plants. The root system of A. thaliana was shown to express functional nitrilase enzyme. When sterile roots were fed [2H]5-L-tryptophan, they converted this precusor to [2H]5-indole-3-acetonitrile and [2H]5-indole-3-acetic acid. This latter metabolite was further metabolized into base-labile conjugates which were the predominant form of [2H]5-indole-3-acetic acid extracted from roots. When [1-13C]-indole-3-acetonitrile was fed to sterile roots, it was converted to [1-13C]-indole-3-acetic acid which was further converted to conjugates. The results prove that the A. thaliana root system is an autonomous site of indole-3-acetic acid biosynthesis from L-tryptophan.

Notes: Summary Eighty species of multicellular algae were observed in fifty-three samples, collected at six sampling stations in a ditch near the village of Tienhoven (The Netherlands) in August 1975. Most species seemed to prefer particular sampling stations above particular substrates. This preference was not observed with the algae, growing in floating and submerged algal masses. Average linkage cluster analyses from Sørensen similarity coefficients revealed a linear arrangement of the sampling stations reflecting the actual arrangement of the stations in the ditch.

Notes: Summary Artificial substrates are used for quantitative studies on production and patterns of benthic algae (HERDER-BROUWER, 1975; KLAPWIJK, 1978; and others). The method permits a quantitative approach by weighings or direct countings under the microscope. Such applications, however, imply suppositions on the homogeneity and representativity of the developed growths (TIPPETT, 1970). Observations in natural growths of algae (HILLEBRAND, 1977) indicate that spatial inhomogeneities (patterns) occur at different sampling scales. The present study deals with patterns at three levels on glass microscopy slides (26×76 mm) in floating perspex racks immersed in two eutrophic and rather unpolluted water bodies: the small pond Hortusvijver in Amsterdam (see HERDER-BROUWER, 1975) and the artificial lake Grote Maarsseveense Plas near Utrecht. The sampling levels included „micro”-distribution with 12 sectors on a single slide (3×4 in width/length partition), „meso”-distribution with 12 slides in a floating rack, and „macro”-distribution with a series of 10 racks. Micro- and mesodistribution were studied in the Hortusvijver, meso- and macrodistribution in the Grote Maarsseveense Plas. Countings of algae were made in randomly chosen fields of view under the microscope with known area. In most cases ca. 20 fields were counted at a magnification of 400x, covering ca. 1mm2 for each observational unit. Microdistribution was studied on slides immersed two weeks in August–September 1976 in the Hortusvijver. On a slide 5 sectors were chosen at random out of 12. In each of these sectors 10 countings were made in random chosen fields, resulting in 50 countings for a slide. Dominant and subdominant species (mostly diatoms) showed an aggregated (clustered) pattern. The less common, filamentous green algae and Chlorococcales occurred in a random pattern. Statistical evidence, however, of this random pattern is not possible, as the probability distribution known as negative binominal fits at low densities random as well as aggregated patterns. So it is possible that the random pattern (as it fits to a Poisson distribution) of these organisms is in fact aggregated with a low density. We concluded that the development of algal growth on a glass slide is unequal, so a sufficient number of countings is needed for a reliable description of algal density and pattern. There are great differences between glass slides within one rack (length 50 cm, mesodistribution). This was observed in winter in the Hortusvijver and in early spring (March 1977) in the Grote Maarsseveense Plas after three weeks of immersion. The dominant species (all diatoms) showed aggregation in comparisons between the glass slides, so it can be concluded that a single slide is not representative for a sampling station. Densities varied less within a glass slide than between the slides. Macrodistribution was studied in the Grote Maarsseveense Plas in March with ten racks of slides, 50 m apart from each other in a single series along the straight and relatively homogeneous SW bank with a reed vegetation. This location was chosen because of the apparent lack of environmental gradients. Even at high numbers of counted fields of vision aggregation occurred in the species with high densities (all diatoms). Differences between the racks proved to be greater than within the racks. A single rack is therefore not representative for a rather homogeneous waterbody. It was concluded that aggregation was highest at the level of macrodistribution and lowest at the level of microdistribution, but it occurred at all of the three levels and in all dominant species. Estimates of the production or the biomass of algae based on observations with artificial substrates are only reliable if the patterns of the involved (dominant) species are thoroughly described. High differences are observed between substrates from different locations in a apparently homogeneous environment, so studies of gradients are only relevant if the requirements of good quantitative work are fulfilled. Probably scraping the algae off the substrates and through suspension are required for the study of representative samples. As natural substrates are often less homogeneous than artificial ones, quantitative work with such substrates must be considered with even more caution.

Notes: Summary 1. Filamentous freshwater algae offer characteristic problems in ecological studies. Identification is often hampered by the lack of characteristic structures, mostly connected with sexual reproduction. 2. Two solutions to this problem are given. First, extended sampling in the field often provides the required structures. Secondly, culturing in the laboratory may offer satisfactory results. 3. Estimation of quantities of several species in a growth of filamentous algae in some cases has to be limited to recognition of presence or absence. 4. Filamentous algae are good indicators for the environmental circumstances and may be used in water pollution control. Well-known saprobity systems however have to be adapted to stagnant water bodies.

Notes: Summary The number and the diameters of glial cell nuclei are measured in paraffin sections through the corpus callosum of 15 cats ranging in age between 2 days and 11 years. It was found that: 1. During the first weeks of postnatal life, the number of neuroglial nuclei increases from 62 (± 9) to 229 (± 13) in a given volume, i.e. (100 μ)3, of white matter. Between the end of the first month and the eighth month the number of nuclei decreases again. In the adult cat it is 141 (± 14). 2. The decrease in the number of nuclei in a given volume is related to myelination because there is a rapid increase in the volume of fibre material between the perikarya of the glial cells. 3. The changes in nuclear size and shape associated with the increase in the number of cells can be investigated quantitatively by measuring the diameters of individual nuclei and by computing their volume. It is shown that the oblong nuclei of very young cats have a volume of about 70 μ3. In older animals, larger nuclei appear which are oval -and have a mean volume of more than 100 μ3. In the adult cat, the nuclei are round and their mean volume is about 50 μ3. The possible cause of the differences in nuclear volume of glial cells during postnatal development of white matter is discussed.

Notes: Summary The corpus callosum has been investigated in paraffin sections through the brains of cats fixed at various ages by perfusion with Bouin's fluid via the aorta. During the first few weeks of postnatal life numerous mitoses have been found, and there is an enormous increase in the number of neuroglial cells. Apart from the multiplication of glial cells there are impressive changes in their histological features such as the size and shape of the cell nucleus and the stainability of the cytoplasm. The multiplication of neuroglial cells and the changes in their appearance resemble the “Myelinisationsgliose” which was described in the human brain by Roback and Scherer in 1935 but which has since been forgotten. The term “Myelinisationsgliose” is misleading and should be abandoned because the multiplication of glial cells in conjunction with myelination is not a pathological phenomenon but a constant feature in the postnatal development of the brain. It is pointed out that the postnatal changes in the neuroglia of white matter should be taken into consideration when attempts are made to interpret certain physiological, pathological, and pharmacological findings in the infant brain.