Trace metal chemistry of a Dutch reservoir, the Tjeukemeer

SUMMARY.

• 1 The concentrations of total and dissolved (<0.2 μm) Fe, Mn, Cu, Co, Zn and Al in the Dutch reservoir, the Tjeukemeer, were recorded fortnightly between 1984 and 1986.
• 2 Due to its reservoir function, the Tjeukemeer receives water that is relatively rich in Fe and Mn from its peaty drainage area in winter. In summer, water that is relatively rich in Cu and Zn from lake IJsselmeer, which is flushed by a tributary of the River Rhine, flows into the lake. Therefore trace metal loads, as estimated from annual mean concentrations and hydraulic data, are climate-dependent.
• 3 In wet years, such as 1985, the annual Fe, Mn, Cu and Zn loads may be 3.1,0.2,0.001 and 0.009 gm^?2, respectively. In dry years, such as 1984 and 1986, the Fe and Mn loads may be less than one quarter while the Cu and Zn loads may double. Especially in wet years comparable Cu and Zn inputs occur by deposition.
• 4 Despite the dependence of trace metal loads on the climate-dependent water regime. Principal Component Analysis indicated no strong relation between the total Cu, Co, Zn and Al concentrations in lake water and hydrological tracers such as Cl^? and UV absorbance. Instead, wind speed appeared to be more strongly connected with the dynamics of these metals. Thus in the shallow Tjeukemeer, internal trace metal loading due to wind-induced resuspension starts to dominate the contributions of external loads to the total metal concentrations at wind speeds exceeding 3ms^?1.

     

Melanosome Capping of Keratinocytes in Pigmented Reconstructed Epidermis – Effect of Ultraviolet Radiation and 3‐Isobutyl‐1‐Methyl‐Xanthine on Melanogenesis

Reconstructed pigmented epidermis was established by co‐seeding autologous melanocytes and keratinocytes onto a dermal substrate and culturing for up to 6 weeks at the air–liquid interface. Inspection of the tissue architecture revealed that melanocytes are regularly interspersed only in the basal layer and transfer melanosomes to the keratinocytes. We report for the first time, the in vitro formation of supranuclear melanin caps above the keratinocyte nuclei. The formation and abundance of these melanin caps could be enhanced by pigment modifiers such as ultraviolet light and 3‐isobutyl‐1‐methyl‐xanthine (IBMX). In untreated cultures, the capping was observed in the spinous layers after 6 weeks of culture, whereas after irradiation or supplementation of the culture medium with IBMX, the capping occurred already in the basal layer 2 weeks after initiation of the stimulus. In this study, we show that IBMX and ultraviolet irradiation stimulate pigmentation via different mechanisms. After supplementation of the culture medium with IBMX the increase in pigmentation was entirely due to the increase in melanocyte activity as observed by increased dendrite formation, melanin production and transport to the keratinocytes and was not due to an increase in melanocyte proliferation. In contrast, after UV irradiation, the increase in pigmentation was also accompanied with an increase in melanocyte proliferation as well as an increase in melanocyte activity. In conclusion, we describe the establishment of pigmented reconstructed epidermis with autologous keratinocytes and melanocytes that can be kept in culture for a period of at least 6 weeks. The complete program of melanogenesis occurs: melanosome synthesis, melanosome transport to keratinocytes, supranuclear capping of keratinocyte nuclei and tanning of the epidermis. This enables sustained application of pigment stimulators over a prolonged period of time and also repeated application of pigment stimulators to be studied.     

Histology and histochemistry of the reproductive tract of the pulmonate snail,Bulinus truncatus,with observations on the effects of castration on its growth and histology

The reproductive tract of B. truncatus was investigated histologically in order to study possible effects of castration upon the accessory sex glands. In the female part of the reproductive tract—subdivided into albumen gland, oviduct, muciparous gland, oothecal gland, uterus, vagina and bursa copulatrix—13 histochemically different secretory cell types were distinguished. The majority produce different types of (acid) mucopolysaccharides. The roles of the various parts of the female tract in the production of an egg mass were elucidated by comparing the histochemistry of the egg mass to that of the female tract; the abundance and location of the cell types were also taken into account for this purpose.

The male part appeared to contain 12 histochemically different secretory cell types. These produce mainly (phospho lipoproteins together with some polysaccharides and neutral lipids.

Castration causes an acceleration of the growth of the snails. The volumes of female (albumen gland) and male (prostate gland) accessory sex glands were measured on histological sections. It appeared that growth of the albumen gland is not arrested by castration. This was not established beyond doubt for the prostate gland. The results suggest that the stimulating effects of the dorsal body hormone on the growth and synthetic capacity of the female accessory sex glands—such effects have been established for Lymnaea stagnalis—are not exerted via the ovotestis in B. truncatus.     

Geochemical aspects of aqueous iron, phosphorus and dissolved organic carbon in the humic Lake Tjeukemeer, The Netherlands

SUMMARY. 1. The main source of P, Fe and DOC in the humic Lake Tjeukemeer is superfluous water pumped from surrounding peaty polders. Most particulate P is intracellular but almost all particulate Fe is abiotic.
2. The size and molecular weight of the P, Fe and DOC (mainly fulvic acids (FA)) were determined by ultrafiltration and Sephadex G-100 gel filtration. Throughout the year most dissolved P and Fe was in colloids >35 nm with apparent molecular weight between 30,000 and 150.000. The bulk of FA occurred in particles <35nm.
3. Calculating the atomic ratios of P, Fe and organic C in the different size classes revealed that Fe-FA chelates are a minor species of the Fe pool. Less than 10% of the fulvic acids occurred as Fe-FA chelates.
4. Based on their apparent size and molecular weight, the Fe-FA chelates are colloidal aggregates, probably with the formula Fe_n-1(FA)_n.
5. About 50% of the dissolved P had the same size as the Fe-FA aggregates. These aggregates were only noticeable in winter when humus-rich polder water was flushed through the lake. During the rest of the year the dissolved Fe and P consisted mainly of acid-labile inorganic colloids which might have been organically coated.     

Logistics of water and salt transport through the plant: structure and functioning of the xylem

The xylem is a long‐distance transport system that is unique to higher plants. It evolved into a very sophisticated plumbing system ensuring controlled loading/unloading of ions and water and their effective translocation to the required sinks. The focus of this overview will be the intrinsic inter‐relations between structural and functional features of the xylem. Taken together the xylem is designed to prevent cavitation (entry of air bubbles), induced by negative pressures under transpiration and to repair the cavitated vessels. Half‐bordered pits between xylem parenchyma cells and xylem vessels are on the one hand the gates to the vessels but on the other hand a serious ‘bottle‐neck’ for transport. Hence it becomes evident that special transport systems exist at the interface between the cells and vessels, which allow intensive fluxes of ions and water to and out of the xylem. The molecular identification and biophysical/biochemical characterization of these transporters has just started. Paradigms for the sophisticated mechanism of controlled xylem transport under changing environmental conditions are SKOR, a Shaker‐like channel involved in K⁺‐loading and SOS1, a Na⁺/H⁺ antiporter with a proposed dual function in Na⁺ transport. In view of the importance of plant water relations it is not surprising to find that water channels dominate the gate of access to xylem. Future studies will focus on the mechanism(s) that regulate water channels and ion transporters and on their physiological role in, for example, the repair of embolism. Clearly, progress in this specific field of research will greatly benefit from an integration of molecular and biophysical techniques aimed to understand ‘whole‐plant’ behaviour under the ever‐changing environmental conditions in the daily life of all plants.     

Accidental importation of the mosquito Aedes albopictus into the Netherlands: a survey of mosquito distribution and the presence of dengue virus

Abstract.  In the summer of 2005, the Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae) was found for the first time in the Netherlands. It was collected on the premises of several horticultural companies that import the ornamental plant Dracaena sanderiana (Sparagalus: Dracaenaceae [Agavaceae]), known as Lucky bamboo, from southern China, an area endemic for this mosquito species and for arboviruses transmitted by this vector. Here we report the results of a 1-year survey of the distribution and vector status of Ae. albopictus in Lucky bamboo nurseries in the Netherlands (July 2006–June 2007). As it had been established previously that the presence of this species was linked to the import of Lucky bamboo, the survey was conducted only on sites owned by relevant import companies. In total, 569 adult Ae. albopictus were collected with mosquito traps from 15 of the 17 (88%) glasshouses used by Lucky bamboo importers, none of which were found to be infected with dengue virus. On two occasions there was evidence that Ae. albopictus had escaped from the glasshouses, but, overall, there was no evidence that a population had become established in the greenhouses or elsewhere.