Monitoring watercourse vegetation, a synecological approach to dynamic gradients

Changes in vegetation under reduced control measures over 3 to 5 years in watercourses in a rural environment in The Netherlands were evaluated. A method to deal with slow changes on a steep gradient is presented. The gradient with various vegetation types between the middle of the watercourse and the bank-top was split up into zones. Species composition of each zone was evaluated using literature on syntaxonomy. Cover of character species, multiplied by the width of the zones, was used to quantify the contribution of various syntaxa in the vegetation. Changes in these contribution data were used to evaluate changes over the years. The method was applied to two experiments in which cleaning frequency was reduced. Submerged vegetation of Callitriche-Ranunculetum penicillati in one and of Potamogetonetalia pectinati in the other case, hardly changed. Emergent vegetation of Nasturtio-Glycerietalia or Sparganio-Glycerietum fluitans tended to expand into the submerged zone. Bank vegetation began to show signs of development into ruderal vegetation, as a shift from Molinio-Arrhenatheretea into Artemisietea was detected. The method allowed the conclusion that conditions were too eutrophic in both experiments for a diverse brook vegetation development without additional habitat improvement.     

Priming relieves dormancy in lettuce seeds independently of changes in osmotic constituents

The relationship was studied between germination and dormancy of lettuce seeds ( Lactuca sativa L. cv. Musette) and both soluble amino nitrogen metabolism and osmotic potential. Germination at 15°C in darkness coincided with a rise in the levels of free amino acids and total soluble amino nitrogen compounds and in the activity of glutamine synthetase (GS, EC nr. 6.3.1.2). In further experiments GS activity was used as indicator of soluble amino nitrogen metabolism. GS activity increased after the start of growth indicated by an increasing intolerance to desiccation. At 30°C seeds did not germinate, unless dormancy was broken beforehand during incubation at 2° or 15°C (priming). The alleviation of dormancy occurred much earlier than the rise in the activity of GS. Priming at 15°C in polyethylene glycol instead of water retarded the breaking of dormancy and at –1.28 MPa even stimulated the induction of secondary dormancy, but did not prevent a continued rise in the activity of GS. GS activity was also not reduced during induction of secondary dormancy by dehydration of primed seeds, which antagonized the beneficial effect of priming. Psychrometric measurements showed that osmotic potential (Ψ_π) of the seeds remained constant during prolonged priming in polyethylene glycol at 15°C. During incubation in water, Ψ_π increased both prior to and after the moment of germination to less negative values. It is concluded that changes in the level of dormancy in lettuce seeds occur independently of soluble amino nitrogen metabolism and of changes in Ψ_π.     

The Synthesis and Antiherpetic Activity of DHBG and Some Analogs

Abstract

Several acyclic guanosine analogs have been synthesized and tested for antiviral activity.     

Succession dynamics of aquatic lake vegetation after restoration measures: increased stability after 6 years of development

For 7 years, development of submerged vegetation was monitored after fish stock removal during the final phase of a restoration program in the shallow, 2.1 km² Lake Loenderveen (The Netherlands). The lake shifted from a turbid, phytoplankton-dominated state, to a clear, macrophyte-dominated state. Vegetation development was very dynamic during years 1–5. Dominance of Elodea nuttallii (Planchon) St. John and Najas marina L. alternated in the initial few years and separate development of Chara species was recorded locally. Elodea nuttallii achieved the highest coverage in the 5th year, but part of the vegetation collapsed in the 6th year. In year 7, the system had recovered and became more stable. The dynamic developments, and spatial differences, are possibly explained by waterfowl interactions, soil nutrient status, and differences in growth form strategies of the species. It was concluded that the trophic level of the lake water was low enough for lake vegetation to recover following removal of most of the fish stock, but stability of the clear water state has increased considerably only after 6 years of development.     

Cascade of neural events leading from error commission to subsequent awareness revealed using EEG source imaging

The goal of the present study was to shed light on the respective contributions of three important action monitoring brain regions (i.e. cingulate cortex, insula, and orbitofrontal cortex) during the conscious detection of response errors. To this end, fourteen healthy adults performed a speeded Go/Nogo task comprising Nogo trials of varying levels of difficulty, designed to elicit aware and unaware errors. Error awareness was indicated by participants with a second key press after the target key press. Meanwhile, electromyogram (EMG) from the response hand was recorded in addition to high-density scalp electroencephalogram (EEG). In the EMG-locked grand averages, aware errors clearly elicited an error-related negativity (ERN) reflecting error detection, and a later error positivity (Pe) reflecting conscious error awareness. However, no Pe was recorded after unaware errors or hits. These results are in line with previous studies suggesting that error awareness is associated with generation of the Pe. Source localisation results confirmed that the posterior cingulate motor area was the main generator of the ERN. However, inverse solution results also point to the involvement of the left posterior insula during the time interval of the Pe, and hence error awareness. Moreover, consecutive to this insular activity, the right orbitofrontal cortex (OFC) was activated in response to aware and unaware errors but not in response to hits, consistent with the implication of this area in the evaluation of the value of an error. These results reveal a precise sequence of activations in these three non-overlapping brain regions following error commission, enabling a progressive differentiation between aware and unaware errors as a function of time elapsed, thanks to the involvement first of interoceptive or proprioceptive processes (left insula), later leading to the detection of a breach in the prepotent response mode (right OFC).     

Deoxyglucose inhibition of protein glycosylation: Effects of nucleotide deoxysugars on the formation of glucosylated lipid intermediates

The UDP-derivative of deoxyglucose (UDP-deoxyglucose) inhibits the formation of dolichyl monophosphate glucose (Dol-P-glucose) in chick embryo cell membranes but has no effect on Dol-PP di-N-acetylchitobiose [Dol-PP-(GlcNAc)₂]formation. The effects of UDP-deoxyglucose are not reversed by Dol-P, nor is Dol-P-deoxyglucose formed from this derivative. GDP-deoxyglucose inhibits formation of both Dol-P-glucose and Dol-PP-(GlcNAc)₂. It is shown that GDP-deoxyglucose inhibits in these cases by competition with physiological nucleotide sugars for Dol-P. GDP-deoxyglucose and UDP-deoxyglucose also prevent the attachment of the peripheral glucose residues in Dol-PP-(GlcNAc)₂-Mans_yGlc₃, the immediate precursor of protein-bound oligosaccharides. The inhibition by GDP-deoxyglucose is only in part reversed by Dol-P, probably because deoxyglucose is incorporated into the lipid-linked oligosaccharide instead of glucose.     

Lack of Control by Early Pistillate Ethylene of the Accelerated Wilting of Petunia hybrida Flowers

Well before pollen tube penetration, ethylene has begun to disseminate from pollinated styles of Petunia hybrida flowers. Previous stigmatic application of aminoethoxyvinylglycine (AVG) completely prevented this ethylene synthesis, indicating that the endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) in pollen is not readily converted on the stigma. Compared to other flower parts, the capacity of the ethylene forming enzyme was largest in the stigma. When applied to the stigma, ACC caused ethylene synthesis, but did not accelerate wilting, unless high concentrations (20 nanomols) were used. Upon pollination or stigma wounding, the early ethylene evolved exclusively from the gynoecium, much later followed by the synthesis of corolla ethylene. Employing wideneck Erlenmeyer flasks, the competitive inhibitor of ethylene action, norbornadiene, was applied to entire flowers in situ, with delaying effects on wound-induced wilting. In contrast, norbornadiene treatment of styles alone, using capillaries, could not postpone wilting. Pollination with foreign pollen species did not lead to accelerated corolla wilting, notwithstanding considerable synthesis of ethylene during the first 5 hours. In situ treatment of the stigma with AVG considerably delayed wound- and pollination-induced wilting. Removal of the entire AVG-treated style 6 hours after stigma wounding still allowed for the postponement of the accelerated wilting, even at very low concentrations of AVG. It is concluded that early stylar ethylene does not play a role in the acceleration of wilting but that, much later, corolla ethylene does, induced by a mobile wilting factor from the stigma, which is ACC.     

Catalytic dehydrogenation of reducing sugars in alkaline solution

Aldoses in alkaline medium under the catalytic action of platinum or rhodium are converted into aldonic acids with high selectivity and with concomitant evolution of hydrogen gas. The dehydrogenation reaction has been studied for 25 different mono- and di-saccharides, and is generally applicable for reducing sugars. The influence of several reaction variables has been studied, leading to an adsorption model in which both the negatively charged O-1 and the close contact of H-1 with the catalyst surface are considered to be driving forces for the transfer of hydride from C-1 of the sugar to the catalyst.     

An inhibitor of mannosylation of retinyl-phosphate

The guanosine disphospate and uridine diphosphate esters of the antiviral sugar analog 2-deoxy-2-fluoro-D-glucose (GDP-FGlc and UDP-FGlc) were synthesized and tested as inhibitors of formation of lipid-linked sugars in cell-free extracts . Formation of dolichol-phosphate mannose and of dolichol-diphosphate di-N-acetylchitobiose were not inhibited by either sugar nucleotide. Formation of dolichol-phosphate glucose was inhibited by UDP-FGlc, not by GDP-FGlc. Although GDP-FGlc did not inhibit formation of dollchol-phosphate mannose, it did inhibit formation of retinol-phosphate mannose from retinol-phosphate and GDP-Man. This inhibition was not reversed by exogenous retinol-phosphate, nor was FGIc from GDP-FGlc incorporated into retinolphosphate-linked derivatives. As FGLc inhibits formation of dolichol-phosphate mannose in intact cells, but does not decrease pool sizes of GDP-Man and dolichol-phosphate (Datema et al., 1980, Eur. J. Biochem.109, 331–341), we discuss that inhibition of formation of retinol-phosphate mannose by one of the metabolites of FGlc, namely GDP-FGlc, may lead to decreased synthesis of dolichol-phosphate mannose in FGlc-treated cells. This implies a role for vitamin A in the dolichol cycle of protein glycosylation.