Initial decomposition ofNymphoides peltata (Gmel.) O. Kuntze (Menyanthaceae), as studied by the leaf-marking method

Summary In this paper the leaf-marking method as used for the study of the development and initial decomposition of floating leaves is described and the reliability of the various measurements is tested and/or discussed. Some general results obtained withNymphoides peltata (Gmel.) O. Kuntze in tanks and in the field are presented and crltically discussed. Autolysis followed by microbial decay was in all cases the most important factor by which leaves disintegrated. In the field plots animals were responsible for the disappearance of 22% of the total leaf area produced during a growth season. This is, however, the combined effect of consumption and damage succeeded by microbial decay. Real grazing can be estimated to be no more than 10% of the production of floating leaves. Fungi can have an important role in initial decomposition, especially after the flowering period, as is demonstrated forSeptoria villarsiae Desm. All damage types show temporal and, in the case of animals, also spatial distribution patterns.     

Transport of amino acids and ammonium in mycelium of Agaricus bisporus.

Mycelium of Agaricus bisporus took up methylamine (MA), glutamate, glutamine and arginine by high-affinity transport systems following Michaelis-Menten kinetics. The activities of these systems were influenced by the nitrogen source used for mycelial growth. Moreover, MA, glutamate and glutamine uptakes were derepressed by nitrogen starvation, whereas arginine uptake was repressed. The two ammonium-specific transport systems with different affinities and capacities were inhibited by NH(+)(4), with a K(i) of 3.7 microM for the high-velocity system. The K(m) values for glutamate, glutamine and arginine transport were 124, 151 and 32 microM, respectively. Inhibition of arginine uptake by lysine and histidine showed that they are competitive inhibitors. MA, glutamate and glutamine uptake was inversely proportional to the intracellular NH(+)(4) concentration. Moreover, increase of the intracellular NH(+)(4) level caused by PPT (DL-phosphinotricin) resulted in an immediate cessation of MA, glutamine and glutamate uptake. It seems that the intracellular NH(+)(4) concentration regulates its own influx by feedback-inhibition of the uptake system and probably also its efflux which becomes apparent when mycelium is grown on protein. Addition of extracellular NH(+)(4) did not inhibit glutamine uptake, suggesting that NH(+)(4) and glutamine are equally preferred nitrogen sources. The physiological importance of these uptake systems for the utilization of nitrogen compounds by A. bisporus is discussed.     

Seasonal variation in food allergy to apple

The aim of the study was to investigate the possibility of a seasonal variation in reactivity to apples in 27 birch pollen allergic patients. Before and during the birch pollen season 1998, the patients were subjected to double-blind, placebo-controlled food challenges (DBPCFCs) with grated fresh Golden Delicious apple followed by an open food challenge with whole fresh apple. The clinical reactions elicited during the challenges were evaluated both by the patients and the investigators. Moreover, the skin reactivity and the in vitro reactivity to apple were evaluated by skin prick test (SPT), leukocyte histamine release (HR), measurement of specific IgE, and immunoblotting experiments. The sensitivity of the DBPCFC, when compared with the result of the open challenge, was 0.74 (14/19) before the season and 0.80 (16/20) during the season. None of the patients reacted to the blinded challenge without a subsequent reaction to the open challenge. One placebo reaction was registered both before and in season, but not in the same patient. The patient scores of the first positive challenges, and the maximal scores of each combined blinded and open challenge session, were significantly increased during the pollen season (P<0.05). The scores of the open challenge were significantly higher than the scores of the DBPCFC both before the season and during the in-season challenges (P<0.05). Specific IgE against Golden Delicious increased during season (P<0.05), while neither SPT, HR, nor immunoblotting experiments could confirm an increase in reactivity. In conclusion, the results of the oral challenge tests indicated an increase in clinical reactivity to apples during the birch pollen season in birch pollen allergic individuals.     

Prey-capture techniques and prey preferences of Corythalia canosa and Pystira orbiculata, ant-eating jumping spiders (Araneae, Salticidae)

Corythalia canosa from Florida is an unusual salticid because it is known to eat ants. This species' specialized behaviour for catching ants is described in detail for the first time and compared to its behaviour for catching other insects. Pystira orbiculata from Queensland is shown to be another ant-eating salticid, although its behaviour for catching ants seems less specialized than that of C. canosa. Three different types of tests of prey preference were carried out. In each type of test C. canosa and P. orbiculata took ants in preference to other insects. Another species of salticid, Trite planiceps from New Zealand, failed to eat ants in these tests, although T. planiceps often attacked then released the ants. Corythalia canosa's and P. orbiculata's preference for ants, and their prey-specific predatory behaviour for catching ants, are shown not to depend on prior experience with ants.     

X-ray absorption spectroscopy of selenium-containing amino acids

Received: 2 April 1999 / Accepted: 17 September 1999     

Disruption of energy metabolism and smoltification during exposure of juvenile atlantic salmon (Salmo salar) to low pH

Juvenile Atlantic salmon were held for 76 days at pH 4.7 during the period when the final stages of smoltification normally occur. Control salmon (pH 6.5) had significant increases in weight, length and liver somatic index which were not observed in those held at low pH. Condition factor decreased in both groups but to a significantly greater extent in the low pH group. After 15 days levels of ADP and glucose were higher and AEC, CP and glycogen were lower in muscles of salmon exposed to low pH. These qualitative differences were maintained until the end of the experiment. ATP and total adenylate concentrations in muscle were lower after 62 days of exposure to low pH compared to controls. The levels of ATP, total adenylates, AEC and glucose were consistently higher in livers of salmon exposed to low pH than those of controls. There were no differences in liver concentrations of AMP, CP and glycogen between the two treatments or with time of exposure within each treatment. The results suggest that exposure of juvenile Atlantic salmon to low pH increased gluconeogenesis and decreased food intake to the detriment of growth.