Induction of transverse polarity by blue light: An all-or-none response

Phototropic stimulation induces a spatial memory. This was inferred from experiments with maize (Zea mays L.) coleoptiles involving opposing blue-light pulses, separated by variable time intervals, and rotation on a horizontal clinostat (Nick and Schafer, 1988b, Planta 175, 380-388). In those experiments, individual seedlings either curved towards the first or towards the second pulse, or they remained straight. Bending, if it occurred, seemed to be an all-or-none response. Intermediates, i.e. plants, bending only weakly, were not observed. In the first part of the present study it was attempted to create such intermediates. For this purpose the strength of the first, inducing, and the second, opposing, pulse was varied. The result was complex: (i) Individual seedlings maintained the all-or-none expression of spatial memory. (ii) However, on the level of the whole population, the time intervals at which a given response type dominated depended on the fluence ratio. (iii) Furthermore, the final curvature was determined by the fluence ratio. These results are discussed in terms of a blue-light-induced transverse polarity. This polarity initiates from a labile precursor, which can be reoriented by an opposing stimulation (indicated by the strong bending towards the second pulse). The strong curvatures towards the first pulse over long time intervals reveal that, eventually, the blue-light-induced transverse polarity becomes stabilised and thus immune to the counterpulse. In the second part of the study, the relation between phototropic transduction and transverse polarity was characterised by a phenomenological approach involving the following points: (i) Sensory adaptation for induction of transverse polarity disappears with a time course similar to that for phototropic sensory adaptatation. (ii) The fluence response for induction of transverse polarity is a saturation curve and not bell-shaped like the curve for phototropism (iii) For strong counterpulses and long time intervals the clinostat-elicited nastic response (Nick and Schafer 1989, Planta 179, 123-131) becomes manifest and causes an "aiming error" towards the caryopsis. (iv) Temperature-sensitivity of polarity induction was high in the first 20 min after induction, then dropped sharply and rose again with the approach of polarity fixation. (v) Stimulus-summation experiments indicated that, for different inducing fluences, the actual fixation of polarity happened at about 2 h after induction. These experiments point towards an early separation of the transduction chains mediating phototropism and transverse polarity, possibly before phototrophic asymmetry is formed.     

Environmental factors affecting the life-tables ofTetranychus urticae (Acari: Tetranychidae) III. Host-plant nutrition

First, the literature of the last two decades on nutritional effects of host plants on spider mites is briefly reviewed. Second, experiments are described that subjected micro-propagated apple trees to four different levels of each macronutrient N, P and K. Spider mites (Tetranychus urticae Koch) feeding on leaf disks of these plants were checked for their developmental time, egg production and longevity. Plant analysis revealed that the concentration of N, P and K corresponded to the respective treatments. The content of phenolic compounds in the leaves increased with N and P deficiency. In the N experiment, spider-mite preimaginal developmental rate and oviposition rate were both positively correlated with leaf N. Often, fecundity was positively correlated with N and carbohydrate content of the leaves, and negatively with the phenolic content. Longevity of the two-spotted spider mite was not significantly affected by any treatment. The K experiments yielded only minor differences in plant contents as well as in spider-mite biology.From these mite data, file-tables were constructed and statistically analyzed by the Jackknife technique. The life-table analysis showed a gradual decline in the intrinsic rate of natural increase (r _m) with N and P deficiency. With all experiments pooled,r _m was clearly correlated to leaf N and particularly to the content of phenolic compounds in the leaves. Nitrogen shortage had the most distinct influence on mite population growth: in a range of 1.5–3.0% leaf N,r _m increased by a factor of 4, the number of multiplications per generation (R ₀) by 11, and the doubling time of the population was prolonged 4-fold on severely N deficient leaves.     

Mediated amperometric determination of xylose and glucose with an immobilized aldose dehydrogenase electrode.

An enzyme electrode was constructed for amperometric determination of xylose and glucose. The electrode is based on the PQQ-dependent membrane-bound aldose dehydrogenase (ALDH) from Gluconobacter oxydans. ALDH was covalently immobilized on a graphite electrode. Immobilized dimethylferrocene, soluble ferrocene carboxylic acid and phenazine methosulphate were used as electron transfer mediators. When xylose was measured electrochemically using an electrode modified with ALDH and dimethylferrocene, the linear measurement range extended to 100 mM. For glucose measurement the linear measurement range was about one-tenth of that for xylose. The electrode showed fairly good stability; 50% of the original electrode response was still obtained after 5 days of intermittent use. The effect of possible leakage of adsorbed mediator was determined by measuring the response of an electrode with soluble mediator as a function of time. The reproducibility of the electrode was good, the standard deviation of the electrode response in ten measurements with the same electrode being only 2.7%.     

Investigations on possible genotoxic effects ofFusarium toxins in boars

For several weeks, boars were fed feedstuff containing mycotoxins (zearalenone, nivalenol, and deoxynivalenol). To determine a possible mutagenic effect of this feedstuff, the boars were examinated for structural chromosome aberrations in the lymphocytes. The investigations indicate a genotoxic effect on the boars’ lymphocytes.     

Responses of the photosynthetic flagellate,Euglena gracilis,to hypergravity

Motility and orientation has been studied in the unicellular photosynthetic flagellate, Euglena gracilis, using real time image analysis capable of tracking up to 200 cells simultaneously in the slow rotating centrifuge microscope (NIZEMI) which allows one to observe the cells' swimming behavior during centrifugation accelerations between 1 g and 5 g. At 1 g the cells show a weak negative gravitaxis, which increases significantly at higher accelerations up to about 3 g. Though most cells were capable of swimming even against an acceleration of 4.5 g, the degree of gravitaxis decreased and some of the cells were passively moved downward by the acceleration force; this is true for most cells at 5 g. The velocity of cells swimming against 1 g is about 10% lower than that of cells swimming in other directions. The velocity decreases even more drastically in cells swimming against higher acceleration forces than those at 1 g. The degree of gravitactic orientation drastically decreases after short exposure to artificial UV radiation which indicates that gravitaxis may be due to an active physiological perception rather than a physical effect such as an asymmetry of the center of gravity within the cell. Offprint requests to: D.-P. Häder     

Lactic acid excretion via carrier-mediated facilitated diffusion in Lactobacillus helveticus

Summary During growth on a complex medium containing 2% (w/v) lactose, Lactobacillus helveticus produced about 180 mm lactate. Due to the acidification, the external pH decreased to 3.7. The pH remained constant at a level of 0.5–0.7 units (40 mV), and µ_Lac decreased gradually from –60 to 0 mV. The mechanism of lactate extrusion was studied with resting cells. Upon dilution of lactate-loaded cells in a buffer containing [¹⁴C]-lactate, a typical counterflow was observed, suggesting that a carrier system was employed in lactate excretion. Influx of lactate could not be driven by an artificial membrane potential, indicating that lactate was electroneutrally transported. By examining efflux under various lactate anion and lactic acid concentrations, the undissociated form of the acid was shown to influence the velocity of the transport process. A pH-dependent apparent K _m value of the carrier system was observed in efflux experiments with increasing internal lactate concentrations. It was concluded that the mode of end-product excretion can be defined as a carrier-mediated facilitated diffusion with the undissociated lactic acid or the lactate anion in symport with one proton, respectively, as the object of transport.Abbreviations L _tota total lactate - L _undissb free lactic acid - L _dissc lactate anion - pH_ed external pH - pH_ie internal pH - pH transmembrane H⁺ gradient - µ_Lacf transmembrane gradient of total lactate - µ_HLg transmembrane gradient of the free lactic acid - µ_Lh transmembrane gradient of the lactate anion - V _Effii efflux velocity Offprint requests to: G. Gottschalk     

Penicillium verrucosum in feed of ochratoxin A positive swine herds

Ochratoxin A contamination of cereal feed grain was monitored during October 1989–September 1990 by analysis of blood samples from slaughter swine in Sweden. The detection of ochratoxin A in swine blood was used as a method to identify swine herds fed ochratoxin A contaminated feed. The contamination level of ochratoxin A in the blood of the positive herds was in the range 2–45 ng/ml with the mean concentration 5.2 ng/ml. Feed samples for mycological analysis were collected from both ochratoxin A positive herds (2 ng/ml blood) and ochratoxin A negative herds (<2 ng/ml blood). From the ochratoxin A positive herds and the ochratoxin A negative herds 22 and 21 feed samples were collected, respectively. No quantitative differences in mould content, as determined by colony forming units, were observed between the two groups. However, there were differences in the mycoflora. The incidence of storage fungi (Penicillium and Aspergillus spp.) was significantly higher (p < 0.05) in feed from ochratoxin A positive herds. Particularly, Penicillium verrucosum was found to be significantly more common (p < 0.001). Altogether 274 isolates were screened for their ability to produce ochratoxin A. Ochratoxin A producers were found only within P. verrucosum; 38% of the 63 isolates produced detectable amounts of ochratoxin A. Ochratoxin A producing isolates of P. verrucosum were found in 60% of the feed samples collected from ochratoxin A positive swine herds and in one sample (5% ) of the feed samples collected from the ochratoxin A negative herds.     

Polymorphic restriction sites of type II collagen gene: their location and frequencies in the Finnish population

Restriction fragment length polymorphism (RFLP) of the cartilage-specific type II collagen gene has been studied in the Finnish population. Two high-frequency alleles, also reported in other populations, were detected. The HindIII allele had a frequency of 0.33, and that detected with PvuII a frequency of 0.46. Both of these frequencies resembled the ones reported for other populations. Also one BamHI allele, not earlier reported, was found at a low frequency. Two other previously reported polymorphisms for BamHI and EcoRI were not detected in the Finnish population. The RFLPs showed a fair agreement with the Hardy-Weinberg equilibrium. A linkage disequilibrium was found between PvuII and HindIII markers. The alpha 1(II) collagen gene seems to be more conserved in populations of various origins than the alpha 2(I) collagen gene. These polymorphic collagen markers would be useful in linkage studies of various inherited cartilage disorders.