Developmental changes in high-affinity uptake of GABA by cultured neurons

High-affinity uptake of [³H]-aminobutyric acid (GABA) was studied in cultures of neonatal rat cortical neurons grown on pre-formed monolayers of non-neuronal (glial) cells. Both the maximum rate (V _max) and, to a smaller extent, theK _m of [³H]GABA uptake increased with time. In addition, in parallel with these changes, 2,4-diaminobutyric acid and cis-3-aminocyclohexane-1-carboxylic acid (ACHC), compounds which are considered typical substrate/inhibitors of GABA uptake in neurons, became progressively stronger inhibitors of [³H]GABA uptake. Consequently, the present results may mean that the studies using uptake, of [³H]GABA, [³H]ACHC, or [³H]DABA as a specific marker for GABAergic neurons differentiating during the ontogenetic development of the central nervous system may have to be interpreted with caution.     

Plastid transformation in greening scales of the onion bulb (Allium cepa,Alliaceae)

The greening of the upper part of the outerAllium cepa L. bulb scales, in particular along the vascular regions, is limited to the hypodermal cells in which typical leucoplasts are transformed to normal and functional chloroplasts. This process is light dependent and cannot afterwards be reversed or modified by darkness. The changes in fine structure are described and briefly discussed.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday and 55 years after the publication of his Grundriß der Cytologie.     

Site-specific aflatoxin B1 adduction of sequence-positioned nucleosome core particles

The question of how the presence of nucleosomal packing of DNA modifies carcinogen interaction at specific sites cannot be answered by studies on whole chromatin or bulk nucleosomes because of the heterogeneity of DNA sequences in the particles. We have circumvented this problem by using nucleosomes that are homogenous in DNA sequence and hence in DNA-histone contact points. A cloned DNA fragment containing a sea urchin 5 S gene which precisely positions a histone octamer was employed. By using 32P end-labeled DNA and genotoxins that allow cleavage at sites of attack, the frequency of adduction at every susceptible nucleotide can be determined on sequencing gels. The small methylating agent dimethyl sulfate and the bulky alkylating agent aflatoxin B1-dichloride (AFB1-Cl2) were used to probe the influence of DNA-histone interactions on DNA alkylation patterns in the sequence-positioned core particle. We find dimethyl sulfate to bind with equal preference to naked or nucleosomal DNA. In contrast, AFB1-Cl2 binding is suppressed an average of 2.4-fold at guanyl sites within nucleosomes compared with AFB1-Cl2 affinity at the corresponding site in naked DNA. The DNA is more accessible in regions near the particle boundary. We observe no other histone-imposed localized changes in AFB1-Cl2 sequence specificity. Further, sites of DNase I cleavage or proposed DNA bending show neither enhanced nor reduced AFB1-Cl2 adduction to N7-guanine. Since AFB1-Cl2 binding sites lie in the major groove, nucleosomal DNA appears accessible to AFB1-Cl2 at all points of analysis but with an access which is uniformly restricted in the central 100 nucleotides of the core particle. The data available do not indicate further localized or site-specific perturbations in DNA interactions with the two carcinogens studied.     

Consequences of herbivory in the mountain birch (Betula pubescens ssp tortuosa): importance of the functional organization of the tree

Summary Three types of experiments indicate that the functional organization of the mountain birch may influence the ways in which the tree responds to simulated or natural herbivory. The first experiment showed that herbivory to both short and long shoot leaves affects plant development but, because growth largely proceeds by resources of the previous year, is manifested only in the year following the damage. The second experiment showed that even partial damage to a single long shoot leaf caused the axillary bud of that leaf to produce a shorter shoot the next year. Therefore, the value of a leaf depends also on the organ which it is subtending. In the third experiment we manipulated the apical dominance of shoots in ramets and caused improvement to leaf quality in extant shoots. Ramets within a tree responded individually, probably mediated by disturbance of the hormonal control because removal of apical buds elicited the response although removal of the same number of basal buds did not. Induced amelioration is a different response to induced resistance. The two responses are triggered by different cues and may occur in the same plant. By altering hormonal balance of shoots it is potentially possible for herbivores to induce amelioration of food quality. The ways in which herbivory is simulated may explain variability of results obtained when herbivory-induced responses in plants have been studied.     

Salt-soluble lectins of corn grain

Lectins extracted from corn (Zea mays L.) kernel with Tris-HCl buffer pH 7.5 were isolated from the crude extract by affinity chromatography on Sepharose 6B-N-acetyl-d-galactosamine and Sepharose 6B-methylα-d-mannoside, and also by lectin affinity chromatography using concanavalin A and Lens culinaris lectin as ligands. According to preferential monosaccharide specificity, salt-soluble lectins of corn seed comprise at least two distinct types: N-acetyl-d-galactosamine-interactive and mannose-interactive lectins. The extracted lectins are unstable, with a tendency to form aggregates during storage.     

Mapping in the mouse of the region homologous to the rat growth and reproduction complex (grc)

Offprint requests: J. Klein.     

Different temperature profiles of enzyme secretion by two common strains ofTrichoderma reesei

Summary We have investigated the effects of high and low temperature on the synthesis and secretion of cellulases and other enzymes by two common and readily available strains ofTrichoderma reesei. While some effects were similar in both strains QM9414 and RUT-C30 (a reduction in cellulase production but stimulation of xylanase production at high temperature, and alterations in expression of the cellulase complex at low temperature), some specific differences between the strains were determined, most significantly an enhanced specific secretion rate (secretion/growth) at low growth temperature for QM9414.     

Determination of trace elements in standard reference materials by the ko-standardization method

Biological Trace Element Research - The ko-standardization method is suitable for routine multielement determinations by reactor neutron activation analysis (NAA). Investigation of NIST standard...     

Respiratory Rate as a Regulatory Factor in the Biosynthesis of the Denitrification Pathway of the Bacterium Paracoccus denitrificans

The decrease in the electron flow of the aerobic respiratory chain of the bacterium Paracoccus denitrificans, owing to either the drop in the saturation of terminal oxidases by oxygen or to the inhibition of the rate of respiration by azide or nitrite, resulted in the synthesis of dissimilatory nitrate reductase and nitrite reductase. The dependence of the resulting activities of the two enzymes (after a three-hour adaptation) on the initial value of the parameter V_max/k_La (oxidase activity of the volume unit of the culture divided by the volumetric oxygen transfer coefficient) or on the concentrations of the inhibitors had a similar form, characterized by the appearance of a maximum. The increasing parts of the obtained curves reflect the synthesis of enzymes, probably initiated by the increase in the intracellular degree of reduction, the subsequent drop being evidently in connection with the lack of metabolic energy for biosynthesis. The possible mechanisms of the effect of nitrogenous terminal acceptors (NO^-₃ and NO^-₂) on the formation of the denitrification pathway are discussed.