A map of the distal region of the long arm of human chromosome 21 constructed by radiation hybrid mapping and pulsed-field gel electrophoresis

We have used radiation hybrid (RH) mapping and pulsed-field gel electrophoresis (PFGE) to determine the order and positions of 28 DNA markers from the distal region of the long arm of human chromosome 21. The maps generated by these two methods are in good agreement. This study, combined with that of D. R. Cox et al. (1990, Science 250:245-250), results in an RH map that covers the long arm of chromosome 21 (21q). We have used a subtelomeric probe to show that our map includes the telomere and have identified single-copy genes and markers within 200 kbp of the telomere. Comparison of the physical and RH maps with genetic linkage maps shows "hot spots" of meiotic recombination in the distal region, one of which is close to the telomere, in agreement with previous cytogenetic observations of increased recombination frequency near telomeres.     

Kinetics of histone methylation in vivo and its relation to the cell cycle in Ehrlich ascites tumor cells.

The appearance of methylated lysines in newly synthesized histones from Ehrlich ascites tumor cells was measured during one generation time. Newly synthesized histones were pulse-labeled in vivo by L-[3H]lysine, and the time course of the uptake of label into monomethyl, dimethyl and trimethyllysine from gel-electrophoretically isolated histones F2a1 (H4) and F3 (H3) was followed. Methylation starts immediately after histone biosynthesis. It proceeds, however, more slowly than histone synthesis. Both the rate of methylation and the mechanism of methylation in F3 and F2a1 histones differ. F3 methylation can be described by a first-order reaction, i.e. the reaction rate depends only on the concentration of free methylation sites available. Rate constants of approximately 0.21 h-1 were found for all three methylation steps. Methylation in the F2a1 histone proceeds more slowly than in F3. The dimethylation step in this fraction can be described by a zero-order reaction with a rate constant which is the reciprocal of the duration of the DNA synthesis phase. Alternatively this step could be correlated with the transition of the cells from the S phase into the G2 phase. By the end of one generation time all methylation sites in all F2a1 and F3 molecules are occupied by methyl groups at a ratio of about 1:3:1 for monomethyl, dimethyl and trimethyllysine in the F3 histone. In the F2a1 molecule the methyllysines consist mainly of dimethyllysine.     

C4-dicarboxylate transport in Bacillus subtilis studied with 3-fluoro-L-erythro-malate as a substrate

Bacillus subtilis cells grown in yeast extract medium accumulated 3-fluoro-l-erythro-[1,2-(14)C(2)]malate more than 30-fold from the surrounding medium. No metabolic products derived from 3-fluoro-l-erythro-malate could be detected in these cells. l-Malate competitively inhibited transport of 3-fluoro-l-erythro-malate. This malate analogue was itself a competitive inhibitor of l-malate uptake. Cells that had been grown in yeast extract supplemented with 5 mM l-malate showed a 10-fold increased affinity towards 3-fluoro-l-erythro-malate relative to cells grown in yeast extract medium with no added malate. Our results suggest that two transport systems for l-malate can be induced in B. subtilis. The first of these systems seems to effect uptake of C(4)-dicarboxylates (l-malate, succinate, and fumarate) in yeast extract medium. The second transport system (or possibly a modification of the first transport system) seems to be induced by addition of l-malate to this medium and is also functioning in malate minimal medium.     

Attraction of male gypsy and nun moths to disparlure and some of its chemical analogues

Summary The attractive power of disparlure—the sex attractant of the gypsy moth (Lymantria/Porthetria dispar)—vs. four synthetic analogous epoxides was tested in 1972 in a pine forest near Heidelberg. With two levels of concentration in the traps (2 and 20 g), a total of 1112 nun moths (Lymantria/Porthetria monacha) and 257 gypsy moths were caught in 9 experiments. Approximately equal percentages of the two species were caught with a given compound. Disparlure was by far the most effective attractant. The other substances were between three and twenty times less effective. These experiments support the assumption that disparlure is also at least part of the sexual attractant of the nun moth. In two additional experiments, moth captures by a series of increasing disparlure concentrations (2–100 g/trap) were determined. The catches of both species increased nonlinearly with the bait concentration. The experiments are discussed with respect to new (unpublished) electrophysiological recordings from disparlure receptor cells in both species. Special attention is given to the supposed masking effect of the disparlure precursor (an olefin). This substance is ineffective as an attractant, but has been reported to reduce the attraction of gypsy moth males to disparlure or to live females. However, the olefin elicits excitatory reactions in the same type of receptor cell that responds to disparlure and the related epoxides. Furthermore, no masking of the electrophysiological response was observed with the receptor cells when the olefin was added to disparlure.Supported by the Deutsche Forschungsgemeinschaft.     

Diurnaler Säurerhythmus bei Tillandsia usneoides: Untersuchungen über den Weg des Kohlenstoffs sowie die Abhängigkeit des CO2-Gaswechsels von Lichtintensität,Temperatur und Wassergehalt der Pflanze

Summary Tillandsia usneoides, in the common sense a non-succulent plant, exhibits CO₂ exchange characterized by net CO₂ dark fixation during the night and depression of CO₂ exchange during the day. Malate has been demonstrated to accumulate during CO₂ dark fixation and to be converted to carbohydrates in light. Thus, T. usneoides exhibits CAM like typical succulents.Net CO₂ uptake during the day is increased with net CO₂ output being suppressed in duration of time and extent when light intensity increases. Furthermore, a slight increase in CO₂ fixation during the following night can be observed if the plants were treated with high light intensity during the previous day.Curves of CO₂ exchange typical for CAM are obtained if T. usneoides is kept at 15°C and 20°C. Lower temperature tend to increase CO₂ uptake during the day and to inhibit CO₂ dark fixation. Temperatures higher than 20°C favour loss of CO₂ by respiration, which becomes apparent during the whole day and night at 30°C and higher temperatures. Thus, T. usneoides gains carbon only at temperatures well below 25°C.Net CO₂ uptake during the day occurs only in moist plant material and is inhibited in plants cept under water stress conditions. However, CO₂ uptake during the night is clearly favoured if the plants dry out. Therefore dry plants gain more carbon than moist ones.Curves of CO₂ exchange typical for CAM were also obtained with 13 other species of the genus Tillandsia.The exhibition of CAM by the non-succulent T. usneoides calls for a new definition of the term succulence if it is to remain useful in characterizing this metabolic pathway. Because CO₂-fixing cells of T. usneoides possess relatively large vacuoles and are relatively poor in chloroplasts, they resembles the assimilatory cells of typical CAM-exhibiting succulents. Therefore, if succulence only means the capacity of big vacuoles to store malate, the assimilatory cells in T. usneoides are succulent. It seems to be useful to investigate parameters which would allow a definition of the term succulence on the level of the cell rather than on the level of the whole plant or plant organs.     

An Analysis of Phytochrome-mediated Anthocyanin Synthesis

Phytochrome (far red form) alone can mediate anthocyanin synthesis in the mustard seedling (Sinapis alba L.). Complete photoreversibility and reciprocity, for both red and far red light exposures over a period of at least 5 minutes, demonstrate this phytochrome involvement.     

Karyotypes,nucleoli, and amphiplasty in hybrids between Hordeum vulgare L. and H. bulbosum L.

Chromosome measurements were carried out in Hordeum vulgare, H. bulbosum, and their diploid, triploid, and tetraploid hybrids. The chromosomes were classified by using relative values, and thus karyotypes were established. For comparison of these karyotypes both relative and absolute values were used. It was concluded that differential amphiplasty occurred, whereas neutral amphiplasty could not be demonstrated. In the hybrids the relative length of the parts of the chromosomes (long arm, short arm, satellite) was not changed in comparison with these lengths in the pure species. The karyotypes of both species had considerable similarities. From comparing the mean absolute genome lengths, it was, however, concluded that in the pure species, as well as in all hybrid types, the chromosomes of H. vulgare were longer than those of H. bulbosum. In the diploid and tetraploid hybrids the mean genome lengths were shorter than those in the pure species and the triploid hybrids. The differential amphiplasty was such that the secondary constriction of chromosome 6 of H. bulbosum, did not show up in the hybrids. This could be related to the suppression of nucleolar formation in the genome of H. bulbosum, because the maximum number of nucleoli in root tip cells equalled the number of satellite chromosomes. Finally it was found that the pattern of nucleolar fusion in diploid and triploid hybrids deviated from the expectation. The results were discussed in relation to chromosomal disturbances that occurred in the hybrid tissues and that resulted in elimination of chromosomes and other effects.     

Trisomy 19 q.

Two sibs with trisomy for the long arm of chromosome 19 are reported. The common features included flat facial profile with microcephaly, hypertelorism, ptosis, prominence of the glabella, small nose with anteverted nostrils and a characteristic fish-shaped mouth. In addition congenital heart disease, physical retardation and seizures were seen in both sibs. That tristomy 19q can be suspected clinically is emphasized.     

Limitations due to water stress on leaf net photosynthesis of Quercus coccifera in the Portuguese evergreen scrub

Summary Gas exchange characteristics in leaves of the sclerophyll shrub Quercus coccifera were studied in the natural habitat in Portugal during spring and during the summer dry period. Compared to other sclerophyll species growing at the same site, photosynthesis in leaves of Quercus coccifera was less affected by water stress. Moderate water stress after six weeks of drought led to large decreases in stomatal conductance but no change in mesophyll photosynthetic capacity as compared to late spring. Leaf internal CO₂ pressure remained near 220 bar during diurnal courses in the spring. On midsummer days, leaf internal CO₂ decreased from a late morning value of 200 bar to a late afternoon value of approximately 150 bar. In contrast to Quercus suber (Tenhunen et al. 1984), restriction of CO₂ supply due to stomatal closure reduced net CO₂ uptake at midday and in the afternoon during midsummer. A decrease in leaf carboxylation efficiency and an increase in CO₂ compensation point at midday also played an important role in determining the diurnal course of net photosynthesis. During the late stages of drought in September, severe water stress led to reduction in mesophyll photosynthetic capacity and further reduction in leaf conductance. The observed decrease in mesophyll photosynthetic capacity was correlated with decrease in the daily minimum leaf water potential to greater negative values than-30 bar. At this time, CO₂ saturated photosynthetic rates decreased as much as 50% over the course of a day when measured at constant saturating light, 32° C leaf temperature, and a water vapor mole fraction difference between leaf and air of 30 mbar bar^-1.