NUCLEAR DNA CONTENT IN POPULATIONS OF PINUS RIGIDA

Five populations of Pinus rigida growing in contrasting ecological situations ranging from North Carolina (35°53'N latitude) to Quebec (45°06'N latitude) showed no significant variation in amounts of nuclear DNA with respect to germinating seedlings. Nuclear volume of dormant nuclei also showed no significant variation between and within populations, a finding that is consistent with the concept that the basic 2C DNA value of Pinus rigida is uniform under all habitats. This finding is in contrast to numerous reports for other coniferous species.     

High level of divergence of male-reproductive-tract proteins, between Drosophila melanogaster and its sibling species, D. simulans

We compared male-reproductive-tract polypeptides of Drosophila melanogaster and D. simulans by using two-dimensional gel electrophoresis. Approximately 64% of male-reproductive-tract polypeptides were identical between two randomly chosen isofemale lines from these two species, compared with 83% identity for third-instar imaginal wing-disc polypeptides. Qualitatively similar differences were found between reproductive tracts and imaginal discs when D. sechellia was compared with D. melanogaster and with D. simulans. When genic polymorphism was taken into account, approximately 10% of male- reproductive-tract polypeptides were apparently fixed for different alleles between D. melanogaster and D. simulans; this proportion is the same as that found for soluble enzymes by one-dimensional gel electrophoresis. Strikingly, approximately 20% of male-reproductive- tract polypeptides of either D. melanogaster or D. simulans had no detectable homologue in the other species. We propose that proteins of the Drosophila male reproductive tract may have diverged more extensively between species than have other types of proteins and that much of this divergence may involve large changes in levels of polypeptide expression.      

A Comparison of Internal Standards for Plant Cytophotometry

Plant cell nuclei were compared with chicken erythrocyte nuclei for use as internal standards for microspectrophotometry. The amount of DNA per nucleus and the coefficient of variation for measurement of individual nuclei were determined for cells from dormant embryos of Pinus taeda and Pinus coulteri, from onion root tips and from chicken erythrocytes. The chicken erythrocytes had the least variability and thus were best suited for use as a standard. Onion root tips were least suitable, with a coefficient of variation 2 1/2 times that of erythrocytes. Although onion root tips have been used as an internal standard in other studies, their mitotic activity, in contrast with the nonreplication of DNA of mature erythrocytes, is reflected in a broad distribution of nuclei with values in the 2C-4C range. Coulter pine mature embryos were at the 3C level, whether dry or hydrated, while loblolly pine embryos were in the 2C state. This confirms previous reports. The coefficient of variability for the pine embryo cells was 1 1/2 times that of erythrocytes for nonhydrated seeds and twice the erythrocyte value for hydrated seeds. The larger 2C values for pine (26 pg for P. taeda and 17 pg for P. coulteri) are closer to values expected for many plant species than the 3 pg level of the chicken erythrocytes. Dormant P. taeda embryo cells (2C) are suggested as an alternative where the experimental material has large DNA values and/or chicken erythrocytes are difficult to procure. Large sample size is recommended for the plant materials if they are to be used as internal standards in Feulgen cytophotometry.     

Cytophotometric differentiation of high elevation spruces: physiological and ecological implications

Red and black spruce and their hybrids can be determined by morphological indices; however, the criteria are somewhat subjective and increasingly difficult to use at higher elevations. Although the chromosome number is identical (2n = 24), red spruce has twice as much nuclear DNA (48 pg) than black spruce (24 pg) and thus the species and their hybrids can also be separated by cytophotometry. This is relevant to spruce decline studies because black spruce is much more resistant to high elevation environmental stresses, both natural and anthropogenic. It also has implications for the effect of climatic changes on the composition of high elevation spruce-fir forests because red spruce can outcompete black spruce under more mesic conditions. Four elevation transects sampling spruce on the east and west sides of Mount Washington (New Hampshire) and Camels Hump (Vermont) and a single transect on the southwest side of Whiteface Mountain (New York) were made to investigate the degree of hybridization and introgression between these two species. A positive correlation was found between increased elevation and increased black spruce genes on Mount Washington and Camels Hump. Pure black spruce was found on Mount Washington from 1356 m to 1582 m. No pure black or red spruce was found on Camels Hump although the proportion of red spruce alleles was significantly greater on Camels Hump. All trees sampled at all elevations on Whiteface Mountain were pure red spruce. Thus the proportion of black spruce alleles in high elevation spruce populations decreases from east to west. This closely parallels the increase in spruce decline which increases from east to west.     

Pre-induction priming of the uterine cervix with oral prostaglandin E2 and a placebo

A double blind study was undertaken to determine the effectiveness or oral prostaglandin E2 as a means of improving the pelvic score prior to induction of labour. 48 patients who were greater than 37 were gestation and who had Bishop scores of less than 6 entered the study. Ten tablets were given on an hourly regime. Of 25 patients in the prostaglandin group, 17 were considered successes (68.0%), whereas of 23 patients who received a placebo, 9 were successes (39.1%). No adverse effects were recorded. Prostaglandin E2 is therefore considered a safe and effective method for priming the unfavourable cervix prior to induction of labour.     

Cotrans: A Program for Cotransduction Analysis

COTRANS is a program for analyzing cotransduction data. It calculates distances from pairwise cotransduction frequencies, computes crossovers required to obtain each observed recombinant class, and applies rules to draw conclusions about order. The rules are based on the correlation between the frequency of the classes and the number of required crossovers for each possible ordering compatible with the distance calculations. The procedure emulates a geneticist's stepwise analysis of the data by first calculating distances, then looking for obvious three-point ordering conclusions, and finally proceeding to a complete crossover analysis. It reports results from each step of the analysis and an overall conclusion. COTRANS provides significant gains in speed and convenience over hand analysis, particularly for multipoint crosses with several recombinant classes.     

Variation in nuclear DNA content of isonicotinic acid hydrazide-resistant cell lines and mutant plants of Nicotiana tabacum

Summary Isonicotinic acid hydrazide (INH)-resistant lines of Nicotiana tabacum have been maintained in callus culture for six years and mutant plants have been regenerated from a number of these lines. This study examines variations in DNA content in nuclei of several of these callus cultures, regenerated plants, and secondary callus from the regenerated plants. The lines selected for study include three easily regenerated lines (I 21, I 24, and I 9) and two lines of poor regenerating capacity (I 1 and I 18). Two of the regenerating lines eventually led to fertile plants and the third produced only sterile plants. In general, the range of total nuclear variability was not as high as anticipated from other studies of long-term tobacco callus cultures. The majority of nuclei in all the distributions were between 3 and 20 pg, and the most frequently encountered distributions concentrated in the 7–18 pg region corresponding to 2–5C by our estimate of the C value for tobacco. Distributions were not identical for plants regenerated from the same culture simultaneously, and the nuclear DNA content of secondary callus cultures from one of the plants examined did not reflect the quantitative DNA pattern of the plant from which it was derived. The greatest degree of variability and highest DNA content for individual nuclei were observed in the primary callus of the poorly- and non-regenerating lines. The variability in DNA content was not associated with the INH-resistant trait.     

Altered glycine decarboxylation inhibition in isonicotinic Acid hydrazide-resistant mutant callus lines and in regenerated plants and seed progeny

Isonicotinic acid hydrazide (INH), an inhibitor of the photorespiratory pathway blocking the conversion of glycine to serine and CO₂, has been used as a selective agent to obtain INH-resistant tobacco (Nicotiana tabacum) callus cells. Of 22 cell lines that were INH-resistant, none were different from wild-type cells in their ability to take up [³H]INH or to oxidize INH to isonicotinic acid. In 7 of the 22 cell lines, INH resistance was associated with decreased inhibition of NAD-dependent glycine decarboxylation activity in isolated mitochondrial preparations. In the cell line that was most extensively investigated (I 24), this biochemical phenotype (exhibiting a 3-fold higher K_i with INH) was observed in leaf mitochondria of regenerated plants and of plants produced from them by self-fertilization. After crosses between resistant and sensitive plants, the decreased inhibition of glycine decarboxylation was observed among F₂ and backcross progeny only in those plants previously identified as INH-resistant by callus growth tests. In contrast, in siblings identified as INH-sensitive, glycine decarboxylation was inhibited by INH at the wild-type level. This demonstration of the transfer of an altered enzyme property from callus to regenerated plants and through seed progeny fulfills an important requirement for the use of somatic cell genetics to produce biochemical mutants of higher plants.     

Monoclonal antibodies to rabbit liver cytochrome P-448

Cytochrome P-448 (mol wt 55,000 Daltons) from rabbit liver was purified to a specific content of 16.6 nmol/mg. Mice were immunised with this preparation, their spleens removed and dissociated lymphocytes hybridised with myeloma cells. Four monoclonal antibodies against cytochrome P-448 were raised and partially characterised. All four antibodies interacted with cytochrome P-448 in intact microsomal fractions and selectively immunoadsorbed cytochrome P-448 from solubilised microsomal preparations. One of the antibodies inhibited benzo[a] pyrene hydroxylase activity in a reconstituted system, one had no effect on activity and two increased activity. The possible applications of such antibodies are discussed.