Preferential transposition of aDrosophila P element to the corresponding region of the homologous chromosome

Genetic and physical analyses have demonstrated an intimate interaction or pairing of homologous chromosomes in the nuclei of manyDrosophila cell types. Experiments were performed to determine whether P elements transposing from a given chromosome to its homolog would preferentially insert in the region corresponding to the donor site, perhaps due to such a proximity. AP[lacZ;ry ⁺] element at thecactus locus (35F) on the second chromosome was mobilized and 96 insertions on the homolog were recovered. The distribution of these new insertions was determined by recombination mapping and molecular analysis, and compared with a control set of 93 second-chromosome insertions originating from theX chromosome. A nearly threefold preference was observed for re-insertion in a region of two to three number divisions aroundcactus on the homolog. However, none of these local insertions was actually within 50 kb of the site atcactus corresponding to the starting site. This is in marked contrast to the previously described phenomenon of intrachromosomal local transposition, where the majority of local transpositions are within 10 kb. The data suggest that the mechanisms for intrachromosomal and interchromosomal local transposition are distinct, and are consistent with a model for interchromosomal local transposition involving proximity of homologous chromosomal regions in the nuclei of the germline cells.     

Water relations,gas exchange,and growth of resprouts and mature plant shoots of Arbutus unedo L. and Quercus ilex L.

Resprout and mature plant shoot growth, leaf water status and gas exchange behavior, tissue nutrient content, flowering, and production were studied for co-occurring shallow-rooted (Arbutus unedo L.) and deeprooted (Quercus ilex L.) Mediterranean tree species at the Collserola Natural Park in Northeast Spain Resprouts showed higher growth rates than mature plant shoots. During fall, no differences in eco-physiological performance of leaves were found, but mobilization of carbohydrates from burls strongly stimulated growth of fall resprouts compared to spring resprouts, despite low exposed leaf area of the fall shoots. During summer drought, resprouts exhibited improved water status and carbon fixation compared to mature plant shoots. Shoot growth of Q. ilex was apparently extended due to deep rooting so that initial slower growth during spring and early summer as compared to A. unedo was compensated. Tissue nutrient contents varied only slightly and are postulated to be of minor importance in controlling rate of shoot growth, perhaps due to the relatively fertile soil of the site. Fall flowering appeared to inhibit fall shoot growth in A. unedo, but did not occur in Q. ilex. The results demonstrate that comparative examinations utilizing vegetation elements with differing morphological and physiological adaptations can be used to analyze relatively complex phenomena related to resprouting behavior. The studies provide an important multi-dimensional background framework for further studies of resprouting in the European Mediterranean region.     

Integrated nitrogen,carbon, and water relations of a xylem-tapping mistletoe following nitrogen fertilization of the host

Xylem-tapping mistletoes transpire large volumes of water (E) while conducting photosynthesis (A) at low rates, thus maintaining low instantaneous wateruse efficiency (A/E). These gas-exchange characteristics have been interpreted as a means of facilitating assimilation of nitrogen dissolved at low concentration in host xylem water; however, low A/E also results in substantial heterotrophic carbon gain. In this study, host trees (Juniperus osteosperma) were fertilized and gas exchange of mistletoe (Phoradendron juniperinum) and host were monitored to determine whether mistletoe A/E would approach that of the host if mistletoes were supplied with abundant nitrogen. Fertilization significantly increased foliar N concentrations (N), net assimilation rates, and A/E in both mistletoe and host. However, at any given N concentration, mistletoes maintained lower A and lower A/E than their hosts. On the other hand, when instantaneous water-use efficiency and A/N were calculated to include heterotrophic assimilation of carbon dissolved in the xylem sap of the host, both water-use efficiency and A/N converged on host values. A simple model of Phoradendron carbon and nitrogen budgets was constructed to analyze the relative benefits of nitrogen- and carbonparasitism. The model assumes constant E and includes feedbacks of tissue nitrogen concentration on photosyn-thesis. These results, combined with our earlier observation that net assimilation rates of mistletoes and their hosts are approximately matched (Marshall et al. 1994), support part of the nitrogen-parasitism hypothesis: that high rates of transpiration benefit the mistletoe primarily through nitrogen gain. However, the low ratio of A/E is interpreted not as a means of acquiring nitrogen, but as an inevitable consequence of an imbalance in C and N assimilation.This research was supported by the National Science Foundation (grants BSR-8706772 and 8847942).     

The effects of tail autotomy on survivorship and body growth of Uta stansburiana under conditions of high mortality

We examined the effects of tail autotomy on survivorship and body growth of both adult and juvenile Uta stansburiana by directly manipulating tail condition. Tail loss decreased neither survivorship nor rate of body growth for individuals in two natural populations. Lack of an influence of tail loss on survivorship in these two populations may be the result of high mortality. Under high mortality any differential effects of tail loss will be lower than in populations facing lower mortality. Growth experiments in the laboratory demonstrated that, under conditions of minimal environmental variation and social interactions, there is no tradeoff between body growth and tail regeneration as has been suggested for other species of lizards. One possible reason for this difference is that U. stansburiana does not use the tail as a storage organ for lipids. The original and regenerated tails are composed mainly of protein. In general, any differential body growth between tailed and tailless individuals may be due to social interactions and not a diversion of limited energy into tail regeneration.     

Reproductive variation and the egg size-clutch size trade-off within and among populations of painted turtles (Chrysemys picta bellii)

Interpopulation variation in egg size, clutch size and clutch mass was studied 3 years in four populations of painted turtles (Chrysemys picta bellii) from western Nebraska. Body size varied among all populations and was larger in two large (56–110 ha), sandhills lake populations than in two populations in smaller habitats (1.5–3.6 ha) of the Platte River floodplain. Reproductive parameters (egg mass, clutch mass, and clutch size) generally increased with maternal body size within populations. Clutch wet and dry mass varied among populations but largely as a function of maternal body size. Clutch size was largest in the sandhills lake populations, both absolutely and relative to maternal body size. Egg mass was smallest in the sandhills lakes and varied annually in one population. Over all populations, an egg sizeclutch size trade-off was detected (a negative correlation between egg mass and clutch size) after statistically removing maternal body size effects. Egg wet mass and clutch size were negatively correlated over all years within the sandhills populations and in some years in three populations. Although egg size varied within populations, egg size and clutch size covaried as expected by optimal offspring size models. Thus, patterns of egg size variation should be interpreted in the context of proximate or adaptive maternal body size and temporal effects. Comparisons among populations suggest that large egg size relative to maternal body size may occur when juvenile growth potential is poor and mean maternal body size is small.     

Soil pCO2, soil respiration,and root activity in CO2-fumigated and nitrogen-fertilized ponderosa pine

The purpose of this paper is to describe the effects of CO₂ and N treatments on soil pCO₂, calculated CO₂ efflux, root biomass and soil carbon in open-top chambers planted with Pinus ponderosa seedlings. Based upon the literature, it was hypothesized that both elevated CO₂ and N would cause increased root biomass which would in turn cause increases in both total soil CO₂ efflux and microbial respiration. This hypothesis was only supported in part: both CO₂ and N treatments caused significant increases in root biomass, soil pCO₂, and calculated CO₂ efflux, but there were no differences in soil microbial respiration measured in the laboratory. Both correlative and quantitative comparisons of CO₂ efflux rates indicated that microbial respiration contributes little to total soil CO₂ efflux in the field. Measurements of soil pCO₂ and calculated CO₂ efflux provided inexpensive, non-invasive, and relatively sensitive indices of belowground response to CO₂ and N treatments.     

Genetic manipulation of 6-phosphofructokinase in potato tubers

The aim of this work was to discover whether genetic manipulation of 6-phosphofructokinase [EC 2.7.1.11; PFK(ATP)] influenced the rate of respiration of tuber tissue of Solanum tuberosum L. Transgenic plants were produced that contained the coding sequence of the Escherichia coli pfkA gene linked to a patatin promoter. Expression of this chimaeric gene in tubers resulted in a 14to 21-fold increase in the maximum catalytic activity of PFK(ATP) without affecting the activities of the other glycolytic enzymes. Tubers, and aged disks of tuber tissue, from transformed plants showed no more than a 30% fall in the content of hexose 6-monophosphates; the other intermediates of glycolysis increased threeto eightfold. Fructose-2,6-bisphosphate was barely detectable in aged disks of transformed tubers. The relative rates of ¹⁴CO₂ production from [1-¹⁴C]-and [6-¹⁴C]-glucose supplied to disks of transformed and control tubers were similar. Oxygen uptake and CO₂ production by aged disks of transformed tubers did not differ significantly from those from control tubers. The same was true of CO₂ production, in air, and in nitrogen, for tuber tissue. It is concluded that PFK(ATP) does not dominate the control of respiration in potato tubers.Abbreviations Fru2,6bisP fructose-2,6-bisphosphate - FW freshweight - GUS -glucuronidase - PFK(ATP) 6-phosphofructokinase - PFK(PPi) pyrophosphate: fructose-6-phosphate 1-phosphotransferase     

Phenyllactic acid but not tropic acid is an intermediate in the biosynthesis of tropane alkaloids in Datura and Brugmansia transformed root cultures

(S)-(-)-Tropic acid is the acidic moiety of the tropane ester alkaloids, hyoscyamine and scopolamine (hyoscine). When tropic acid is fed to transformed root cultures of Datura stramonium L. or a Brugmansia (Datura) Candida x B. aurea hybrid, the formation of these alkaloids is inhibited. Phenyllactic acid, from which the tropoyl moiety is derived, is considerably less inhibitory. Label from (RS)-phenyl[1,3-¹³C₂]lactic acid is incorporated at high levels into apoatropine, littorine, aposcopolamine, hyoscyamine, 7-hydroxyapoatropine, scopolamine and 7-hydroxyhyoscyamine when fed to these cultures. The presence of an excess concentration of unlabelled tropic acid has little influence on the specific incorporation into these products. It is concluded that free tropic acid is not an intermediate in hyoscyamine biosynthesis but rather that the rearrangement of phenyllactic acid occurs subsequent to its esterification.Abbreviations FM fresh mass - NMR nuclear magnetic resonance spectroscopy We are grateful to Drs. N.J. Walton, A.J. Parr, M.J.C. Rhodes (Institue of Food Research, Norwich) and B. Dräger (Münster, Germany) for helpful and critical discussions. We also wish to thank Dr. P. Bachmann (Braunschweig, Germany) for suggesting the use of the DB-17 column to separate littorine from hyoscyamine and for the modified Excel programme used to calculate the specific incorporations, Yannick Ford (AFRC Co-operative Award Studentship, University of Oxford) and Abigael Peerless for their able assistance, Dr. I. Colquhoun for assistance with some of the NMR spectroscopy and Drs. K. Shimomura (Tsukuba, Japan) and T. Hashimoto (Kyoto, Japan) for pure samples of 7-hydroxyhyoscyamine. J.G.W, gratefully acknowledges support from the Nuffield Foundation under the Small Grants Scheme to promote collaborative experimentation and M.A. is grateful to the Ministry of Education, Iran for a research scholarship.     

Fruiting of ectomycorrhizal basidiomycetes on unburned and prescribed burned hard-pine/hardwood plots after drought-breaking rainfalls on the Allegheny Mountains of southwestern Virginia

A headfire upward along the crest to the peak of a foothill during February 1988 had been prescribed to lower the possibility of a wildfire during the dry season on the Jefferson National Forest. Some surface litter plus annual and perennial stems on one-half of a stand of Pinus pungens/P. rigida had been destroyed. Subsequent development of ectomycorrhizal sporophores of basidiomycetes was recorded regularly within equal areas of burned and unburned portions and within a nearby unburned stand of P. virginiana. Each plot had a few ectomycorrhizal hardwoods, mainly Quercus spp. First fruiting was noted under burned P. pungens 3 weeks after a general rain in mid-July and after 4 weeks under both. By the end of November, when fruiting ceased, 138 separable taxa had been collected of which 95 had been identified. A list of the fungi and data on current and previously reported host associations, occurrence on each of the substrates, times and frequencies of fruiting, periodicity of genera, and variations in weather conditions are presented.