Phloem mobility of magnesium

Magnesium-28 was applied to specific leaves of bean (Phaseolus vulgaris) and barley (Hordeum vulgare) plants. After 24 hours, as much as 7% of the absorbed Mg was exported from the treated bean leaves and 11% was transported basipetally from the treated zone of the barley leaves. Transport of Mg did not occur past a heat-killed section of the treated leaf, thereby indicating that translocation took place via the phloem. Mg movement in the phloem was also evident in autoradiograms of bean stem segments in which the xylem was separated from the phloem by a thin sheet of plastic.     

C14 distribution in photosynthate of tomato as influenced by substrate copper and molybdenum level and nitrogen source

Summary The influence of nitrogen source and micronutrient treatment on the apportionment of C¹⁴ in alcohol extracts was studied in tomato. Plants were exposed at several stages of maturity to C¹⁴O₂ and the ethanol-soluble photosynthate fractionated into sugars, organic acids, and amino acids.Ammonium-treated plants had low levels of organic acids at all stages of maturity, suggesting a rapid conversion to amino acid residues. However, the addition of copper in the absence of molybdenum resulted in increased labelling of the organic acid fraction under nitrate nutrition. The amino acid fraction was reduced at some stages of growth under these conditions. This may indicate that copper interferes with the role of molybdenum in the enzymatic reduction of nitrate.Measurement of the total quantity of some individual free amino acids indicated more efficient utilization of these for protein synthesis in the presence of copper. On the other hand, assay of the C¹⁴-activity of individual free amino acids showed that degree of label bore little relation to micro-nutrient treatment.Plant Science Department and Botany Department, University of Connecticut. Scientific Contribution No. 116, Agricultural Experiment Station, University of Connecticut, Storrs. This paper is based on a portion of the senior author's Ph. D. thesis (University of Connecticut).     

Plasmodium gallinaceum: density dependent limits on infectivity to Aedes aegypti

In acute, blood-induced infections of chickens, the malarial parasite Plasmodium gallinaceum is most infective to the mosquito Aedes aegypti 1 day before gametocyte numbers peak. In an effort to account for this disynchrony , daily changes in parasite infectivity, parasitemia, hematocrit, and hemoglobin were measured during the course of infections. Three events were correlated with the loss of infectivity: (1) In the 24 hr between park infectivity and peak gametocytemia , schizont-induced hemolysis reduced the red blood cell volume 22%. (2) P. gallinaceum zygotes, fertilized in vitro and mixed with heavily infected red blood cells from which all viable, mature gametocytes had been removed, produced 67% fewer oocytes than when combined with uninfected red blood cells. (3) Zygotes fertilized in vitro on the day of peak parasitemia produced 47% fewer oocysts than zygotes prepared 24 hr earlier. It appears that high parasite density reduces infectiousness by destroying, through hemolysis and intraerythrocytic metabolism, a substance necessary to the sporogonic stages, and that there is also an intrinsic loss of infectivity, possibly due to decreased efficiency of fertilization.     

Supporting upper-level undergraduate students in building a systems perspective in a botany course

Undergraduate biology majors require biological literacy about the critical and dynamic relationships between plants and ecosystems and the effect human-made processes have on these systems. To support students in understanding systems relationships, we redesigned an undergraduate botany course using an ecological framework and embedded systems modelling to support students in understanding the criticality of plant processes to the global carbon cycle. The class meetings included lectures, opportunities to develop systems models identifying the relationships between plant processes and other systems, reflections on their systems understanding and open-floor discussions about assigned primary and secondary readings that explored the relationships between plant systems, abiotic and biotic processes and global carbon cycling in their systems models. We used the systems models students developed at the beginning and end of the course to examine how their systems understanding grew. Our results suggest that at the beginning of term, students’ ideas about plants were egocentric identifying the purpose of plants was to support human life and they did not consider relationships between plants and global carbon systems. By the end of the term, their models and reflections identified elements of a systems perspective and the students considered human impact on this delicate balance.     

Repair of O6-methylguanine adducts in human telomeric G-quadruplex DNA by O6-alkylguanine-DNA alkyltransferase

O⁶-alkylguanine-DNA alkyltransferase (AGT) is a single-cycle DNA repair enzyme that removes pro-mutagenic O⁶-alkylguanine adducts from DNA. Its functions with short single-stranded and duplex substrates have been characterized, but its ability to act on other DNA structures remains poorly understood. Here, we examine the functions of this enzyme on O⁶-methylguanine (6mG) adducts in the four-stranded structure of the human telomeric G-quadruplex. On a folded 22-nt G-quadruplex substrate, binding saturated at 2 AGT:DNA, significantly less than the ∼5 AGT:DNA found with linear single-stranded DNAs of similar length, and less than the value found with the telomere sequence under conditions that inhibit quadruplex formation (4 AGT:DNA). Despite these differences, AGT repaired 6mG adducts located within folded G-quadruplexes, at rates that were comparable to those found for a duplex DNA substrate under analogous conditions. Repair was kinetically biphasic with the amplitudes of rapid and slow phases dependent on the position of the adduct within the G-quadruplex: in general, adducts located in the top or bottom tetrads of a quadruplex stack exhibited more rapid-phase repair than did adducts located in the inner tetrad. This distinction may reflect differences in the conformational dynamics of 6mG residues in G-quadruplex DNAs.     

Diversity of lactic acid bacteria of the bioethanol process

Background  

Bacteria may compete with yeast for nutrients during bioethanol production process, potentially causing economic losses. This is the first study aiming at the quantification and identification of Lactic Acid Bacteria (LAB) present in the bioethanol industrial processes in different distilleries of Brazil.     

Dynamics of maternal and paternal effects on embryo and seed development in wild radish (Raphanus sativus)

Background and Aims

Variability in embryo development can influence the rate of seed maturation and seed size, which may have an impact on offspring fitness. While it is expected that embryo development will be under maternal control, more controversial hypotheses suggest that the pollen donor and the embryo itself may influence development. These latter possibilities are, however, poorly studied. Characteristics of 10-d-old embryos and seeds of wild radish (Raphanus sativus) were examined to address: (a) the effects of maternal plant and pollen donor on development; (b) the effects of earlier reproductive events (pollen tube growth and fertilization) on embryos and seeds, and the influence of embryo size on mature seed mass; (c) the effect of water stress on embryos and seeds; (d) the effect of stress on correlations of embryo and seed characteristics with earlier and later reproductive events and stages; and (e) changes in maternal and paternal effects on embryo and seed characteristics during development.

Methods

Eight maternal plants (two each from four families) and four pollen donors were crossed and developing gynoecia were collected at 10 d post-pollination. Half of the maternal plants experienced water stress. Characteristics of embryos and seeds were summarized and also compared with earlier and later developmental stages.

Key Results

In addition to the expected effects of the maternal plants, all embryo characters differed among pollen donors. Paternal effects varied over time, suggesting that there are windows of opportunity for pollen donors to influence embryo development. Water-stress treatment altered embryo characteristics; embryos were smaller and less developed. In addition, correlations of embryo characteristics with earlier and later stages changed dramatically with water stress.

Conclusions

The expected maternal effects on embryo development were observed, but there was also evidence for an early paternal role. The relative effects of these controls may change over time. Thus, there may be times in development when selection on the maternal, paternal or embryo contributions to development are more and less likely.     

Local forest structure variability increases resilience to wildfire in dry western U.S. coniferous forests

A ‘resilient’ forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine‐scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long‐lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that greater variability in forest structure increases resilience by reducing rates of fire‐induced tree mortality and that the scale of this effect is local, manifesting at the smallest spatial extent of forest structure tested (90 × 90 m). Resilience of these forests is likely compromised by structural homogenisation from a century of fire suppression, but could be restored with management that increases forest structural variability.     

The ontogeny of nursing in Babyrousa babyrussa and a comparison with domestic pigs

The nursing behavior of eight babirusa (Babyrousa babyrussa) infants was studied. Four were from single births and four were from twin births. The age at weaning, the time of day and number of nursing bouts per day, the mean duration of nursing bouts, and whether the offspring or the dam ended nursing bouts were all examined. It was found that although twins are weaned earlier than single offspring, there were no other statistically significant differences in nursing behavior of single and twin offspring. The ontogeny of nursing behavior in this species is described and some comparisons are made between the nursing behavior of babirusa and nursing in the domestic pig (Sus scrofa) and selected suids. Babirusa dams take longer to wean their offspring, allow them to nurse longer, and end nursing bouts less often than domestic pigs. The differences in behavior between babirusa and domestic pig nursing behavior may be related to differences in the number of offspring produced by the two species and the amount of parental investment in each offspring. Zoo Biol 19:253–262, 2000. © 2000 Wiley‐Liss, Inc.