RESUMEN
Under experimental conditions, the growth of loblolly pine (Pinus taeda L.) is often responsive to ozone at near-ambient concentrations. However, little is known of the biochemical changes associated with this or other pollutants. Loblolly pine seedlings in open-top chambers were exposed to combinations of ozone (sub-ambient, ambient, or twice-ambient), acidic precipitation (pH 3.8 or pH 5.2) and soil magnesium (0.15 or 0.32 microg g(-1) exchangeable Mg) for three growing seasons. The effects of these treatments were greater in foliage than in stems or roots. The largest treatment effect was a 50% decrease in the starch concentration of current-year foliage from the twice-ambient ozone treatment compared with current-year foliage from the sub-ambient ozone treatment. Responses to ozone were consistent with the hypothesis that ozone-induced growth reductions are associated with depletion of carbohydrate reserves resulting from injury compensation and repair processes or reduced carbon fixation or both. Addition of acidic precipitation, and to a small extent Mg, decreased sugar concentrations of tissues; however, this effect appeared to be mediated by nutrient addition rather than by acidity per se. Given the role of carbohydrates in plant resistance to environmental stress, the sensitivity of carbohydrates to experimental treatments demonstrates the potential for indirect effects of ozone, acidic precipitation, and soil properties on stress resistance. Noncarbohydrate constituents were largely unresponsive to the experimental treatments. These findings imply that tissue carbohydrate analysis may be useful for assessing the impacts of pollutants in forest ecosystems.
RESUMEN
Mycorrhizal researchers are faced with the dilemma of designing experiments on small-scale processes that contribute to the solution of large-scale problems, such as global change. Hierarchy Theory provides a paradigm that indicates the need for mycorrhizal research and suggests criteria that help to prioritize research objectives. In general, mycorrhizal research is justified whenever direct or indirect effects on mycorrhizal physiology or ecology form a critical constraint to large-scale system function. The paper attempts to extract the relevant concepts from the theory and provides a series of illustrative examples from mycorrhizal research.
RESUMEN
White oak (Quercus alba L.) seedlings were grown from a half-sib collection of acorns in pots containing a nutrient-Poor forest soil and maintained in controlled-environment chambers having mean atmospheric CO2 concentrations of 389, 496, and 793 cm3 m-3 . Additions of nitrogen and phosphorus to the soil increased plant growth, indicating that the unfertilized plants were nutrient deficient. Despite the nutrient deficiency, the plants grown in elevated concentrations of CO., generally were larger than those in ambient CO2 , but dry weight data from harvests at 5, 12, 24, and 36 weeks provided insufficient evidence of an effect of CO2 because of the high variability associated with the recurrently-Hushing habit of these seedlings. Mathematical growth analysis based on periodic non-destructive measurements allowed comparisons of the continuous growth patterns of the plants and avoided the problems of ontogenetic variation. CO2 , enrichment was thus shown to increase plant growth rate primarily through increased unit leaf rate rather than increased leaf area production. Unit leaf rate during the second half of the experiment was 22 and 27% higher in the medium and high concentrations of CO2 compared with that in low CO 2 instantaneous measurements of foliar gas exchange also showed that CO2 , assimilation increased with CO2 , enrichment. The most pronounced effect of CO2 , enrichment was increased water-use efficiency, which was shown both through whole-plant gravimetric analysis and instantaneous gas exchange measurements. Whole-plant water-use efficiency for the duration of the experiment was increased by 52 and 82% by the mdium and high concentrations of CO2 . Limitations of resources, including water and nutrients, do not preclude plant growth responses to CO2 enrichment of the atmosphere.
RESUMEN
Increased exudation of carbon compounds from roots may provide a mechanism for enhancement of nutrient availability to plants growing in a CO(2)-enriched atmosphere. Therefore, the effect of atmospheric CO(2) concentration on carbon allocation and root exudation was investigated in Pinus echinata Mill. (shortleaf pine) seedlings. After 34 and 41 weeks, seedlings growing in 695 microl l(-1) CO(2) allocated proportionately more (14)C-labeled photosynthate to fine roots than did seedlings growing in ambient air. This was associated with greater fine root mass and mycorrhizal density in CO(2)-enriched plants after 34 weeks. Exudation of soluble, (14)C-labeled compounds from roots also was greater in these plants at 34 weeks, but the effect of CO(2) concentration on exudation did not persist at 41 weeks.
RESUMEN
The DNA sequence was determined for the cloned Thiobacillus ferrooxidans nifH and part of the nifD genes. A putative T. ferrooxidans nifH promoter was identified whose sequences showed perfect consensus with those of the Klebsiella pneumoniae nif promoter. Two putative consensus upstream activator sequences were also identified. The amino acid sequence was deduced from the DNA sequence. In a comparison of nifH DNA sequences from T. ferrooxidans and eight other nitrogen-fixing microbes, a Rhizobium sp. isolated from Parasponia andersonii showed the greatest homology (74%) and Clostridium pasteurianum (nifH 1) showed the least homology (54%). In a comparison of the amino acid sequences of the Fe proteins, the Rhizobium sp. and Rhizobium japonicum showed the greatest homology (both 86%) and C. pasteurianum (nifH 1 gene product) demonstrated the least homology (56%) to the T. ferrooxidans Fe protein.
Asunto(s)
Nitrogenasa/genética , Thiobacillus/genética , Secuencia de Aminoácidos , Secuencia de Bases , Clonación Molecular , ADN Bacteriano/análisis , Klebsiella pneumoniae/genética , Rhizobium/análisis , Thiobacillus/enzimologíaRESUMEN
A 2089-bp chromosomal DNA segment containing the Thiobacillus ferrooxidans glnA gene has been sequenced. Putative glnAp1-type promoter sequences, a consensus ntrC-gene-product-binding site and a catabolite-activating protein consensus recognition sequence were detected upstream of the structural gene. The glnA gene was followed by a sequence resembling a Rho-independent termination sequence. The complete amino acid sequence (468 residues) of the glutamine synthetase (GS) has been deduced, and comparisons are made with reported amino acid sequences of GS from other organisms.
Asunto(s)
Glutamato-Amoníaco Ligasa/genética , Thiobacillus/genética , Secuencia de Aminoácidos , Secuencia de Bases , Codón , Cianobacterias/genética , ADN Bacteriano/genética , Escherichia coli/genética , Células Eucariotas/fisiología , Genes BacterianosRESUMEN
One-year-old dormant white oak (Quercus alba L.) seedlings were planted in a nutrient-deficient forest soil and grown for 40 weeks in growth chambers at ambient (362 microliters per liter) or elevated (690 microliters per liter) levels of CO(2). Although all of the seedlings became severely N deficient, CO(2) enrichment enhanced growth by 85%, with the greatest enhancement in root systems. The growth enhancement did not increase the total water use per plant, so water-use efficiency was significantly greater in elevated CO(2). Total uptake of N, S, and B was not affected by CO(2), therefore, tissue concentrations of these nutrients were significantly lower in elevated CO(2). An increase in nutrient-use efficiency with respect to N was apparent in that a greater proportion of the limited N pool in the CO(2)-enriched plants was in fine roots and leaves. The uptake of other nutrients increased with CO(2) concentration, and P and K uptake increased in proportion to growth. Increased uptake of P by plants in elevated CO(2) may have been a result of greater proliferation of fine roots and associated mycorrhizae and rhizosphere bacteria stimulating P mineralization. The results demonstrate that a growth response to CO(2) enrichment is possible in nutrient-limited systems, and that the mechanisms of response may include either increased nutrient supply or decreased physiological demand.
RESUMEN
Morphological abnormalities including extra compound eyes, extra heads, and distally duplicated legs were generated in cricket embryos by treating eggs with single doses of either benz[g]isoquinoline-5,10-dione or benzo[h]quinoline-5,6-dione. Slight structural modifications of the molecules resulted in a loss of teratogenic activity, although embryotoxicity occurred. These potent insect teratogens can be used for analysis of developmental events during embryogenesis.