自然免耕下的稻田生态系统

自然免耕是一种新型的稻田耕作法,通过人为改变地表微地形,建立了一个适合水旱作物复种轮作,鱼、萍、鸭周年共生的稻田生态系统．自然免耕促进了土壤内、外环境的物质、能量和信息交换,水、热、气、肥谐调．并通过环境网络效应,强化了环境与生物区系间的缓冲－调节力．提高了土壤自调能力和土壤有序度．     

1H Nuclear Magnetic Resonance Spectroscopy Study of Cerebral Glutamate in an Ex Vivo Brain Preparation of Guinea Pig

Abstract: Cerebral glutamate was monitored in a superfused cerebral cortical preparation by ¹H NMR spectroscopy using a semiselective spin-echo sequence N -acetyl aspartate (NAA) as an internal concentration reference. During controlled metabolic conditions, the cerebral ¹H NMR-detected glutamate-to-NAA ratio was ∼ 20–30% lower than expected from the ratio of neutralized perchloric acid extracts of the preparations. Inhibition of respiration in the presence of glucose did not change the ¹H NMR glutamate-to-NAA ratio in brain slice preparation. In contrast, either complete depletion of ATP during cyanide poisoning together with 0 m M glucose, anoxia in the absence of glucose, or treatment with nigericin or with a protonophore, carbonyl cyanide- m -fluorophenylhydrazone, increased ¹H NMR-detected glutamate/NAA in the cerebral preparations without a change in the relative and absolute concentration ratios determined from the tissue acid extracts. Spin-spin relaxation times of glutamate and NAA peaks in anoxic slices were 749 ± 89 and 729 ± 94 ms, respectively, and thus, the portion of glutamate that could not be detected by ¹H NMR was quantified in absolute terms. It was calculated that an increase in the glutamate-to-NAA ratio from 0.55 ± 0.02 to 0.67 ± 0.02 during aglycemic anoxia corresponded to some 6 mmol/kg of tissue dry weight of glutamate from the total concentration of 28 mmol/kg dry weight. It is suggested that this 22% of total glutamate pool is present in a noncytoplasmic compartment during controlled metabolic state.     

Cerebral Metabolic Compartmentation as Revealed by Nuclear Magnetic Resonance Analysis of D-[1-13C]Glucose Metabolism

Abstract: Nuclear magnetic resonance (NMR) was used to study the metabolic pathways involved in the conversion of glucose to glutamate, γ-aminobutyrate (GABA), glutamine, and aspartate. d -[1^-13C]Glucose was administered to rats intraperitoneally, and 6, 15, 30, or 45 min later the rats were killed and extracts from the forebrain were prepared for ¹³C-NMR analysis and amino acid analysis. The absolute amount of ¹³C present within each carbon-atom pool was determined for C-2, C-3, and C-4 of glutamate, glutamine, and GABA, for C-2 and C-3 of aspartate, and for C-3 of lactate. The natural abundance ¹³C present in extracts from control rats was also determined for each of these compounds and for N-acetylaspartate and taurine. The pattern of labeling within glutamate and GABA indicates that these amino acids were synthesized primarily within compartments in which glucose was metabolized to pyruvate, followed by decarboxylation to acetyl-CoA for entry into the tricarboxylic acid cycle. In contrast, the labeling pattern for glutamine and aspartate indicates that appreciable amounts of these amino acids were synthesized within a compartment in which glucose was metabolized to pyruvate, followed by carboxylation to oxaloacetate. These results are consistent with the concept that pyruvate carboxylase and glutamine synthetase are glia-specific enzymes, and that this partially accounts for the unusual metabolic compartmentation in CNS tissues. The results of our study also support the concept that there are several pools of glutamate, with different metabolic turnover rates. Our results also are consistent with the concept that glutamine and/or a tricarboxylic acid cycle intermediate is supplied by astrocytes to neurons for replenishing the neurotransmitter pool of GABA. However, a similar role for astrocytes in replenishing the transmitter pool of glutamate was not substantiated, possibly due to difficulties in quantitating satellite peaks arising from ¹³C-¹³C coupling.     

Electrophoretic karyotypes of the elm tree pathogen Ophiostoma ulmi (sensu lato)

Pulsed field gel electrophoresis using OFAGE, TAFE, and CHEF systems has been used to more fully characterize karyotypic variation within the two closely related fungal species of Ophiostoma ulmi sensu lato. Twelve wild-type and laboratory strains, representing the less agressive species O. ulmi and both of the biotypes of the more aggressive species O. novo-ulmi were studied and their karyotypes determined. Depending on the strain, a minimum of four to a minimum of eight chromosomal DNA bands were present that fall into three distinct size classes, with one exception. Strain CESSI6K (O. novo-ulmi, North American aggressive subgroup) contains a unique chromosomal DNA band which comigrated near a Saccharomyces cerevisiae chromosome of 0.95 Mb. This unique band was the smallest O. ulmi s. l. chromosomal DNA observed. Seven of the twelve strains shared a common chromosomal DNA banding pattern, whereas each of the other five had a unique karyotype. There was no correlation between chromosome profile and species, as some O. novo-ulmi and O. ulmi strains shared common electrophoretic karyotypes.     

H assignment and secondary structure determination of human melanoma growth stimulating activity (MGSA) by NMR spectroscopy

The solution structure of melanoma growth stimulating activity (MGSA) has been investigated using proton NMR spectroscopy. Sequential resonance assignments have been carried out, and elements of secondary structure have been identified on the basis of NOE, coupling constant, chemical shift, and amide proton exchange data. Long-range NOEs have established that MGSA is a dimer in solution. The secondary structure and dimer interface of MGSA appear to be similar to those found previously for the homologous chemokine interleukin-8 [Clore et al. (1990) Biochemistry 29, 1689-1696]. The MGSA monomer contains a three stranded anti-parallel β-sheet arranged in a ‘Greek-key’ conformation, and a C-terininal -helix (residues 58 69).     

The effects of calcium deficiency on Cucurbita pepo L. hypocotyl cells: A 31P nuclear-magnetic-resonance study

Calcium deficiency in zucchini (Cucurbita pepo L.) is associated with reduced growth and a reduced ability to transport auxin (Allan and Rubery, 1991, Planta 183, 604–612). An investigation of the effects of calcium-deficiency on zucchini hypocotyl cells was made using weak-acid uptake and ³¹P-nuclear-magneticresonance (³¹P-NMR) spectroscopy in vivo and in tissue extracts. Calcium-deficient tissue had the same cytoplasmic and vacuolar pHs as normal tissue when extracellular pH was near neutral. At acidic external pH the vacuolar pH was lower in deficient tissue. Adenine nucleotides were present predominantly as ATP in both control and calcium-deficient tissues. Addition of calcium to calcium-deficient tissue, under conditions which cause recovery of auxin transport induced no changes in the ³¹P-NMR spectra of deficient tissue. The content of mobile, phosphorylated metabolites was reduced in calcium-deficient tissue in comparison to control tissue. However, a substantial increase in the content of phosphorylcholine occurs in calcium-deficient tissues compared with controls; this may reflect changes in lipid turnover in calcium-stressed cells. We wish to thank Drs. Terry Moore and Jamie Vandenberg for technical assistance and Professor Peter Morris for providing the gated oxygen device. A.C.A. thanks the Cambridge Commonwealth Trust for a Prince of Wales Scholarship and the O.R.S. Awards Scheme for an award.     

31P-Nuclear magnetic resonance spectroscopy study of the time course of energy metabolism during exercise and recovery

This study evaluated the time courses of intracellular pH and the metabolism of phosphocreatine (PCr) and inorganic phosphate (P) at the onset of four exercise intensities and recoveries. Non-invasive evaluation of continuous changes in phosphorus metabolites has become possible using³¹P-nuclear magnetic resonance spectroscopy (³¹P-MRS). After measurements at rest, six healthy male subjects performed 4 min of femoral flexion exercise at intensities of 0 (loadless), 10, 20 and 30 kg · m · min^–1 in a 2.1 T superconducting magnet with a 67-cm bore. Measurements were continuously made during 5 min of recovery. During a series of rest-exercise-recovery procedures,³¹P-MRS were accumulated using 32 scans · spectrum^–1 requiring 12.8 s each. At the onset of exercise, PCr decreased exponentially with a time constant of 27–32 s regardless of the exercise intensity. The time constant PCr resynthesis during recovery was about 27–40 s. The PCr kinetics were independent of exercise intensity. There were similar Pi kinetics at the onset of all types of exercise, while those of Pi recovery became significantly longer at the higher exercise intensities (P < 0.05). Furthermore, the intracellular pH indicated temporary alkalosis just at the onset of exercise, probably due to absorption of hydrogen ions by PCr hydrolysis, and then decrease at a point about 40%–50% of the preexercise PCr. The pH recovery time was longer than that for the P_i or PCr kinetics. By using a more efficient resolution system it was possible to obtain the phosphorus kinetics during exercise and to follow PCr resynthesis within the first few minutes of recovery. From our results it was concluded that in general the time course of PCr and Pi metabolism were unaffected by the exercise intensity, both at the onset of exercise and during recovery, with the exception of P_i recovery.     

Changes in intracellular pH during repeated exercise

The rates of change in intracellular pH during repeated exercise sessions with rest periods was determined by 31 phosphorus-nuclear magnetic resonance spectroscopy (³¹P-MRS). Five long-distance runners and six healthy male subjects as controls performed a 2-min femoral flexion at 20 kg · m · min^–1 in a 2.1 T superconducting magnet with a 67-cm bore and repeated this exercise four times with 2-min rest periods intervening. In all cases during exercise the inorganic phosphate (P_i) peak split into two, the earlier increased rapidly (high-pH P_i) and the later (low-pH P_i) increased more slowly. The P_i peaks were separated by a fitting procedure using the least square mean method. The high-pH P_i area during exercise decreased as the number of repeated exercise periods increased, while the low-pH P_i area gradually increased. Although the total P_i area decreased exponentially during the recovery period, the high-pH P_i area decreased first and then the low-pH P_i area reduced gradually. The pH values were estimated from the chemical shift between the phosphocreatine peak and each split peak in the P_i. The high-pH in pooled data ranged from 6.6 to 7.0 during exercise and recovery, while the low pH decreased to 6.2 during exercise. As the number of exercise periods increased, each pH value gradually became less acidic, although there was a tendency to more acidity in the control subjects than in the long-distance runners. In conclusion, it was possible to obtain by non-invasive, continuous³¹P-MRS, a split pattern of P_i peaks during exercise and there were at least tow different intracellular pH values during exercise, suggesting that each P_i peak might be attributed to the types of muscle fibre recruited.     

赣榆县厉庄地埂利用型式试验

在赣榆县厉庄以大金鸡菊、紫穗槐和红柳三种经济植物进行了地埂利用型式试验,取得了比较明显的水土保持效果和改善农田小环境的生态效益。栽植后第三年植物覆盖率达90％或100％;地面蒸发量减少15.2～17.7％;截留降水量为0.5～0.7mm;大气相对湿度提高3.7～5.4％;土壤养分也有不同程度的增加。经济效益估测每亩地埂可收到300～600元,比种黄豆高5～9倍。效益最好的是红柳,大金鸡菊次之,紫穗槐较低。     

Hearing in honeybees: localization of the auditory sense organ

Airborne sound signals emitted by dancing honeybees (Apis mellifera) contain information about the locations of food sources. Honeybees can perceive these near field sounds and rely on them to decode the messages of the dance language. The dance sound is characterized by rhythmical air particle movement of high velocity amplitudes. The aim of the present study was to identify the sensory structures used to detect near field sound signals. In an operant conditioning experiment, bees were trained to respond to sound. Ablation experiments with these trained bees revealed that neither mechanosensory hairs on the antennae or head nor bristle fields at the joints of the antenna, but Johnston's organ, a chordotonal organ in the pedicel of the antenna, is used to detect near field sound in honeybees.