云南省自然休闲地与桤木休闲地地上部分生物量与养分蓄积量的研究

通过样方调查和采样 ,对云南省西盟县新厂乡阿莫村自然条件相似、经历了相同休闲年限的桤木休闲地和自然休闲地的地上部分植被生物量和养分蓄积量进行了比较研究 ,结果表明 ,休闲 3a后 ,桤木休闲地的休闲效果显著高于自然休闲地。表现在桤木休闲地的地上部分生物量高于自然休闲地 ,休闲 6 a后 ,桤木林的地上部分生物量干重达到 6 9,6 4 0 kg/hm2 ,是自然休闲地的 4倍 ;桤木休闲地 N、P、K三大营养元素的地上部分蓄积量 ,经过 2～ 3a超过自然休闲地 ,并在休闲 3a后显著高于自然休闲地 ,休闲 6 a后 ,N蓄积量达到 5 5 7kg/hm2 ,是自然休闲地的 3倍 ,P、K的蓄积量分别达到 4 1kg/hm2 、2 6 5 kg/hm2 ,是自然休闲地的 2倍。目前研究说明桤木种植有改进轮歇农业的明显作用 ,具有在类似地区推广应用的价值。     

Calcium Oxalate Deposits in Leaves of Corchorus olitorius as Related to Accumulation of Toxic Metals1

This study was to report and describe the formation of Ca oxalate crystals and to explore whether there is any correlation between their abundant formation and the ability of plant to uptake and accumulate high levels of toxic metals. Soil-grown Corchorus olitorius L. (Tiliaceae) seedlings were further grown in water culture in the presence of Cd, Pb, Cu, or Al (0–10 g/ml) for 20 days. Light and electron microscopic examinations revealed a large number of intracellular prismatic-shaped Ca oxalate crystals in both leaf and callus cells. Crystals were formed in the vacuole, a single large crystal being formed per cell. The crystal-containing cells differed in size and shape from crystal-free cells, they were rich in organelles, membranes, and vesicles and have dense cytoplasm, enlarged nucleus and modified starch-lacking plastids with few grana. These cells look highly active. Corchorus plants treated with Cd, Pb, Cu, and Al accumulated these metals to the levels several times higher than untreated plants. The contents of Pb, Cd, Al, and Cu in leaf tissues of plants grown in the presence of 5 g/ml of these metals were 10, 20, 25, and 40 times higher, respectively, than those in plants grown on media devoid of them. X-ray microanalysis of Ca oxalate crystals in leaves from plants exposed to 5 g/ml Cd, Pb, Al, or Cu indicated the incorporation only of Al into these crystals. Results of this paper suggest a possible contribution for Ca oxalate-crystal formation in sequestering and tolerance of at least some toxic metals.     

Tubular invaginations in cerebral endothelium and their relation to smooth-surfaced cisternae in hagfish (Myxine glutinosa)

Summary The organization of vesicular profiles in the endothelium of cerebral capillaries of the hagfish, Myxine glutinosa, has been reinvestigated. Judged from random thin sections the endothelial cells contain numerous vesicles and tubules, in contrast to brain endothelia of most other vertebrates. However, three-dimensional reconstructions based on ultrathin serial sections (thickness 18 nm) showed that the profiles represent a system of irregular tubular invaginations of the cell membrane, comparable to the vesicular invaginations demonstrated in extracerebral capillary endothelia of frogs and rats. In addition, smooth-surfaced cisternae were present in close relation to the invaginations. The function of endothelial invaginations is unknown. They do not transport macromolecules, because the blood-brain barrier is practically impermeable to proteins. However, since the system of the invaginations and smooth-surfaced cisternae is structurally similar to the system of caveolae and sarcoplasmic reticulum in smooth muscle cells, a common function seems likely. It is proposed that endothelial invaginations and smooth-surfaced cisternae are involved in regulation of cytosolic Ca⁺⁺-concentration.     

Copper ions and hydrogen peroxide form hypochlorite from NaCl thereby mimicking myeloperoxidase

Sea urchins have elaborated multiple defenses to assure monospermic fertilization. In this work, we have concentrated on a study of the mechanism(s) by which hydrogen peroxide (H₂O₂) prevents polyspermy in Arbacia punctulata. We found that it is not H₂O₂ but probably hypochlorous acid/hypochlorite (HOCl/OCl^?) derived from H₂O₂ that is toxic to the supernumerary sperm. The spermicidal activity of H₂O₂ is potentiated by at least one order of magnitude by cupric ions (Cu²⁺). This increased toxicity is not due to the formation of hydroxyl radicals (·OH) because ·OH scavengers did not counteract the activity of Cu²⁺. More-over, substitution of Cu²⁺ by ferrous ions (Fe²⁺), which are known to cause formation of ·OH from H₂O₂, had no effect on fertilization even at 10²?10³ times higher concentrations. In contrast, 3-amino-1,2,4-triazole (AT), an HOCl/OCl^? scavenger, totally reversed the toxic effects of Cu²⁺. Furthermore, we found that HOCl/OCl^? is generated in solutions of H₂O₂ and Cu²⁺ in the presence of 0.5 M NaCl and that its accumulation is abolished by AT. Thus it is possible that the antifertility properties of copper are due to its ability to mediate formation of HOCl/OCl^?. HOCl/OCl^? generated by Cu²⁺ from H₂O₂ and Cl^?, a low concentration of exogenously added HOCl/OCl^?, or increased concentrations of H₂O₂ has similar inhibitory effects on the fertilization process in sea urchins. Therefore, we suggest that polyspermy is prevented by the action of a myeloperoxidase that affects the formation of HOCl/OCl^? from the Cl^? present in sea water through reaction with H₂O₂ generated by the newly fertilized egg.     

Photosynthetic inorganic carbon utilization and growth of Porphyra linearis (Rhodophyta)

Photosynthetic (oxygen evolution) and growth (biomass increase) responses to ambient pH and inorganic carbon (Ci) supply were determined for Porphyralinearis grown in 0.5 L glass cylinders in the laboratory, or in 40 L fibreglass outdoor tanks with running seawater. While net photosynthetic rates were uniform at pH 6.0–8.0, dropping only at pH 8.7, growth rates were significantly affected by pH levels other than that of seawater (c. pH 8.3). In glass cylinders, weekly growth rates averaged 76% at external pH 8.0, 13% at pH 8.7 and 26% at pH 7.0. Photosynthetic O₂ evolution on a daily basis(i.e. total O₂ evolved during day time less total O₂ consumed during night time) was similar to the growth responses at all experimental pH levels, apparently due to high dark respiration rates measured at acidic pH. Weekly growth rates averaged 53% in algae grown in fibreglass tanks aerated with regular air (360 mg L_-1 CO₂) and 28% in algae grown in tanks aerated with CO₂-enriched air (750 mg L^-1 CO₂). The pH of the seawater medium in which P. linear is was grown increased slightly during the day and only rarely reached 9.0. The pH at the boundary layer of algae submerged in seawater increased in response to light reaching, about pH 8.9 within minutes, or remained unchanged for algae submerged in a CO₂-free artificial sea water medium. Photosynthesis of P. linearissaturated at Ci concentrations of seawater (K_0.5560 μM at pH 8.2) and showed low photosynthetic affinity for CO₂(K_0.5 61 μM) at pH 6.0. It is therefore concluded that P. linearisuses primarily CO₂ with HCO₃ ^- being an alternative source of Ci for photosynthesis. Its fast growth could be related to the enzyme carbonic anhydrase whose activity was detected intra- and extracellularly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lipid biosynthesis in cultures of oilseed rape

Summary This review focuses on how microspore-derived (MD) embros and cell suspension cultures of oilseed rape have been used to advance our understanding of the biochemistry and molecular biology of lipid biosynthesis in plants. Both types of cultures are easily maintained and circumvent the difficulties associated with using developing seeds for investigations of lipid biosynthesis. Developing MD embryos exhibit a similar storage lipid accumulation profile and fatty acid composition to developing seed. The use of dihaploids derived from plantlets of MD embryos have accelerated breeding programs and have proven useful in the detection of recessive mutations. MD embryos and MD cell suspension cultures have been particularly useful in investigating the properties of key enzymes involved in triacylglycerol (TG) bioassembly. MD cell suspension cultures, however, offer the advantage of being able to study lipid metabolism in the absence of cellular differentiation. TG accumulation can be induced in MD cell suspension cultures by increasing the sucrose concentration of the growth medium thereby providing a useful system to investigate gene expression and the proteomics of lipid biosynthesis.     

Towards a model of non-equilibrium binding of metal ions in biological systems

We have used a systems biology approach to address the hitherto insoluble problem of the quantitative analysis of non-equilibrium binding of aqueous metal ions by competitive ligands in heterogeneous media. To-date, the relative proportions of different metal complexes in aqueous media has only been modelled at chemical equilibrium and there are no quantitative analyses of the approach to equilibrium. While these models have improved our understanding of how metals are used in biological systems they cannot account for the influence of kinetic factors in metal binding, transport and fate. Here we have modelled the binding of aluminium, Al(III), in blood serum by the iron transport protein transferrin (Tf) as it is widely accepted that the biological fate of this non-essential metal is not adequately described by experiments, invitro and insilico, which have consistently demonstrated that at equilibrium 90% of serum Al(III) is bound by Tf. We have coined this paradox ‘the blood-aluminium problem’ and herein applied a systems biology approach which utilised well-found assumptions to pare away the complexities of the problem such that it was defined by a comparatively simple set of computational rules and, importantly, its solution assumed significant predictive capabilities. Here we show that our novel computational model successfully described the binding of Al(III) by Tf both at equilibrium and as equilibrium for Al_Tf was approached. The model predicted significant non-equilibrium binding of Al by ligands in competition with Tf and, thereby, provided an explanation of why the distribution of Al(III) in the body cannot be adequately described by its binding and transport by Tf alone. Generically the model highlighted the significance of kinetic in addition to thermodynamic constraints in defining the fate of metal ions in biological systems.     

Rats Generate Vibrissal Sensory Evidence until Boundary Crossing Triggers a Decision

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