Nutrient dynamics in crown tissues of cork-oak (Quercus suber L.)

The seasonal fluctuation of N, P, K, Ca and Mg in leaves, young stems and fruits of young and matureQuercus suber trees growing at the same site was studied. Nutrient dynamics within the tree appeared to be linked to phenological events. Leaves maximized their nutrient contents throughout summer whereas stems maintained rather constant values during most of the year. Before the spring growth flush they apparently acted as temporary reservoirs for some nutrients, translocated from leaves or other organs, so that such nutrients would be easily invested in the new tissues. A significant investment was made in sink organs like flowers and fruits. The tree probably relies not only on leaves but also on other nutrient reservoirs like older branches and roots for an adequate supply to those sinks and to the spring growth. The importance of the sampling dates and the basis of expression used for nutrient concentrations has also been emphasized. Nutrient contents and seasonal trends of the studied trees were similar to those of other evergreen oaks, although somewhat higher values for N, K, and Mg were found. Moreover, soil nutrient contents in the studied 60m60/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">montado60m60/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> were much lower than in other Iberic oak stands. However the nutrient status and requirements of cork-oak suggest high (or at least adequate) nutrient availability to the trees. The mechanisms by which this could be achieved are discussed.     

Inhibition of lipid peroxidation

Lipid peroxy radicals (ROO-) were detected by electron spin resonance (ESR) at low temperature after formation by addition of H₂O₂ into a suspension of mice lymphocites. If lymphocytes were treated with selenomethionine (Se-Met) prior to addition of H₂O₂, ROO-formation was inhibited in a fashion that was dependent on Se-Met concentration. Formation of ROO- in the spleen of mice was induced by⁶⁰Co irradiation. Animals that were supplemented with Na₂SeO₃ prior to irradiation exhibited a lower ROO-concentration than that of nontreated animals. Based on our experiments, we have concluded that Se has an oxygen-free radical scavenging effect. This should be a protective effect against lipid peroxy radical cellular attack.     

Plasma Membrane Ubiquinone Controls Ceramide Production and Prevents Cell Death Induced by Serum Withdrawal

Serum provides cultured cells with survival factors required to maintain growth. Its withdrawal induces the development of programmed cell death. HL-60 cells were sensitive to serum removal, and an increase of lipid peroxidation and apoptosis was observed. Long-term treatment with ethidium bromide induced the mitochondria-deficient °HL-60 cell line. These cells were surprisingly more resistant to serum removal, displaying fewer apoptotic cells and lower lipid peroxidation. HL-60 cells contained less ubiquinone at the plasma membrane than °HL-60 cells. Both cell types increased plasma membrane ubiquinone in response to serum removal, although this increase was much higher in ° cells. Addition of ubiquinone to both cell cultures in the absence of serum improved cell survival with decreasing lipid peroxidation and apoptosis. Ceramide was accumulated after serum removal in HL-60 but not in °HL-60 cells, and exogenous ubiquinone reduced this accumulation. These results demonstrate a relationship between ubiquinone levels in the plasma membrane and the induction of serum withdrawal induced apoptosis, and ceramide accumulation. Thus, ubiquinone, which is a central component of the plasma membrane electron transport system, can represent a first level of protection against oxidative damage caused by serum withdrawal.     

Definition of a Sequence Unique in βII Spectrin Required for Its Axon-Specific Interaction with Fodaxin (A60)

Abstract: Spectrin isotypes segregate in neurons and are differentially distributed between axons and somatodendritic compartments. Their functions in those compartments are likely to be mediated by proteins that interact selectively with one or other isotype. Fodaxin (an axon-specific protein previously termed A60) colocalizes in CNS neurons with axonal spectrin and in vitro binds brain spectrin (a mixture of αI, βI, αII, and βII polypeptides) but not erythrocyte spectrin (αI and βI). Because αII and βII spectrin polypeptides are enriched in axons, we investigated a possible binding of fodaxin to the types of spectrin found in axons. Fodaxin did not bind to isolated brain α chains. Bacterially expressed C-terminal segments 18–19 of βII spectrin bound to fodaxin and inhibited the binding of fodaxin to whole brain spectrin. By contrast, recombinant segments 18–19 of the somatodendritic βIΣ2 spectrin showed no interaction with fodaxin. Within βII, fodaxin binding activity was localized to residues 2,087–2,198, which are unique to βII and link between the end of segment 18 and the pleckstrin homology domain in segment 19. The divergent regions of sequence in segments 19 of βII and βIΣ2 are candidates to mediate the isotype-specific functions of spectrin. Fodaxin is the first protein to be described that discriminates between the unique regions of β spectrin isoforms.     

The Listeria monocytogenesiap gene as an indicator gene for the study of PrfA-dependent regulation

The Bacillus subtilis 168 RecR protein bound to duplex DNA in the presence of ATP and divalent cations (Mg²⁺ and Zn²⁺) was visualized by electron microscopy as a nearly spherical particle. A RecR homomultimer is frequently located at the intersection of two duplex DNA strands in an interwound DNA molecule, generating DNA loops of variable length. Two individual DNA molecules bound to the same protein are seen at a very low frequency, if at all. The association of RecR with the intersection of two duplex DNA strands is more often seen in supercoiled than with relaxed or linear DNA. The RecR protein displays a slight but significant preference for negatively supercoiled over linear DNA. The minimum substrate size for RecR protein is about 150 bp in length. A possible mechanism for RecR function in DNA repair is discussed. Received: 13 August 1996 / Accepted: 18 October 1996     

Increased induction of microspore embryos following manipulation of donor plant environment and culture temperature in corn (Zea mays L.)

Microspore cultures were initiated from the North American sweet corn hybrid, Seneca 60. Donor plants were grown under two environments. One treatment comprised plants that matured completely in the greenhouse (GH) (28°C/23°C: day/night), while in a second treatment donor plants were isolated and divided into two treatment sets: cultured directly at 25°C, or given a heat treatment of 32°C for 10 days.Greenhouse-grown plants produced fewer embryo-like structures (ELS) than growth chambertreated plants regardless of the culture temperature treatment. If the microspores isolated from GC plants were subsequently provided with the initial high culture temperature, the number of ELS that could be recovered was more than doubled compared to the cultures incubated at 25°C continuously. The high culture temperature treatment also resulted in a higher quality of ELS (more compact), which led to a higher frequency of ELS that survived and were subsequently transferred to regeneration medium. However, while plant regeneration and subsequent selfed seeds were obtained, the frequency was very low and further research is required in this area.     

Antisense inhibition of c-myc expression reveals common and distinct mechanisms of growth inhibition by TGF beta and TNF alpha

Downregulation of the c-myc gene in HL-60 cells is associated with growth inhibition and induction of differentiation. Previous studies have reported that the growth inhibitors TGF beta and TNF alpha downregulate c-myc mRNA levels, suggesting the possibility that these agents may exert some of their phenotypic effects via c-myc downregulation. Our study demonstrates that although both growth inhibitors produce a similar decrease in c-myc protein synthesis, TNF alpha produces a greater growth inhibition and differentiation induction in HL-60 cells. Combined addition of anti-myc oligomer with either growth inhibitor produces no additive effect. In fact, 4 microM anti-myc oligomer produces the same growth and differentiation effects as does 10 ng/ml TGF beta 1. We conclude that downregulation of c-myc expression represents a common mechanism of growth inhibition by TGF beta and TNF alpha, but that TNF alpha possesses an additional effect that is independent of c-myc expression.     

HL-60细胞诱导分化与细胞膜流动性变化研究

 本实验以二甲基亚砜(Dimethyl Sulfoxide,DMSO)为诱导剂,诱导人早幼粒白血病细胞系HL-60沿粒系统成熟分化。动态观察了诱导后1—6天HL-60的形态、功能成熟度改变、膜流动性和增殖活性的变化。结果表明,早幼粒细胞由诱导前的78％降至5％,杆核与分叶核细胞由6％和1.5％分别增加至32.5％和5.5％。NBT(Nitroblue tetrazolium,四唑氮蓝)还原试验显示其功能亦渐超成熟。诱导后HL-60 DNA合成速率明显降低(降低40～75％),膜脂流动度亦显著降低(降低30％,P<0.01)。提示诱导分化后的HL-60细胞不仅获得了与正常成熟粒细胞相似的形态功能特征,同时还失去了膜流动性增高及快速繁殖增生的恶性特征。     

1,25-(OH)_2D_3诱导HL-60细胞分化后胞液Ca~(2+)浓度、磷酸化酶a和微粒体Ca~(2+)-ATP酶活性的改变

1,25-(OH)_2D_3对HL-60细胞具有促分化作用。本文报道了1,25-(OH)_2D_3在促进HL-60细胞分化前后胞液Ca~(2+)浓度、磷酸化酶a和微粒体Ca~(2+)-ATP酶活性的改变。结果表明,1,25-(OH)_2D_3加入HL-60细胞培养液后72小时,细胞NBT染色阳性率高于70％,形态向正常分化的细胞转化。同对,胞液Ca~(2+)浓度和微粒体Ca~(2+)-ATP酶活性明显降低,而磷酸化酶a活性显著升高。结果提示,在1,25-(OH)2_D_3作用下,HL-60细胞不仅杀菌功能增强,细胞内胞液Ca~(2+)浓度趋向正常,与钙恒稳有关的酶活性也同样发生改变。即1,25-(OH)_2D_3对HL-60细胞的诱导作用伴有钙恒稳的改变。这些变化与DMSO的作用相同。     

Historic overview of studies on fatty acid-binding proteins

Summary Fatty acid-binding proteins (FABPs) were first identified in the cytosol of rat intestinal mucosa during studies on the regulation of intestinal fatty acid uptake. The subsequent finding of FABP activity in the cytosol of many other tissues initially was believed to reflect a single protein. However, the FABPs are now recognized as products of an ancient gene family comprised of at least 9 structurally related, soluble intracellular members, a number of which exhibit high-affinity binding of long-chain fatty acids. Despite recent insights into regulation and tissue-specific expression suggesting FABPs to subserve diverse roles, their precise biological functions remain to be elucidated.