Plant functional types and ecosystem function in relation to global change

Abstract. Plant functional types (PFTs) bridge the gap between plant physiology and community and ecosystem processes, thus providing a powerful tool in climate change research. We aimed at identifying PFTs within the flora of central-western Argentina, and to explore their possible consequences for ecosystem function. We analyzed 24 vegetative and regenerative traits of the 100 most abundant species along a steep climatic gradient. Based on plant traits and standard multivariate techniques, we identified eight PFTs. Our results confirmed, over a wide range of climatic conditions, the occurrence of broad recurrent patterns of association among plant traits reported for other floras; namely trade-offs between high investment in photosynthesis and growth on the one hand, and preferential allocation to storage and defence on the other. Regenerative traits were only partially coupled with vegetative traits. Using easily-measured plant traits and individual species cover in 63 sites, we predicted main community-ecosystem processes along the regional gradient. We hypothesized likely impacts of global climatic change on PFTs and ecosystems in situ, and analysed their probabilities of migrating in response to changing climatic conditions. Finally, we discuss the advantages and limitations of this kind of approach in predicting changes in plant distribution and in ecosystem processes over the next century.     

On stage single cell identification of rat spermatogenic cells

Summry— The study of spermatogenic cell physiology has been hindered by the absence of unbiased methods of identification of cells upon which single cell techniques are being applied. In this work, we have used histochemical techniques, digital videoimaging, quantification of chromatin-bound DNA probes, and measurements of cell diameter to identify single spermatogenic cells at different periods of development. Our criteria of identification permit the definition of four developmental stages of spermatogenesis on which to perform single cell analyses: spermatogonia B/preleptotene spermatocytes, leptotene/zygotene spermatocytes, pachytene spermatocytes, and round spermatids. The use of voltage-sensitive dyes and Ca²⁺-sensitive dyes does not interfere with the estimations of DNA content. The estimations of DNA content of spermatogenic cells can be performed both with near-UV exciged dyes (H₃₃₃₄₂) and long wavelength-excited dyes (ethidium bromide), allowing the use of a wide range of physiological and immunocytochemical fluorescent probes to study the spermatogenic process.     

Phosphorylation of Raf-1 serine 338-serine 339 is an essential regulatory event for Ras-dependent activation and biological signaling.

Activation of the Raf serine/threonine protein kinases is tightly regulated by multiple phosphorylation events. Phosphorylation of either tyrosine 340 or 341 in the catalytic domain of Raf-1 has been previously shown to induce the ability of the protein kinase to phosphorylate MEK. By using a combination of mitogenic and enzymatic assays, we found that phosphorylation of the adjacent residue, serine 338, and, to a lesser extent, serine 339 is essential for the biological and enzymatic activities of Raf-1. Replacement of S338 with alanine blocked the ability of prenylated Raf-CX to transform Rat-1 fibroblasts. Similarly, the loss of S338-S339 in Raf-1 prevented protein kinase activation in COS-7 cells by either oncogenic Ras[V12] or v-Src. Consistent with phosphorylation of S338-S339, acidic amino acid substitutions of these residues partially restored transforming activity to Raf-CX, as well as kinase activation of Raf-1 by Ras[V12] or v-Src. Two-dimensional phosphopeptide mapping of wild-type Raf-CX and Raf-CX[A338A339] confirmed the presence of a phosphoserine-containing peptide with the predicted mobility in the wild-type protein which was absent from the mutant. This peptide could be quantitatively precipitated by an antipeptide antibody specific for the 18-residue tryptic peptide containing S338-S339 and was demonstrated to contain only phosphoserine. Phosphorylation of this peptide in Raf-1 was significantly increased by coexpression with Ras[V12]. These data demonstrate that Raf-1 residues 338 to 341 constitute a unique phosphoregulatory site in which the phosphorylation of serine and tyrosine residues contributes to the regulation of Raf by Ras, Src, and Ras-independent membrane localization.     

Abdominal Visceral Fat is Associated with a BclI Restriction Fragment Length Polymorphism at the Glucocorticoid Receptor Gene Locus

Several investigations have suggested that body fat distribution is influenced by nonpathologic variations in the responsiveness to Cortisol. Genetic variations in the glucocorticoid receptor (GRL) could therefore potentially have an impact on the level of abdominal fat. A restriction fragment length polymorphism (RFLP) has previously been detected with the BelI restriction enzyme in the GRL gene identifying two alleles with fragment lengths of 4.5 and 2.3 kb. This study investigates whether abdominal fat areas measured by computerized tomography (CT) are associated with this polymorphism in 152 middle-aged men and women. The less frequent 4.5-kb allele was found to be associated with a higher abdominal visceral fat (A VF) area independently of total body fat mass (4.5/4.5 vs. 2.3/2.3 kb genotype; men: 190.7 ± 30.1 vs. 150.7 ± 33.3 cm², p=0.04; women: 132.7 ± 37.3 vs. 101.3 ± 34.5 cm², p=0.06). However, the association with AVF was seen only in subjects of the lower tertile of the percent body fat level. In these subjects, the polymorphism was found to account for 41% (p=0.003) and 35% (p=0.007), in men and women, respectively, of the total variance in AVF area. The consistent association between the GRL polymorphism detected with BelI and AVF area suggests that this gene or a locus in linkage disequilibrium with the BelI restriction site may contribute to the accumulation of AVF.     

Recovery processes after repeated supramaximal exercise at the altitude of 4,350m

Robach, Paul, Daniel Biou, Jean-Pierre Herry, Denis Deberne,Murielle Letournel, Jenny Vaysse, and Jean-Paul Richalet. Recoveryprocesses after repeated supramaximal exercise at the altitude of 4,350 m. J. Appl. Physiol. 82(6):1897-1904, 1997.We tested the hypothesis that prolonged exposureto high altitude would impair the restoration of muscle power duringrepeated sprints. Seven subjects performed two 20-s Wingate tests (WT1and WT2) separated by 5 min of recovery, at sea level (N) and after5-6 days at 4,350 m (H). Mean power output (MPO) andO₂ deficit were measured duringWT. O₂ uptake(O₂) and ventilation(E) were measured continuously. Blood velocity in the femoral artery (FBV) wasrecorded by Doppler ultrasound during recovery. Arterialized blood pHand concentrations of bicarbonate([HCO₃]), venousplasma lactate([La]),norepinephrine ([NE]), and epinephrine ([Epi])were measured before and after WT1 and WT2. MPO decreased between WT1and WT2 by 6.9% in N (P < 0.05) andby 10.7% in H (P < 0.01). H did not further decrease MPO. O₂ deficitdecreased between WT1 and WT2 in H only(P < 0.01). PeakO₂ after WT was reduced by30-40% in H (P < 0.01), butexcess postexercise O₂ consumptionwas not significantly lowered in H. During recovery in H compared with N, E,exercise-induced acidosis, and [NE] were higher,[Epi] tended to be higher,[La] was notaltered, and [HCO₃] andFBV were lower. The similar[La]accumulation was associated with a higher exercise-induced acidosis anda larger increase in [NE] in H. We concluded from thisstudy that prolonged exposure to high altitude did not significantly impair the restoration of muscle power during repeated sprints, despitea limitation of aerobic processes during early recovery.

     

On the role of glucocorticoid receptors in brain plasticity

Summary 1. The mapping of glucocorticoid receptors (GR) in the rat central nervous system (CNS) has demonstrated their widespread presence in large numbers of nerve and glial cell populations also outside the classical stress regions.2. The present paper summarizes the evidence that glucocorticoids via GR in the CNS can act as lifelong organizing signals from development to aging. The following examples are given. (a) In the prepubertal and adult offspring, prenatal corticosterone treatment can produce long-lasting changes in striatal dopaminergic communication. (b) In adulthood, the evidence suggests complex regulation by adrenocortical hormones of neurotrophic factors and their receptors in the hippocampal formation. (c) In aging, the strongly GR-immunoreactive pyramidal cell layer of the CA1 hippocampal area appears to be preferentially vulnerable to neurotoxic actions of glucocorticoids, especially in some rat strains.3. Strong evidence suggests that each nerve cell in the CNS is supported by a trophic unit, consisting of other nerve cells and glial cells, blood vessels, and extracellular matrix molecules. Due to multiple actions on nerve and glial cell populations of the different trophic units, the glucocorticoids may exert either an overall trophic or a neurotoxic action. It seems likely that with increasing age, the endangering actions of glucocorticoids on nerve cells prevail over the neurotrophic ones, leading to reduced nerve cell survival in some trophic units.     

Regeneration and Agrobacterium-mediated transformation of Forsythia×intermedia "Spring Glory"

Internode explants ofin vitro plants ofForsythia x intermedia Spring Glory were transformed with thegus andnpt II genes after inoculation with theA. tumefaciens strain EHA 101 harbouring the plasmid pFAJ3000. Shoot organogenesis took place from callused edges of explants. The first transformed buds were detected 4 to 6 weeks after transfer on regeneration medium, containing 25 mg/l kanamycin as selective agent. An average of 1% of explants regenerated transgenic shoots.-glucuronidase assays and culture on kanamycin-containing medium provided the first indication of integration and expression of introduced genes in transformants. Southern blot and polymerase chain reaction amplification analyses gave molecular confirmation of genetic transformation. Transgenic plants were acclimatized in the greenhouse. Enzymatic assays on several organs of mature plants still showed -glucuronidase activity, thus confirming stable integration of T-DNA in the plant genome.Abbreviations BAP 6-benzyl-aminopurine - CaMV Cauliflower Mosaic Virus - GUS andgus -glucuronidase - IAA indole-3-acetic acid - IBA indole-3-butyric acid - MS Murashige and Skoog - NOS nopaline synthase - NPT II andnpt II neomycin phosphotransferase II - PCR polymerase chain reaction - SDS sodium dodecyl sulphate - SSC sodium chloride-sodium citrate - X-Gluc 5-bromo-4-cbloro-3-indolyl glucuronide     

The mmsA locus of Streptococcus pneumoniae encodes a RecG-like protein involved in DNA repair and in three-strand recombination

We describe the characterization of a mutant strain of Streptococcus pneumoniae previously isolated on the basis of its sensitivity to Methyl Methane Sulphonate (MMS). The mutant strain also exhibited increased sensitivity to UV light and to X-rays, together with a reduced capacity for recombination and Hex-mediated generalized mismatch repair. We show that the original mutant contains two unlinked mutations in the mmsA and in the pms genes. The mmsA wild-type region was cloned and the nucleotide sequence of the mmsA gene was determined. mmsA encodes a polypeptide of 671 amino acids related to a large family of DNA–RNA helicases, with the highest similarity to Escheri-chia coli RecG, a protein involved in the branch migration of Holliday junctions. A plasmid carrying the intact mmsA coding region was shown to restore UV resistance to E. coli recG mutant strains. An mmsA -null mutant constructed by insertion of a chloramphenicol-resistance gene exhibited a 25-fold reduction in recombination during transformation. We suggest that MmsA recognizes and branch migrates three-strand transformation intermediates to extend donor–recipient heteroduplex regions. The mmsA -null mutant exhibited the other phenotypes of the original mutant, apart from mismatch-repair deficiency and, in addition, an alteration in colony-forming ability was noticed. In the pms mutant background, all phenotypes caused by the mmsA mutation were attenuated. Therefore, the pms mutation, although it affected mismatch repair and, to some extent, DNA repair and recombination, acted as a suppressor of the mmsA mutation.     

The Ca2+-sensing receptor: a target for polyamines

The Ca²⁺-sensing receptor(CaR) is activated at physiological levels of externalCa²⁺(Ca_o) but is expressed in anumber of tissues that do not have well-established roles in thecontrol of Ca_o, including several regions of the brain and the intestine. Polyamines are endogenous polyvalent cations that can act as agonists for the CaR, as shown byour current studies of human embryonic kidney (HEK-293) cells transfected with the human CaR. Cellular parameters altered by polyamines included cytosolic freeCa²⁺(Ca_i), inositol phosphateproduction, and the activity of a nonselective cation channel. Sperminestimulated Ca_i transients inCaR-transfected HEK cells, with a concentration producing ahalf-maximal response (EC₅₀) of ~500µM in the presence of 0.5 mMCa²⁺, whereas sustained increasesin Ca_i had anEC₅₀ of ~200 µM. The order ofpotency was spermine > spermidine >> putrescine. Elevation ofCa_o shifted theEC₅₀ for spermine sharply to theleft, with substantial stimulation below 100 µM. Addition ofsubthreshold concentrations of spermine increased the sensitivity ofCaR-expressing HEK cells to Ca_o.Parathyroid hormone secretion from bovine parathyroid cells wasinhibited by 50% in the presence of 200 µM spermine, a responsesimilar to that elicited by 2.0 mMCa_o. These data suggest thatpolyamines could be effective agonists for the CaR, and severaltissues, including the brain, may use the CaR as a target for theactions of spermine and other endogenous polycationic agonists.

     

17 β-Estradiol Enhances the Outgrowth and Survival of Neocortical Neurons in Culture

Results of this investigation demonstrate that exposure to 17 -estradiol differentially and significantly regulates cortical nerve cell outgrowth depending on the cortical region. Parietal and occipital neurons treated with 1 nM 17 -estradiol showed a greater magnitude of neuronal outgrowth whereas outgrowth of temporal cortex neurons was decreased in the presence of 1 nM 17 -estradiol. Frontal cortex neurons showed a consistent enhancement of neuronal outgrowth that did not reach statistical significance. The dose response profile for 17 -estradiol regulation of the macromorphological features exhibited a bimodal dose response relationship whereas the dose response profile for 17 -estradiol regulation of the micromorphological features exhibited a dose response more characteristic of an inverted V-shaped function. An antagonist to the NMDA receptor antagonist, AP5, abolished the growth promoting effect of 17 -estradiol whereas the nuclear estrogen receptor antagonist ICI 182,780 did not. Lastly, neocortical neurons exposed to 17 -estradiol exhibited greater viability and survival than control neurons over a two week period. These data indicate that 17 -estradiol can enhance the growth and viability of select populations of neocortical neurons and that the growth promoting effects of 17 -estradiol can be blocked by an antagonist to the NMDA glutamate receptor and not by an antagonist to the estrogen nuclear receptor.