The relative importance of biological and chemical processes in the release of phosphorus from a highly organic sediment

Bacteria can play an important role in the process of anaerobic phosphorus release: they can act as a direct source of orthophosphates, or as a catalyst of iron hydroxyde reduction. We studied their influence on phosphorus release from highly organic sediments of a Canadian shield lake. Phosphorus and iron release were measured under aerobic and anaerobic conditions, with or without sterilization, and at different pH. We measured also the abundance and activity of bacteria in sediments. The increased P release after sterilization can be explained by cell lysis. Compared to sterilization, changing oxygen concentrations or acidification had little or no effect on P release. In these sediments, phosphorus and iron movements were independent. Most of the total dissolved iron seemed to be linked to humic acids, but not phosphorus.A contribution to the GRIL (Groupe de Recherche Interuniversitaire de Limnologie)     

High prevalence of a point mutation in the porphobilinogen deaminase gene in Dutch patients with acute intermittent porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant disease characterized by a deficiency of porphobilinogen deaminase (PBGD). Up to now 14 different mutations have been described. In an effort to investigate the molecular epidemiology of AIP we have undertaken a systematic study of different exons of the PBGD gene from a large number of unrelated patients. Here, exon 8 from 82 unrelated Dutch and French AIP patients was examined using single strand confirmation polymorphism analysis (SSCP) after polymerase chain reaction (PCR) amplification. A single base mutation, C to T, at position 346 of the sequence coding for PBGD was observed in 15 Dutch families but in only 1 French family. A simple PCR assay is described to facilitate the diagnosis of this common mutation at the DNA level.     

Growth-related gene expression in Nicotiana tabacum mesophyll protoplasts

Eight cDNAs whose genes are more strongly expressed in suspension cells in growth phase than in stationary phase and at a low level in mature leaves have been isolated. The corresponding mRNAs are abundantly accumulated in young plant organs and in germinating seeds but are almost undetectable in mature plant tissues and dry seeds. Six of these cDNAs were characterized by comparison of nucleotide and protein sequences to the EMBL and SWISSPROT databanks. These eight growth-related genes are expressed in protoplasts isolated from Nicotiana tabacum mesophyll cells shortly after preparation (4 h). Two of them are expressed in freshly isolated protoplasts (early genes), while the other six are detected after 4 h of culture (late genes). Seven are more abundantly expressed in protoplasts than in growing plant organs while one growth-related gene is weakly expressed in protoplasts, as is the histone H₄ gene. They seem to be induced in protoplasts by a synergistic effect of wounding and maceration. Sustained expression of the early genes is dependent on the presence of sucrose in the culture medium.     

Production of dissolved organic nitrogen during uptake of nitrate by Synedra planctonica: implications for estimates of new production in the oceans

Nitrate uptake was measured in batch cultures of the unicellularalga Synedra planctonica. During the light period, extensiveexcretion of dissolved organic nitrogen occurred, which representedup to 63% of nitrate uptake between 2 and 4 h into the lightperiod. During the following dark period, most of this excretednitrogen was taken up by dividing cells. New production canbe underestimated by 50% if such a phenomenon occurs duringuptake measurements restricted to the light period.     

Energy cost of walking and gait instability in healthy 65- and 80-yr-olds.

This study tested whether the lower economy of walking in healthy elderly subjects is due to greater gait instability. We compared the energy cost of walking and gait instability (assessed by stride to stride changes in the stride time) in octogenarians (G80, n = 10), 65-yr-olds (G65, n = 10), and young controls (G25, n = 10) walking on a treadmill at six different speeds. The energy cost of walking was higher for G80 than for G25 across the different walking speeds (P < 0.05). Stride time variability at preferred walking speed was significantly greater in G80 (2.31 +/- 0.68%) and G65 (1.93 +/- 0.39%) compared with G25 (1.40 +/- 0.30%; P < 0.05). There was no significant correlation between gait instability and energy cost of walking at preferred walking speed. These findings demonstrated greater energy expenditure in healthy elderly subjects while walking and increased gait instability. However, no relationship was noted between these two variables. The increase in energy cost is probably multifactorial, and our results suggest that gait instability is probably not the main contributing factor in this population. We thus concluded that other mechanisms, such as the energy expenditure associated with walking movements and related to mechanical work, or neuromuscular factors, are more likely involved in the higher cost of walking in elderly people.     

Changes in airway resistance induced by nasal inhalation of cold dry, dry, or moist air in normal individuals

Fontanari, Pierre, Henri Burnet, Marie CarolineZattara-Hartmann, and Yves Jammes. Changes in airway resistanceinduced by nasal inhalation of cold dry, dry, or moist air in normalindividuals. J. Appl. Physiol. 81(4):1739-1743, 1996.Nasopulmonary bronchomotor reflexes elicited bymechanical or irritant stimulation of the nose have been described inanimals and asthmatic patients. However, few studies were devoted tothe consequences of nasal breathing of cold and dry air or of only dryor only moist air on the bronchomotor control in normal individuals.The present study reported changes in interruption resistance (Rint)measured during eupneic breathing of moderately cold (4 or10°C) and dry [0.3% relative humidity (RH)] airor of room air at 23°C that is either dry (0.3% RH) or moist (97%RH). Nasal inhalation of cold (4°C) dry air or of only dryair significantly increased baseline Rint value (17 and 21%,respectively) throughout the 15-min test periods. The response to cold was significantly accentuated when the air temperature was lowered to 10°C (42%). After nasal anesthesia orinhalation of a cholinergic antagonist, cold air did not induce achange in Rint. Nasal inhalation of moist room air had no effect. No Rint changes were measured during oral breathing of the three testagents. It is concluded that the activation of cold receptors orosmoreceptors in the nasal mucosa induces protective bronchoconstrictor responses in normal individuals.

     

Further progress towards a catalogue of all Arabidopsis genes: analysis of a set of 5000 non-redundant ESTs

Nearly 7000 Arabidopsis thaliana -expressed sequence tags (ESTs) from 10 cDNA libraries have been sequenced, of which almost 5000 non-redundant tags have been submitted to the EMBL data bank. The quality of the cDNA libraries used is analysed. Similarity searches in international protein data banks have allowed the detection of significant similarities to a wide range of proteins from many organisms. Alignment with ESTs from the rice systematic sequencing project has allowed the detection of amino acid motifs which are conserved between the two organisms, thus identifying tags to genes encoding highly conserved proteins. These genes are candidates for a common framework in genome mapping projects in different plants.     

Functional analysis of the iron-stress induced CP 43′ polypeptide of PS II in the cyanobacterium Synechococcus sp. PCC 7942

Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43, which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43 apoprotein (designated isiA ^–) and (ii) flavodoxin (designated isiB ^–). The function of CP 43 was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA ^– and isiB ^– strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43 and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crossection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43 is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB ^– strain grown under iron-deficient conditions, CP 43 was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (F_o) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.Abbreviations Chl chlorophyll - CP 43, CP 47 and CP 43 Chl a binding protein complexes of indicated molecular mass - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F_m and F_m fluorescence when all PS II reaction centers are dosed in dark- and light-acclimated cells, respectively - F_o fluorescence when all PS II reaction centers are open in dark acclimated cells - F_v variable fluorescence after dark acclimation (F_m–F_o)     

A novel wound-inducible extensin gene is expressed early in newly isolated protoplasts of Nicotiana sylvestris

A cDNA clone (6PExt 1.2) encoding a novel extensin was isolated from a cDNA library made from 6 h old mesophyll protoplasts of Nicotiana sylvestris. The screening was performed with a heterologous probe from carrot. The encoded polypeptide showed features characteristic of hydroxyproline-rich glycoproteins such as Ser-(Pro)₄ repeats and a high content in Tyr and Lys residues. The presence of four Tyr-X-Tyr-Lys motifs suggests the possibility for intramolecular isodityrosine cross-links whereas three Val-Tyr-Lys motifs may participate in intermolecular cross-links. The analysis of genomic DNA gel blots using both the N. sylvestris and the carrot clones as probes showed that the 6PExt 1.2 gene belongs to a complex multigene family encoding extensin and extensin-related polypeptides in N. sylvestris as well as in related Nicotianeae including a laboratory hybrid. This was confirmed by the analysis of RNA gel blots: a set of mRNAs ranging in size from 0.3 kb to 3.5 kb was found by the carrot extensin probe. The 6PExt 1.2 probe found a 1.2 kb mRNA in protoplasts and in wounded tissues as well as a 0.9 kb mRNA which seemed to be stem-specific. The gene encoding 6PExt 1.2 was induced by wounding in protoplasts, in leaf strips and after Agrobacterium tumefaciens infection of stems.