Adaptation to salt stress in a salt-tolerant strain of the yeast Yarrowia lipolytica.
We have studied the cellular mechanisms underlying adaptation to salt stress in a newly isolated osmo- and salt-tolerant strain of the yeast Yarrowia lipolytica. When cells are incubated in the presence of 9% NaCl, a rapid change in their size and shape is observed. Salt stress is accompanied by an increase in the intracellular level of glycerol, free amino acids (notably proline and aliphatic amino acids), and Na+, as well as by changes in lipid and fatty acid composition. (+info)
Isolating the promoter of a stress-induced gene encoding betaine aldehyde dehydrogenase from the halophyte Atriplex centralasiatica Iljin.
The betaine aldehyde dehydrogenase (AcBADH) gene of the halophyte Atriplex centralasiatica Iljin is induced by drought, salinity, cold stress and abscisic acid, in parallel with an increase in betaine level. In order to study the molecular basis of its expression and to obtain an effective stress-induced promoter, the 5' flanking region of betaine aldehyde dehydrogenase gene (about 1.2 kb) was isolated from the halophyte A. centralasiatica Iljin by screening the genomic library. The transcription start site, which localized at 84 bases upstream of the start ATG, was determined by primer extension and 5'-RACE method. To investigate the molecular mechanism of the stress-induced gene regulation, the AcBADH promoter-beta-glucuronidase chimeric gene constructs containing six deletions were introduced into tobacco by Agrobacterium-mediated transformation. The AcBADH 5'-flanking region, a promoter strongly induced by salt stress, contains two salt-responsive enhancer regions localized between -1115 and -890, -462 and -230 and one silencer region between -890 and -641. (+info)
Bacillus patagoniensis sp. nov., a novel alkalitolerant bacterium from the rhizosphere of Atriplex lampa in Patagonia, Argentina.
A Gram-positive, rod-shaped, spore-forming bacterium (PAT 05T) was isolated from the rhizosphere of the perennial shrub Atriplex lampa in north-eastern Patagonia, Argentina. Its overall biochemical and physiological characteristics indicated that this strain should be placed in the alkaliphilic Bacillus group. Strain PAT 05T grew at pH 7-10 (optimum pH 8), but not at pH 6. Its DNA G+C content was 39.7 mol%. Sequence analysis of the 16S rRNA gene of PAT 05T revealed the closest match (99.6 % similarity) with Bacillus sp. DSM 8714. The highest level of DNA-DNA relatedness (88.6 %) was also found with this strain. On the basis of 16S rRNA gene sequence similarity and phylogenetic analysis, G+C content and DNA-DNA hybridization data, strain PAT 05T is related at the species level to Bacillus sp. DSM 8714, a member of a group referred as phenon 4a by Nielsen et al. [Nielsen, P., Fritze, D. & Priest, F. G. (1995). Microbiology 141, 1745-1761], which still lacks taxonomic standing. These results support the proposal of strain PAT 05T (=DSM 16117T=ATCC BAA-965T) as the type strain of Bacillus patagoniensis sp. nov. (+info)
Genetic structure of Atriplex halimus populations in the Mediterranean Basin.
BACKGROUND AND AIMS: The saltbush Atriplex halimus is a chenopodiaceous plant well adapted to dry saline habitats and widely distributed in the Mediterranean Basin. A study was carried out to analyse the genetic diversity of A. halimus at the level of the Mediterranean Basin. METHODS: To assess the intra- and interpopulational variation of A. halimus a total of 51 populations and six plants per populations was analysed with the RAPD-PCR technique. For the study of the phylogeny of the populations, 21 samples of A. halimus and seven samples of other species of Atriplex were analysed by the sequencing of the ITS (internal transcribed spacer) region of the ribosomal DNA. KEY RESULTS: The AMOVA analysis of the RAPD results showed that populations were divided into two discrete genetic groups, as the variation among groups accounted for 54.36 % of the total variance of the collection. At the same time, the intrapopulational diversity was high, as 301 out of 306 plants analysed constituted an individual RAPD haplotype. The sequencing of the ITS region also showed a significant separation of the two genetic groups, with a genetic distance of 0.023 nucleotide substitutions per site. Using A. breweri, A. canescens, A. glauca and A. prostrata as outgroups in the phylogenetic analysis, A. breweri and A. canescens are the species closest to A. halimus from this group, while A. prostrata is the most distant. CONCLUSIONS: The present work indicates that two genetic groups of A. halimus can be distinguished after analysing the genetic diversity of 51 populations from ten countries in the Mediterranean Basin. (+info)
NaCl alleviates polyethylene glycol-induced water stress in the halophyte species Atriplex halimus L.
Atriplex halimus L. is a C4 xero-halophyte species well adapted to salt and drought conditions. To collect information on the physiological impact of low salt levels on their water-stress resistance, seedlings were exposed for 6 d to nutrient solution containing either 0% or 15% polyethylene glycol 10,000 (PEG), in the presence or in the absence of 50 mM NaCl. Similar experiments were performed with one PEG-resistant and one PEG-sensitive selected cell line exposed for 50 d to 0% or 15% PEG on standard Linsmaier and Skoog (LS) medium, on LS medium supplemented with 50 mM NaCl, or on Na+-free medium. NaCl mitigated the deleterious impact of PEG on growth of both whole plants and PEG-sensitive cell lines and improved the ability of stressed tissues to perform osmotic adjustment (OA). Water stress reduced CO2 net assimilation rates quantified in the presence of high CO2 and low O2 levels (A), stomatal conductance and transpiration, but NaCl improved water use efficiency of PEG-treated plants through its positive effect on A values, especially in young leaves. PEG increased the internal Na+ concentration. The resistant cell line accumulated higher concentration of Na+ than the PEG-sensitive one. The complete absence of Na+ in the medium endangered the survival of both cell lines exposed to PEG. Although Na+ by itself contributed only for a small part to OA, NaCl induced an increase in proline concentration and stimulated the synthesis of glycinebetaine in response to PEG in photosynthetic tissues. Soluble sugars were the main contributors to OA and increased when tissues were simultaneously exposed to PEG and NaCl compared with PEG alone, suggesting that Na+ may influence sugar synthesis and/or translocation. (+info)
Growth and photosynthetic responses to salinity of the salt-marsh shrub Atriplex portulacoides.
BACKGROUND AND AIMS: Atriplex (Halimione) portulacoides is a halophytic, C(3) shrub. It is virtually confined to coastal salt marshes, where it often dominates the vegetation. The aim of this study was to investigate its growth responses to salinity and the extent to which these could be explained by photosynthetic physiology. METHODS: The responses of young plants to salinity in the range 0-700 mol m(-3) NaCl were investigated in a glasshouse experiment. The performance of plants was examined using classical growth analysis, measurements of gas exchange (infrared gas analysis), determination of chlorophyll fluorescence characteristics (modulated fluorimeter) and photosynthetic pigment concentrations; total ash, sodium, potassium and nitrogen concentrations, and relative water content were also determined. KEY RESULTS: Plants accumulated Na(+) approximately in proportion to external salinity. Salt stimulated growth up to an external concentration of 200 mol m(-3) NaCl and some growth was maintained at higher salinities. The main determinant of growth response to salinity was unit leaf rate. This was itself reflected in rates of CO(2) assimilation, which were not affected by 200 mol m(-3) but were reduced at higher salinities. Reductions in net photosynthetic rate could be accounted for largely by lower stomatal conductance and intercellular CO(2) concentration. Apart from possible effects of osmotic shock at the beginning of the experiment, salinity did not have any adverse effect on photosystem II (PSII). Neither the quantum efficiency of PSII (Phi(PSII)) nor the chlorophyll fluorescence ratio (F(v)/F(m)) were reduced by salinity, and lower mid-day values recovered by dawn. Mid-day F(v)/F(m) was in fact depressed more at low external sodium concentration, by the end of the experiment. CONCLUSIONS: The growth responses of the hygro-halophyte A. portulacoides to salinity appear largely to depend on changes in its rate of photosynthetic gas exchange. Photosynthesis appears to be limited mainly through stomatal conductance and hence intercellular CO(2) concentration, rather than by effects on PSII; moderate salinity might stimulate carboxylation capacity. This is in contrast to more extreme halophytes, for which an ability to maintain leaf area can partially offset declining rates of carbon assimilation at high salinity. (+info)
An inland and a coastal population of the Mediterranean xero-halophyte species Atriplex halimus L. differ in their ability to accumulate proline and glycinebetaine in response to salinity and water stress.