Photosynthetic activity of indica rice sister lines with contrasting cold tolerance

Physiology and Molecular Biology of Plants - Incidence of cold during early stages is an obstacle for the growing progress of rice plants. Cold stress has strong negative effects on photosynthetic...     

Isolation and characterization of an exopolysaccharide depolymerase fromPseudomonas marginalis HT041B

An enzyme has been isolated fromPseudomonas marginalis (a pathogen responsible for the spoilage of fruits and vegetables in storage) that degrades the exopolysaccharide (mw>2×10⁶ Da) produced by this organism. The mechanism of degradation has been determined to be a depolymerization that results from glucosidic cleavage. The product of depolymerization is a polysaccharide of ca. 2.5×10⁵ Da. The enzyme has a molecular weight of approximately 28 kDa, a pH optimum of 6.5, pI=9.1, and an apparent K_m of 1.95×10^–7±3.5×10^–8 M. Native and enzyme-treated marginalan supported no or very limited growth of the bacterium respectively.Mention of brand or firm names does not constitute an endorsement by the U.S. Department of Agriculture over others of a similar nature not mentioned.     

The human QARS locus: assignment of the human gene for glutaminyl-tRNA synthetase to chromosome 1q32–42

Summary We have used a cDNA encoding the core region of the human glutaminyl-tRNA synthetase to determine the chromosomal localization of the corresponding gene. Southern blots of restricted DNA from a panel of rodent-human cell lines and in situ chromosome hybridization gave identical results showing that the human gene locus for glutaminyl-tRNA synthetase resides on the distal long arm of chromosome 1. There are now nine mapped aminoacyl-tRNA synthetase genes in the human genome.     

Distinct physiological responses of two rice cultivars subjected to iron toxicity under field conditions

Iron toxicity is recognised as the most widely distributed nutritional disorder in lowland and irrigated rice, derived from the excessive amounts of ferrous ions generated by the reduction of iron oxides in flooded soils. Rice cultivars with variable degrees of tolerance to iron toxicity have been developed, and cultural practices such as water management and fertilisation can be used to reduce its negative impact. However, because of the complex nature of iron toxicity, few physiological data concerning tolerance mechanisms to excess iron in field conditions are available. To analyse the physiological responses of rice to iron excess in field conditions, two rice cultivars with distinct tolerance to iron toxicity [BR‐IRGA 409 (susceptible) and IRGA 420 (tolerant)] were grown in two areas, with a well‐established history of iron toxicity (in Camaquã, RS, Brazil) and without iron toxicity (in Cachoeirinha, RS, Brazil). Plants from the susceptible cultivar grown in the iron‐toxic site showed lower levels of chlorophylls and soluble proteins (together with higher carbonyl levels) indicating photooxidative and oxidative damage. The toxic effects observed were because of the accumulation of high levels of iron and not because of any indirectly induced shoot deficiency of other nutrients. Higher activities of antioxidative enzymes were also observed in leaves of plants from the susceptible cultivar only in the iron‐toxic site, probably as a result of oxidative stress rather than because of specific involvement in a tolerance mechanism. There was no difference between cultivars in iron accumulation in the symplastic and apoplastic space of leaves, with both cultivars accumulating 85–90% of total leaf iron in the symplast. However, susceptible plants accumulated higher levels of iron in low‐molecular‐mass fractions than tolerant plants. The accumulation of iron in the low‐molecular‐mass fraction probably has a direct influence on iron toxicity, and the adaptive strategy of tolerant plants may rely on their capacity to buffer the iron amounts present in the low mass fraction, a new parameter to be considered when evaluating tolerance to iron excess in field‐cultivated rice plants.     

Differential regulation of the two rice ferritin genes (OsFER1 and OsFER2)

Iron is essential to plants. However, when free and in excess, iron can catalyze the formation of oxygen free radicals. Ferritin, a protein capable of storing up to 4500 atoms of iron, can act as an iron buffer inside plant cells. Using a strategy based in amplicon size difference, we were able to analyze the expression profile of the two rice ferritin genes (OsFER1 and OsFER2). Both genes are expressed, although with different regulation and organ distribution. Exposure to copper, Paraquat, SNP and excess iron led to accumulation of ferritin mRNA, remarkably of OsFER2. The iron-induced expression was abolished by treatment with GSH, indicating that the induction observed is dependent of an oxidative step. OsFER2 mRNA levels in rice flag leaves and panicles at different reproductive stages were higher than OsFER1 mRNA levels. No ferritin mRNA was detected in rice seeds. However, imbibition under light led to ferritin expression, which was abolished when seeds were kept in the dark, suggesting a light-regulated induction. Ferritin mRNA accumulation was seen in the dark only when seeds were germinated in the presence of externally supplied iron. We suggest that the primary role of rice ferritins is related to defense against iron-mediated oxidative stress.     

Production of cutinase by Thermomonospora fusca ATCC 27730

Ten strains belonging to various Thermomonospora species were tested for their ability to hydrolyse the insoluble plant polyester cutin. One strain, the thermophile T . fusca ATCC 27730, was found to produce a highly inducible cutinase when grown in broth medium containing purified apple cv. Golden Delicious cutin. Apple pomace, tomato peel, potato suberin and commercial cork were also shown to induce cutinase production. Addition of glucose to the culture medium either at the beginning of fermentation or after 2 days of incubation in the presence of apple cutin led to repression of cutinase production. The cutinase was active against a wide range of cutins, including those isolated from other apple cultivars as well as tomato, cucumber, grapefruit, and green pepper. Cutinase activity in the induced culture supernatant fluids exhibited a half-life of over 60 min at 70 °C and a pH optimum of 11·0. Some potential applications for cutinases are discussed.     

Distribution of alginate gene sequences in the Pseudomonas rRNA homology group I-Azomonas-Azotobacter lineage of superfamily B procaryotes.

Chromosomal DNA from group I Pseudomonas species, Azotobacter vinelandii, Azomonas macrocytogens, Xanthomonas campestris, Serpens flexibilis, and three enteric bacteria was screened for sequences homologous to four Pseudomonas aeruginosa alginate (alg) genes (algA, pmm, algD, and algR1). All the group I Pseudomonas species tested (including alginate producers and nonproducers) contained sequences homologous to all the P. aeruginosa alg genes used as probes, with the exception of P. stutzeri, which lacked algD. Azotobacter vinelandii also contained sequences homologous to all the alg gene probes tested, while Azomonas macrocytogenes DNA showed homology to all but algD. X. campestris contained sequences homologous to pmm and algR1 but not to algA or algD. The helical bacterium S. flexibilis showed homology to the algR1 gene, suggesting that an environmentally responsive regulatory gene similar to algR1 exists in S. flexibilis. Escherichia coli showed homology to the algD and algR1 genes, while Salmonella typhimurium and Klebsiella pneumoniae failed to show homology with any of the P. aeruginosa alg genes. Since all the organisms tested are superfamily B procaryotes, these results suggest that within superfamily B, the alginate genes are distributed throughout the Pseudomonas group I-Azotobacter-Azomonas lineage, while only some alg genes have been retained in the Pseudomonas group V (Xanthomonas) and enteric lineages.     

Exopolysaccharide production by Bifidobacterium longum BB-79

Bifidobacterium longum BB-79 produced an acidic extracellular polysaccharide (EPS), especially when grown on solid medium. The EPS was isolated by ethanol precipitation followed by dialysis and lyophilization. Anion exchange and gel-filtration chromatography were used to further purify and characterize the EPS. The average molecular weight was greater than 200 kDa as estimated by chromatography. Based on gas-liquid chromatography (GLC) and GLC-mass spectrometry analyses, the EPS appears to be composed of galactose and an unidentified hexose (possibly glucose) with a carboxyethyl (lactic acid) substituent. Lactose, when used as the primary carbon source in liquid media, gave the highest yield of EPS. Incubation times longer than 24 h and the initial culture pH (pH 6·0–9·0) had little effect on the amount of EPS produced.     

News & Notes: The Effect of Ethanol and Oxygen on the Growth of Zymomonas mobilis and the Levels of Hopanoids and Other Membrane Lipids

Zymomonas mobilis (ATCC 29191) was grown either aerobically or anaerobically in the presence of 2% (wt/vol) glucose and 0, 3, or 6% (vol/vol) ethanol. The rates of growth and the composition of hopanoids, cellular fatty acids, and other lipids in the bacterial membranes were quantitatively analyzed. The bacterium grew in the presence of 3% and 6% ethanol and was more ethanol tolerant when grown anaerobically. In the absence of ethanol, hopanoids comprised about 30% (by mass) of the total cellular lipids. Addition of ethanol to the media caused complex changes in the levels of hopanoids and other lipids. However, there was not a significant increase in any of the hopanoid lipid classes as ethanol concentration was increased. As previously reported, vaccenic acid was the most abundant fatty acid in the lipids of Z. mobilis, and its high constitutive levels were unaffected by the variations in ethanol and oxygen concentrations. A cyclopropane fatty acid accounted for 2.6–6.4 wt % of the total fatty acids in all treatments. Received: 12 November 1996 / Accepted: 25 February 1997     

Widespread and ancient distribution of a noncanonical genetic code in diplomonads

Recently, a group of diplomonads has been found to use a genetic code in which TAA and TAG encode glutamine rather than termination. To survey the distribution of this characteristic in diplomonads, we sought to identify TAA and TAG codons at positions where glutamine is expected in genes for alpha-tubulin, elongation factor-1 alpha, and the gamma subunit of eukaryotic translation initiation factor-2. These sequences show that the variant genetic code is utilized by almost all diplomonads, with the genus Giardia alone using the universal genetic code. Comparative phylogenetic analysis reveals that the switch to this genetic code took place very early in the evolution of diplomonads and was likely a single event. Termination signals and downstream untranslated regions were also cloned from three Hexamita genes. In all three of these genes, the predicted TGA termination codon was found at the expected position. Interestingly, the untranslated regions of these genes are high in AT. This is incongruent with the coding regions, which are comparatively GC-rich.