IRANIAN JOURNAL OF BIOLOGY
Year:2008 | Volume:21 | Issue:2|Papers Count:22

Proteins belong to the RecQ family found in prokaryotes and eukaryotes have a central domain with seven conserved motifs which perform DNA helicase activity. Members of the family in E.coli, yeast and human have been shown to be involved in DNA repair, recombination, transcription and replication. Recently the completion of the whole genome sequence of the model plant Arabidopsis thaliana allowed for identification of seven putative RecQ homologues. We already showed that RecQl4A is involved in plant responses to DNA damage and the regulation of DNA recombination. Here, an evolutionary comparison between the RecQl4A protein and other RecQ family members is shown. In addition, the roles that RecQl4A plays in the repair of DNA damage caused by methyl methanesulfonate MMS in seed germination and seedlings growth are uncovered. A phylogenetic analysis revealed that Arabidopsis RecQl4A and RecQl4B have evolved from a recent duplication but others are more distantly related, suggesting that multiple RecQ genes were present in the last common ancestor of plants and animals. Results obtained from analysis of three independent T-DNA mutants showed recQl4A mutant seedlings are hypersensitive to increasing concentrations of MMS, as compared to wild type. However, no phenotypic differences between the wild type and mutant germinating seeds were observed when seeds grown on medium containing MMS. These suggest that RecQl4A may play various roles in DNA repair in different developmental stages of Arabidopsis growth. Unraveling the exact roles that RecQl4A plays in DNA repair and recombination may allow for developing new tools for gene targeting in plants.

Xanthomonas campestris produces a water- soluble extracellular polysaccharide, xanthan gum, which is extensively applied in food and other industries. This bacterium is not able to utilize lactose due to low levels of b- galactosidase activity or absence of the enzyme. Consequently very little xanthan is produced when the bacterium grows in lactose- based media such as whey. Whey poses a major waste disposal problem due to its high BOD. Therefore, this waste is a suitable substrate for conducting fermentation processes. In this study, a mutant strain was isolated from a plenty of Xanthomonas campestris cells exposed to nitrous acid mutagenesis (NA1). Environmental conditions were optimized and maximum activity of the b-galactosidase enzyme obtained at pH 5.5 and 38oC. Also, the b-galactosidase activity in NA1 cultures was increased 9.5 folds, comparing to that of the wild type cultures (336.1 U vs. 35.4 U). Xanthan gum production by NA1 using whey as carbon source was also studied. By using experimental design (Plackett-Burman) and statistical analysis, among seven parameters tested, we found that whey, as the main substrate, and pH were the first factors affecting gum production. Gum production using significant factors was carried out in a lab-scale fermentor and 10 g l-1 xanthan was obtained.

Phylogenic relationships among the Iranian populations of bisexual Artemia (Nough pool and Urmia Lake samples) were inferred by PCR-RFLP analysis of the mitochondrial 16S rRNA gene with comparison by two reference sample, Artemia Urmiana and Artemia franciscana.  Four different haplotypes of A. franciscana were detected in Nough and nine different haplotypes of A. Urmiana in Urmia by using 10 restriction enzymes. Phylogenic analysis of molecular data showed Iranian populations of bisexual Artemia clustered into two clades including: 1- Nough samples and two haplotypes of Urmia 2- Seven different haplotypes of Urmia. Obtained results also show the ability of the used technique for dividing of different bisexual populations of Artemia in Iran. Our study resolve phylogenic relationship among bisexual samples of Iran and it has been determined that there is considerable differences in nucleotide arrangement, at least in ribosomal fragment, between A. Urmiana and  A. franciscana that similar to same previous studies. 

Jasmonates (Jasmonic acid and its methyl ester, methyl jasmonate) are a new group of plant growth regulator that involve in many morphology andphysiological processes and have role of defense in plants. In this research the effects of methyl jasmonate and ethylene on seed germination and the effect of methyl jasmonate on lipid peroxidation and content of chlorophyll, carotenoids and protein were investigated in canola seedling. Seeds of Brasssica napus L. were sown in plastic pots containing sand, clay and peat in proportion of 1:1:2. After 13 days, seedlings were sprayed with methyl jasmonate (100mM) for 3 days then treated with ethylene (50, 70 ppm) for 40 hours. Control plants were sprayed with distilled water only. Data were analyzed using SPSS and Mstatc and averages were compared by LSD test. The results indicated that methyl jasmonate inhibited seed germination but ethylene induced seed germination. Our results also showed that ethylene neutralized effects of methyl jasmonate on inhibition of seed germination and methyl jasmonate mitigated ethylene-induced lipid peroxidation, revealing that less oxidative damage occurred in this group. Chlorophyll and protein content were significantly decreased under ethylene treatment but methyl jasmonate reverse these effects.Results suggested that methyl jasmonate inhibited seed germination but it improved seedling growth under ethylene treatment.

Cadmium is a non-essential element that negatively affects plant growth and its development. In this study, the effect of an arbuscular mycorrhizal (AM) fungus Glomus intraradices on some growth and physiological traits such as fresh and dry weight of root and shoot, photosynthetic pigments, total sugars, total protein content, lipid peroxidation and oxidative stress in wheat (Triticum aestivum L. cv. Azar2) plants under the toxic levels of cadmium was investigated. The experiment was performed by using two treatments (mycorrhizal and non-mycorrhizal) and four cadmium concentrations (0, 250, 750 and 2500  mM CdCl2). Plants received 40 mL nutrient solution (with half P content) three times a week and also 40 mL test solution (contained cadmium) three times a week, alternatively. Plants were grown in a growth chamber with temperatures ranging from 23 to 270C and a 14/10 light/dark period. Leaves and roots from 60-day-old plants were taken and used for investigation. Arbuscular mycorrhizal fungi had a significant influence on root and shoot fresh and dry weights, where the presence of AM fungus caused a decrease in the negative effect of Cd toxicity. Root length decreased due to an increase in Cd concentration, but there was no corresponding effect on the shoot length. Colonized plants showed less negative effect of Cd on their root length than non-AM plants. Determination of chlorophyll a and b content showed decreased chlorophyll content in both AM and non-AM plants by increasing Cd concentration, but this decrease in the mycorrhizal plants was lower than in non-mycorrhizal plants. By increasing in metal concentration, the content of total sugars and total proteins increased in both shoots and roots of AM plants. The amount of malondealdehyde (MDA) increased in roots and shoots of mycorrhizal and nonmycorrhizal plants under Cd toxicity, indicating lipid peroxidation. Activity of detoxifying enzymes, guaiacol peroxidase (GUPX) and ascorbate peroxidase (APX) in AM and non-AM plants increased but the increase of these activities in mycorrhizal plants was higher than non-mycorrhizal ones. Root length colonization was measured by gridline intersect method. Mycorrhizal colonization decreased due to the Cd exposure significantly. According to these results, it is suggested that this fungus (G. intraradices) can help wheat plants to tolerate Cd toxicity.

Proton gradient – dependent efflux pumps play important role in multidrug resistance (MDR) in Pseudomonas aeruginosa. 23 MDR strains were selected from 104 clinical isolates of P. aeruginosa and screened for resistance to ceftazidim, ceftriaxone, ciprofloxacin, ofloxacin, amikacin, gentamicin and ethidium bromide by determining MICs. The MICs of EtBr and antibiotics were also measured in presence of protonophore, carbonyl cyanide m-chlorophenyl hydrazone (CCCP). Active efflux was assessed using ethidium bromide accumulation assays. Drug accumulation studies for fluoroquinolones were performed to determine the drug specificity of efflux. PCR was used to identify the mexAB-oprM gene in clinical isolates of P. aeruginosa. CCCP reduced the MICs of antibiotics at least in 1 dilution. Ethidium bromide accumulation assays confirmed the presence of proton gradient–dependent efflux mechanism in clinical isolates of P. aeruginosa and accumulation assays of fluoroquinolones showed that efflux systems in this bacterium extrude the structurally and functionally dissimilar antimicrobial agents. PCR demonstrated that 17% of clinical isolates of P. aeruginosa had the mexAB-oprM genes on the chromosome. This study indicates the presence of other RND efflux pumps, in addition to MexAB-OprM in multidrug resistance in clinical isolates of P .aeruginosa.

The measurement of the phytohormone ABA was determined following to study of sensitivity, validity and reproducibility of different techniques. An indirect competitive enzyme-linked immunosorbent assay (ELISA) to the quantitative analysis of ABA in Dunaliella salina was selected. Because of its small size, ABA is not itself immunogenic. Therefore it counts as a Haptenn. The bovine serum albumin (BSA) as a protein carrier can be used for preparation of suitable immunogen. The ABA was coupled to bovine serum albumin. The evaluation of conjugates was determined by UV-spectroscopic analysis. Then the immunizations of rabbits were performed. Immune rabbits were bled after booster injection. The immunoglobulin fraction was isolated from other proteins of serum. In competitive Elisa, free and coated antigens compete for binding sites on the antibody. The second antibody enzyme labeled with peroxidase was added. Bound enzyme activity was calorimetrically determined after addition of substrate (TMB). The standard curve of Elisa was obtained by plotting absorbance at 450 nm versus the log of ABA concentration in the assay. Absorbance was linear between 100 pg and 1000 ng ABA concentration. The evaluation of coefficient of variation (%CV) in inter and intra assay of standard curves were accepted in the range (below 10). When known amounts of ABA were added as internal standard to purified alga extracts, the recovery was evaluated about 109%. This high recovery confirms both the specificity and accuracy of the assay. When the parallelism test was performed in purified alga extracts and in a serial diluted samples, the parallel pattern to the standard curve was observed. The Ka (affinity coefficient) values of antibodies were found to be 0.32×109 L.mol-1. In conclusion, our results showed the accuracy of the Elisa assay for measurement of ABA content of D.salina. Then the ABA contents of algal samples were measured in control (1.5M NaCl) and stressed (3.5M NaCl) Dunaliella cells. Results indicated that ABA was found to be as an endogenous compound and also as a stress hormone in D.salina. In D. salina cells, the ABA content was low and the rate of ABA production was increased when the cells were exposed to 3.5 M NaCl in the medium.

Enterococci are members of the normal gut flora of animals and humans and are released into the environment directly or via sewage outlets. The aim of the study was to detect and analyze the biochemical diversity and antibiotic resistance of the enterococci strains in Tehran sewage. A total of 316 isolates of enterococci were selected on mEnterococcus agar medium and identified at the species level by the common biochemical tests. Antibiotic susceptibility test of isolates with six antibiotics and the MIC was also done using broth macro dilution assay. The results showed that 161, 94, 37, 12, 7, 3, 2 and 1 isolates were E. faecium, E. hirae, E. faecalis, E. gallinarum, E. mundtii, E. raffinosus, E. casseliflavus and E. avium respectively. The antibiotic resistance to the isolates were as follow: 5, 5, 6, 17, 21 and 35% of the isolates were resistant to vancomycin, gentamicin, chloramphenicol, tetracycline, ciprofloxacin and erythromycin respectively. MIC test showed that 15 of the isolates were highly resistant to vancomycin. Although Enterococcal species was considered to have a high distribution in Tehran sewage, but the presence of VRE was limited to E. faecium. Resistance to vancomycin and gentamicin was less than other antibiotics, and resistance to erythromycin and ciprofloxacin was higher.

The objective of the present study was to investigate effective methods in breaking the seed dormancy for two annual medics’ species. Three experiments were conducted to evaluate seed germination of two annual medics including Medicago polymorpha and Medicago rigidula under different prechilling, gibberellic acid and potassium nitrate concentrations and sulfuric acid concentrations in 5 and 10 minutes of applying time. The result showed that all methods broke seed dormancy and exhibited seed germination of annual medics, but some cases were different in species. The most effective and practical method for seed dormancy breaking in M. polymorpha and rigidula was %96 sulfuric acid application for 10 minutes. The main advantages of this method are speed, ease of use, and unaltered physical condition of the seeds following treatment and cheap.

Native plants can be used in creating permanent vegetation and restoration of degraded forests and rangelands in climatic conditions similar to regions as well as initial habitats. Sumac (Rhus coriaria) is native species in vast arid and semi-arid regions of Iran. To investigate vegetative propagation of this plant, a research was conducted using a 2×3 factorial experiment based on RCB (randomized complete block) with replications, in Torogh nursery in Mashhad city Northeast of Iran. treatments included combinations of cutting diameter (Low and High) and media (sand, sand+pit moss and common soil). carried out in Torogh nursery in Mashhad city Northeast of Iran.  Results showed that cutting diameter has no effect on germination, but had a significant effect on survival. Study on soil media showed that soil medium has a significant effect on cuttings germination, but had no significant effect on survival. In addition there was a negative correlation between germination and survival. In this study, the best result was obtained by use of high diameter cuttings in sand.

The abundance of spores and roots colonization by arbuscular mycorrhizal fungi was investigated in the poplar clones planted at the Safrabasteh Poplar Research Station and Kolakavar of Syahkal. The experimental design was a randomized-block with factorial combinations of two sites and four clones as a) Populus euramericana 45.51 b) Populus euramericana I-214 c)Populus deltoids 77.51 and d) Populus deltoids 69/55 in three block. The results showed that most AM spores belong to Glomus mosseae and Glomus intraradices in addition AM spore population and colonization were higher in Safrabasteh than Syahkal. The higher density of AM spore and root colonization found on P.d 77.51 and P.e. 45.51 clones. The interaction effects of poplar clones and site were not significantly on root colonization. This means that AM spore number alone was not as an index for determination of activity and mycorrhizal inoculums potentials and environmental and geographical conditions had important roles for root colonization by AM fungi.

Capparis spinosa L. (Capparidaceae) is one of the few perennial medicinal shrubs, which grows entirely during long summer in the Mediterranean regions. In spite of the increasing worldwide demand for the product of caper crop, little information on the propagation of this plant is available. Caper propagation is usually carried out by seeds and cuttings. However, seed germination performance and rooting of cuttings have serious problems. The objectives of this study were to develop a satisfactory shoot proliferation and rooting procedure on hypocotyl explants for in vitro propagation of caper. The optimum bud formation occurred after 4 weeks on the MS medium supplemented with 0.1 mg/l NAA and 0.5 mg/l BAP. An increase in level of NAA was inhibitory to the formation of shoots. Rooting of the explants on the media containing 0.5 mg/l NAA was the best. Therefore, small regenerated shoots were excised and transferred to root initiation medium. After four weeks roots were observed on the stem bases. The regenerated plantlets were successfully transferred into soil under non-sterile conditions for further development.

The cultivated plants of Tehran city have studied. The results have been summarized as following: The total member of recognized species were 179, the flowering season of 149 species is late spring and early summer. Rosaceae family with 33 species (16.22%) present the most populated family. The most abundant lifeform is Phanerophyte 39.01%. Twenty eight species (%15.64) are native of Iran, from those 16 species are native of Tehran. Among 63 species of ornamental plants (annuals & perennials) were recognized, Compositae family has the biggest family with 17 species.

Salinity stress is one of the important factors that changes the metabolism pathways that effects the synthesis of primary and secondry metabolithes, as allelochemicals. Canola have special allelochemical compounds that are called glucosinolates. Soybean is planted after canola and is sensitive to canola allelochemicals. The aim of this research was to study the allelopathic potential of canola by studying its effect on root and epicotyl growth, chlorophyll a and b amounts and catalase, peroxidase and nitrate reductase activity in soybean seedlings in hydroponic culture. The seeds of canola (Brassica napus L.cv Hyola401) was grown in soils with salinity 0, 6 and 10 dS/m in pots and in 3-5 leaf stage of total plant was extracted. This extraction was added to Hoagland culture contain soybean seedling in %70 cocentration. The results showed with to increasing salinity, allelopathic potential of canola also was increased. The aqueous extract of canola grown in salinity soils decreased chlorophyll a and b amounts in cotyledons, length of root and epicotyl, catalase and peroxidase activity in root and shoot and nitrate reductase activity in cotyledons.