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Background  

Retrotransposons are heterogeneous sequences, widespread in eukaryotic genomes, which refer to the so-called mobile DNA. They resemble retroviruses, both in their structure and for their ability to transpose within the host genome, of which they make up a considerable portion. Copia- and Gypsy-like retrotransposons are the two main classes of retroelements shown to be ubiquitous in plant genomes. Ideally, the retrotransposons life cycle results in the synthesis of a messenger RNA and then self-encoded proteins to process retrotransposon mRNA in double stranded extra-chromosomal cDNA copies which may integrate in new chromosomal locations.  相似文献   

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The sunflower seed (Helianthus annuus L.) major peptidase was purified to molecular homogeneity. It is an 80 kDa enzyme with pI of 4.6 and optimal activity at pH 7.5–8.0 and 45–50°C. It is a thiol-dependent aminopeptidase hydrolyzing peptides in a step-by-step manner as cleaving after the N-terminal amino acid residue of the substrate. It requires substrate acyl parts with a free amino group in either α- or β-position and l-configuration of the adjacent carbon atom. The enzyme prefers amino acid residues with bulky hydrophobic side chains at P1-position and its catalytic efficacy is affected by the structure of both P1 and P1′ parts of the substrate.  相似文献   

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Unlike other oilseeds (e.g. Arabidopsis), developing sunflower seeds do not accumulate a lot of starch and they rely on the sucrose that comes from the mother plant to synthesise lipid precursors. Between 10 and 25 days after flowering (DAF), when sunflower seeds form and complete the main period of storage lipid synthesis, the sucrose content of seeds is relatively constant. By contrast, the glucose and fructose content falls from day 20 after flowering and it is always lower than that of sucrose, with glucose being the minor sugar at the end of the seed formation. By studying the apparent kinetic parameters and the activity of glycolytic enzymes in vitro, it is evident that all the components of the glycolytic pathway are present in the crude seed extract. However, in isolated plastids important enzymatic activities are missing, such as the glyceraldehyde-3-phosphate dehydrogenase, involved in the conversion of glyceraldehyde 3-phosphate into 1,3-biphospho-glycerate, or the enolase that converts 2-phosphoglycerate into phosphoenolpyruvate. Hence, phosphoenolpyruvate or one of its derivatives, like pyruvate and malate from the cytosol, may be the primary carbon sources for lipid biosynthesis. Accordingly, the glucose-6-P imported into the plastid is likely to be used in the pentose phosphate pathway to produce the reducing power for lipid biosynthesis in the form of NADPH. Data from crude seed extracts indicate that enolase activity increased during seed formation, from 16 days after flowering, and that this activity was well correlated with the period of storage lipid synthesis. In addition, while the presence of some glycolytic enzymes increased during lipid synthesis, others decreased, remained constant, or displayed irregular temporal behaviour.  相似文献   

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Chromium (Cr) is a heavy metal risk to human health, and a contaminant found in agricultural soils and industrial sites. Phytoremediation, which relies on phytoextraction of Cr with biological organisms, is an important alternative to costly physical and chemical methods of treating contaminated sites. The ability of the arbuscular mycorrhizal fungus (AM),Glomus intraradices, to enhance Cr uptake and plant tolerance was tested on the growth and gas exchange of sunflower (Helianthus annuus L.). Mycorrhizal-colonized (AM) and non-inoculated (Non-AM) sunflower plants were subjected to two Cr species [trivalent cation (Cr3+) Cr(III) , and divalent dichromate anion (Cr2O7) Cr(VI) ]. Both Cr species depressed plant growth, decreased net photosynthesis (A) and increased the vapor pressure difference; however, Cr(VI) was more toxic. Chromium accumulation was greatest in roots, intermediate in stems and leaves, and lowest in flowers. Greater Cr accumulation occurred with Cr(VI) than Cr(III). AM enhanced the ability of sunflower plants to tolerate and hyperaccumulate Cr. At higher Cr levels greater mycorrhizal dependency occurred, as indicated by proportionally greater growth, higherA and reduced visual symptoms of stress, compared to Non-AM plants. AM plants had greater Cr-accumulating ability than Non-AM plants at the highest concentrations of Cr(III) and Cr(VI), as indicated by the greater Cr phytoextraction coefficient. Mycorrhizal colonization (arbuscule, vesicle, and hyphae formation) was more adversely affected by Cr(VI) than Cr(III), however high levels of colonization still occurred at even the most toxic levels. Arbuscules, which play an important role in mineral ion exchange in root cortical cells, had the greatest sensitivity to Cr toxicity. Higher levels of both Cr species reduced leaf tissue phosphorus (P). While tissue P was higher in AM plants at the highest Cr(III) level, tissue P did not account for mycorrhizal benefits observed with Cr(VI) plants.  相似文献   

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To assess whether foliar application of K+S as potassium sulfate (K2SO4) could alleviate the adverse effects of salt on sunflower (Helianthus annuus L. cv. SF-187) plants, a greenhouse experiment was conducted. There were two NaCl levels (0 and 150 mM) applied to the growth medium and six levels of K+S as K2SO4 (NS (no spray), WS (spray of water+0.1% Tween 20 solution), 0.5% K+0.21% S, 1.0% K+0.41% S, 1.5% K+0.62% S, and 2.0% K+0.82% S in 0.1% Tween-20 solution) applied two times foliarly to non-stressed and salt-stressed sunflower plants. Salt stress markedly repressed the growth, yield, photosynthetic pigments, water relations and photosynthetic attributes, quantum yield (Fv/Fm), leaf and root K+, Mg2+, P, Ca2+, N as well as K+/Na+ ratios, while it enhanced the cell membrane permeability, and leaf and root Na+ and Cl concentrations. Foliar application of potassium sulfate significantly improved growth, achene yield, photosynthetic and transpiration rates, stomatal conductance, water use efficiency, leaf turgor and enhanced shoot and leaf K+ of the salt-stressed sunflower plants, but it did not improve leaf and root Na+, Cl, Mg2+, P, Ca2+, N as well as K+/Na+ ratios. The most effective dose of K+S for improving growth and achene yield was found to be 1.5% K+0.62% S and 1% K+0.41% S, respectively. Improvement in growth of sunflower plants due to exogenously applied K2SO4 was found to be linked to enhanced photosynthetic capacity, water use efficiency, leaf turgor and relative water content.  相似文献   

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The sunflower's wild relative Helianthus annuus L. is a non-native invader in several regions of the world. It was introduced as an experimental forage plant in central Argentina six decades ago where it probably escaped and developed extended populations coexisting with the sunflower crop. If the invasive taxon was diffused without modifications, it would be expected to have phenotypic similarities with its parental sources. Nine populations representative of different geographic regions of central Argentina were compared with 17 populations from the USA (center of origin) in a common garden study at Bahía Blanca, Argentina using 47 phenotypic traits. The nine invasive wild populations were differentiated among themselves and from the native populations by plant form and life cycle traits, oil composition, inflorescence, and achene morphology. Populations from both continents shared traits related to domesticated sunflower, such as bract width over 0.8 cm, but the frequency of this trait was higher in populations from Argentina. The high variability of wild H. annuus populations from Argentina did not reveal any founder effects. The diversity found in the invasive populations reflected about three-fourths of the phenotypic variability of those from the center of origin, even though the environmental conditions of the Argentine habitats represented only half of the variability present in the North American habitats. The current findings demonstrated that the invasive wild sunflower populations have developed within few decades a high degree of variability, which could be a source of a novel biodiversity useful as a genetic resource for sunflower crop improvement.  相似文献   

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Genetic resistance to vesicular-arbuscular (VA) mycorrhiza formation has been obtained in spontaneous or chemically induced mutants of two mycorrhiza-forming species (Pisum sativum L. and Vicia faba L.). The eight mutants, termed myc, are characterized by aborted infections limited to one or two host cells. Expression of the myc character is associated with that of the nod character in both legumes, and is likewise under recessive genetic control. Preliminary analysis of the genetic behaviour of the myc mutants in diallel crosses has shown that at least three genes are involved in VA mycorrhiza infection.  相似文献   

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Trichoderma species are commonly used as biological control agents against phytopathogenic fungi and some strains are able to produce metabolites that enhance plant growth. In the current study we evaluated the production of potential growth-promoting metabolites, rhizosphere competence and endophytism for 101 isolates of Trichoderma from Colombia, and assessed the relationship of these factors to the enhancement of early stages of growth on bean seedlings. Twenty percent of these Trichoderma strains were able to produce soluble forms of phosphate from phosphoric rock. Only 8% of the assessed strains showed consistent ability to produce siderophores to convert ferric iron to soluble forms by chelation. Sixty percent of isolates produced indole-3-acetic acid (IAA) or auxin analogues. The production of any of these metabolites was a characteristic of specific strains, as the ability to produce these metabolites varied greatly within species. Moreover, the production of these substances did not correlate with enhanced growth on bean seedlings, measured as the combined increase in length of roots and aerial parts in the V3 stage of growth. Seven Trichoderma isolates significantly improved the growth of bean seedlings. However, metabolite production varied widely in these seven strains, and some isolates did not produce any of the assessed growth-promoting metabolites. Results indicated that growth was enhanced in the presence of rhizosphere competent and endophytic strains of Trichoderma, and these characteristics were strain-specific and not characteristic for species.  相似文献   

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"Cavitation fatigue" is the increased susceptibility of a xylem conduit to cavitation as a result of its prior cavitation. It was investigated whether cavitation fatigue induced in vivo could be repaired in intact plants. Sunflowers (Helianthus annuus L.) were subjected to soil drought in the greenhouse. Native embolism and vulnerability to cavitation was measured in well-watered controls and after 5 d and 10 d of controlled drought. A dramatic cavitation fatigue was observed where droughted xylem that was refilled in the laboratory developed up to 60 PLC (percentage loss of hydraulic conductivity) at -1 MPa versus only 5.2 PLC in non-droughted controls. Rewatered plants showed the complete reversal of cavitation fatigue over 4 d. Reversal of fatigue was correlated with the refilling of embolized vessels in the intact plants (r(2)=0.91, P<0.01), suggesting that xylem transport to fatigued vessels was required for their repair. The in vivo reversal of fatigue was partially duplicated in excised stem segments by perfusing them with root exudates from droughted (DR) and well-watered (WW) plants. The DR exudate had a greater effect, and this was associated with a greater pH in the DR versus WW saps, but there was no difference in total cation concentration. Perfusions with 2 mM CaCl(2) and KCl solutions also partially reversed cavitation fatigue as opposed to no effect with deionized water, suggesting a role of ions in addition to a pH effect. It is suspected that fatigue is caused by stretching and partial disruption of linkages between cellulose microfibrils in inter-conduit pit membranes during air seeding, and that the reversal of fatigue involves restoring these linkages by ingredients in xylem sap.  相似文献   

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Molecular genetic and morphometric studies of the tall and dwarf forms of the Siberian crabapple, which grow on the territory of Buryatia, were carried out. A phylogenetic analysis based on six highly polymorphic microsatellite loci showed that the dwarf form descends from the tall forms of Malus baccata and both studied forms belong to the same species of Siberian crabapple. Based on the obtained data, we propose that the dwarf form is an ecological form of the Siberian crabapple and possibly represents an initial stage of parapatric speciation.  相似文献   

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Although numerous attempts have been made during the last five decades, no hybrids combining the qualities of the two commercially most important species have been released so far. Dry seeds of Corchorus capsularis L. var. D-154 and Corchorus olitorius L. var. C.G. were irradiated with gamma rays of various intensities from 70 Kr. to 100 Kr. and were sown in the field. Abnormal plants of the first generation showing bilobed and crinkled characters in their leaves induced by gamma rays were chosen as male parents. 300 crosses of different combinations were made. In all 120 fruits developed into maturity. All the seeds failed to germinate except those from the crosses ♀ C.G. (0 Kr.) × ♂ D-154 (80 Kr.) and ♀ D-154 (0 Kr.) × ♂ C.G. (70 Kr.). F1 plants from the cross ♀ C.G. (0 Kr.) × ♂ D-154 (80 Kr.) inherited the bilobed character of the male parent whereas the plants from the other cross failed to show any sign of inheritance of the male parent. This indicated that the plants from the cross ♀ C.G. (0 Kr.) × ♂ D-154 (80 Kr.) were hybrids. These hybrids attained a greater height than the controls and were highly fertile.  相似文献   

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Nodulation and the subsequent nitrogen fixation are important factors that determine the productivity of legumes. The beneficial effects of nodulation can be enhanced when rhizobial inoculation is combined with plant-growth-promoting bacteria (PGPB). The PGPB strain Bacillus thuringiensis-KR1, originally isolated from the nodules of Kudzu vine (Pueraria thunbergiana), was found to promote plant growth of field pea (Pisum sativum L.) and lentil (Lens culinaris L.) under Jensen’s tube, growth pouch and non-sterile soil, respectively, when co-inoculated with Rhizobium leguminosarum-PR1. Coinoculation with B. thuringiensis-KR1 (at a cell density of 106 c.f.u. ml−1) provided the highest and most consistent increase in nodule number, shoot weight, root weight, and total biomass, over rhizobial inoculation alone. The enhancement in nodulation due to coinoculation was 84.6 and 73.3% in pea and lentil respectively compared to R. leguminosarum-PR1 treatment alone. The shoot dry-weight gains on coinoculation with variable cell populations of B. thuringiensis-KR1 varied from 1.04 to 1.15 times and 1.03 to 1.06 times in pea and lentil respectively, while root dry weight ratios of coinoculated treatments varied from 0.98 to 1.14 times and 1.08 to 1.33 times in pea and lentil respectively, those of R. leguminosarum-PR1 inoculated treatment at 42 days of plant growth. While cell densities higher than 106 c.f.u. ml−1 had an inhibitory effect on nodulation and plant growth, lower inoculum levels resulted in decreased cell recovery and plant growth performance. The results of this study indicate the potential of harnessing endophytic bacteria of wild legumes for improving the nodulation and growth of cultivated legumes.  相似文献   

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Treatment of germinating maize seedlings with 0.126 mM of the herbicide Perfluidone (Destun) (1,1,1-trifluoro-4′-[phenylsulfonyl]-methanesulfona-o-toluidide) for 2 days in the dark, then 3 days in the light, at 25°C causes decreases in fresh weight, dry weight, shoot length, and in total chlorophyll and carotenoid contents; in contrast, sunflower seedlings seem not to be affected. Perfluidone causes marked decreases in total lipids and in glyco- and phospholipids of maize seedlings. In sunflower cotyledons, total lipids and pigments (chlorophyll, carotenoids) are not affected, but there is an increase in glycolipids at the expense of phospholipids. After Perfluidone treatment, a significant increase in the fatty acid mole ratio (18∶0+18∶1+18∶2)/18∶3 was found for the maize glycolipids, monogalactosyl diacylglycerol (MGD), digalactosyl diacylglycerol (DGD), and sterol glycoside (SG) + esterified sterol glycoside (ESG), and for the phospholipid, phosphatidylcholine (PC). In sunflower seedlings, however, only the fatty acid mole ratio of ESG + SG showed an increase and that of phosphatidylserine (PS) showed a large decrease. The differential response of the two plant species to Perfluidone suggests that the control of linolenic acid biosynthesis may vary depending on plant species and/or on plant tissues.  相似文献   

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