Changes in the variability of quantitative characters in M2 induced in einkorn wheat by N-nitroso-N-methylurea and X-rays

Changes in the variability of quantitative characters (number of fertile stems, length of the stem and of the spike, number of spikelets in the spike, number of seeds in the spike and in the spikelet) in M₂ induced with 0·1 mM, 0·2 mM and 0·3 mM N-nitroso-N-methylurea (MNH) and with 5000r and 10 000 r of X-rays inTriticum monococcum L. var.sofianum Körn. were evaluated. The mean of the populations remained practically unchanged by the mutagens whereas the variability increased considerably with increasing concentration or dose. Changes in the variability were more pronounced in the values for the first stem than in the values for the first three stems. When changes in the population mean were found (with some of the most elevated concentrations and doses), these changes were shown to be mostly due to a repetition of the cultivation, whereas the changes in the variability were mostly due to the action of the mutagens. In all experimental populations, mutations in quantitative characters were successfully induced.     

Ameliorative effects of <Emphasis Type="Italic">Trichoderma harzianum</Emphasis> on monocot crops under hydroponic saline environment

Ameliorative effects of Trichoderma harzianum (Th-6) on monocot crops under saline environment using hydroponic system were examined. Both rice and maize seeds were coated with T. harzianum (Th-6) and used for the saline and non-saline treatment. Germination and seedling growth performance were studied. T. harzianum (Th-6)-treated seeds showed constantly faster and more uniform germination as compared to untreated seeds. Moreover, seeds treated with Trichoderma improved plants’ growth and physiological performance under hydroponic saline environment compared to control. The treatments showed higher relative water content (RWC), dark-adapted quantum yield (F _v/F _m ratio), performance index (PI_ABS), photochemical quenching (q _P), stomatal conductance (g _s), pigments concentrations and antioxidant enzymes as compared to untreated saline environment. Application of endophyte inhibited the Na⁺ and Cl^? ion uptake in leaves when plants were exposed to saline environment. However, H₂O₂ contents of both treated crops declined under hydroponic salt stress environment. Physiological mechanism of T. harzianum (Th-6) application in mitigating the salt-related consequences of both monocot crops was discussed.     

The effect of deuterium oxide on light-sensitive Paulownia tomentosa seed germination

The effect of deuterium oxide on the germination of light-sensitive Empress tree (Paulownia tomentosa) seeds was studied. Kinetics of germination in both light- and gibberellic acid (GA₃)-induced seeds was decelerated by increasing concentrations of deuterium oxide (D₂O) in the medium. Deuterium oxide in increasing concentrations also changed the duration of the light necessary for germination, from 5 min in H₂O to more than 3 days in 60% D₂O. A far-red (FR) pulse reversed the effect of inductive, prolonged red (R) irradiation; maximum germination could subsequently be restored by only 5 min of red light. The escape from FR reversibility was delayed from 1 day in water to 2 or 3.5 days in D₂O. The light reactions of D₂O-treated seeds resemble those of skotodormant seeds of the same species.     

Interaction between chemical mutagens with a delayed effect and metabolites of seeds

Summary A study was made of the cytogenetic effect of mutagens with a delayed effect (ethylenimine and ethyl methanesulphonate) on Crepis capillaris seeds. The effect was found to depend on the physiological condition of the seeds. In seeds not subjected to prolonged storage, where only chromatid aberrations were occurring spontaneously, mutagens also induced chromatid aberrations only. If, however, because of physiological changes in the seeds (e.g. upon prolonged storage or when seeds were kept at an elevated temperature and humidity) a large number of chromosome-type aberrations appeared, they also appeared when the seeds were acted upon by mutagens with a delayed effect. The action of such mutagens was also found to depend on spontaneous mutation in seeds with different rates of germination. Special experiments showed that the interaction of ethylenimine with the metabolites of seeds in vitro leads to the formation of secondary active mutagens differing from ethylenimine in the nature of their action. The induction of chromosome-type aberrations by treating seeds with alkylating compounds may be due to the action of secondary mutagens.     

Absence of DNA repair replication after chemical mutagen damage in Vicia faba

Exposure of human (Hela) cells to the mutagens 4-nitroquinoline-1-oxide (4NQO) and N-methyl-N′-nitro-nitrosoguanidine (MNNG) produces damage in DNA that is repaired by a mechanism involving the insertion of new bases into DNA (repair replication). Vicia faba root tips, either from soaked seeds containing non-proliferating cells or from growing roots, do not perform detectable amounts of repair replication even though the mutagens inhibit DNA synthesis and cause chromosome aberrations. In view of similar failures to resolve excision in Chlamydomonas, Haplopappus, and Nicotiana after irradiation with UV light and in Vicia faba after X-irradiation it appears that plants in general might lack this repair process.     

Geographical and seasonal variation in water hemlock (Cicuta maculata) toxins

Water hemlock (Cicuta spp.) plants are typically found in wet areas and are toxic to all species of livestock. The toxic components in water hemlock are C₁₇ polyacetylenes, with cicutoxin being the most studied. The objective of this study was to evaluate the variation in cicutoxin and total C₁₇ polyacetylene compounds in water hemlock populations across western North America. Cicutoxin and total C₁₇ polyacetylene concentrations varied among the six collection locations and among plant parts. Tubers contained the highest cicutoxin and total C₁₇ polyacetylene concentrations of all plant parts. Green seeds contained the second most abundant total C₁₇ polyacetylene concentrations. Total C₁₇ polyacetylene and cicutoxin concentrations were also compared in different plant parts at several different phenological stages over the growing season. Cicutoxin and total C₁₇ polyacetylene concentrations in the tubers increased until the green seed stage whereupon the concentrations decreased as the seeds matured and the plant began to senesce. Concentrations of secondary compounds in the stems were consistent with the optimal defense theory in which secondary compounds were higher in stems in earlier development stages compared to later stages and concentrations in seeds were higher than other above ground parts. The toxic compounds are found in all plant parts, with tubers posing the most significant risk of livestock poisoning. Results presented in this study suggest that the toxic risk to livestock likely does not differ between water hemlock (Cicuta maculata) populations across western North America under similar circumstances of ingestion.     

Differential expression of β-conglycinin genes in nodulated and non-nodulated isolines of soybean

Nodulated (T202) and non-nodulated (T201) isolines of soybean (Glycine max [L.] Merr.) were cultivated in a rotated paddy field in Niigata, Japan. The pods, and seeds were harvested at 7-day intervals until maturity, and the subunit compositions of seed storage proteins were analyzed by SDS-PAGE. The β-subunit of β-conglycinin could scarcely be detected in the non-nodulated isoline, T201, at any period throughout seed development, although it was a major component in T202. The accumulation of α′- and α-subunits of β-conglycinin, together with the acidic and basic subunits of glycinin, appeared about one week later in seeds of T201 than in those of T202, perhaps due to a shortage of nitrogen and growth retardation. Northern hybridization could not detect the β-subunit mRNA in immature T201 seeds, while it was pronounced in T202. These results indicate that the suppression of the β-subunit in the non-nodulating isoline T201 is regulated at the level of mRNA accumulation. The α′(α)-subunit mRNAs were actively expressed in both isolines. Total nitrogen concentration was consistently lower in T201 than T202. No significant difference was observed in either the free amino acid or ureide concentrations in seeds, although the concentration of sucrose was considerably lower in T201 seeds and pods compared with T202. This result indicates the possibility that β-subunit accunmlation was regulated not only directly by total nitrogen concentration but also by carbohydrate concentrations. Nitrogen regulation of storage protein subunit levels of soybean seed were evaluated using T201 and T202. Greenhouse-grown plants were subjected to different levels and timing of nitrate treatments. The culture solution (2, 5 or 10 mM NO₃–was supplied from flowering, 42 days after planting (DAP), until maturation (137 DAP), or switched from 2 to 10 mM, or from 10 to 2 mM at 61 DAP. With a continuous 2 mM NO₃–treatment, seed dry weight and N concentration of the T201 plants were significantly lower than those in the T202 plants due to the lack of N₂ fixation by the non nodulated T201 plants. However, when adequate NO₃ was supplied, N concentration and dry weight were similar in T201 and T202 seeds. When 5 mM NO₃ was supplied, the subunit proportion of the seed storage protein was similar in non-nodulating and nodulating isolines. On the other hand, when plants received a low level of NO₃ (2 mM), the β-conglycinin proportion was lower in T201 than in T2O2. Furthermore, in the nodulating T202 plants treated with 10 mM NO₃–the proportion of β-conglycinin increased markedly. The results indicate that non-nodulated T201 has a normal, non-defective, β-subunit gene and that limited N availability decreases accumulation of β-conglycinin, whereas high N availability increases the proportion of β-conglycinin in soybean seeds, irrespective of whether N was derived from N₂ fixation or from NO₃ absorption.     

The fire ephemeral Tersonia cyathiflora (Gyrostemonaceae) germinates in response to smoke but not the butenolide 3-methyl-2H-furo[2,3-c]pyran-2-one

Background and Aims

Tersonia cyathiflora (Gyrostemonaceae) is a fire ephemeral with an obligate requirement for smoke to germinate. Whether it is stimulated to germinate by 3-methyl-2H-furo[2,3-c]pyran-2-one (karrikinolide, KAR₁), the butenolide isolated from smoke that stimulates the germination of many other smoke-responsive species, is tested.

Methods

Seeds of T. cyathiflora were buried in autumn following collection and were exhumed 1 year later, as this alleviates dormancy and enables seeds to germinate in response to smoke-water. Exhumed seeds were tested with smoke-water and KAR₁. Fresh preparations of these solutions were again tested on seeds exhumed 2 months later under a broader range of conditions. They were also tested on Grevillea eriostachya (Proteaceae) and Stylidium affine (Stylidiaceae) to confirm the activity of KAR₁.

Key Results

T. cyathiflora seeds germinated in response to smoke-water but not to KAR₁. In contrast, G. eriostachya and S. affine germinated in response to both smoke-water and KAR₁.

Conclusions

Although many smoke-responsive seeds germinate in the presence of KAR₁, this does not apply universally. This suggests that other chemical(s) in smoke-water may play an important role in stimulating the germination of certain species.     

Exogenous 5-Aminolevulenic Acid Promotes Seed Germination in Elymus nutans against Oxidative Damage Induced by Cold Stress

The protective effects of 5-aminolevulenic acid (ALA) on germination of Elymus nutans Griseb. seeds under cold stress were investigated. Seeds of E. nutans (Damxung, DX and Zhengdao, ZD) were pre-soaked with various concentrations (0, 0.1, 0.5, 1, 5, 10 and 25 mg l⁻¹) of ALA for 24 h before germination under cold stress (5°C). Seeds of ZD were more susceptible to cold stress than DX seeds. Both seeds treated with ALA at low concentrations (0.1–1 mg l⁻¹) had higher final germination percentage (FGP) and dry weight at 5°C than non-ALA-treated seeds, whereas exposure to higher ALA concentrations (5–25 mg l⁻¹) brought about a dose dependent decrease. The highest FGP and dry weight of germinating seeds were obtained from seeds pre-soaked with 1 mg l⁻¹ ALA. After 5 d of cold stress, pretreatment with ALA provided significant protection against cold stress in the germinating seeds, significantly enhancing seed respiration rate and ATP synthesis. ALA pre-treatment also increased reduced glutathione (GSH), ascorbic acid (AsA), total glutathione, and total ascorbate concentrations, and the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), whereas decreased the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), and superoxide radical (O₂ ^•−) release in both germinating seeds under cold stress. In addition, application of ALA increased H⁺-ATPase activity and endogenous ALA concentration compared with cold stress alone. Results indicate that ALA considered as an endogenous plant growth regulator could effectively protect E. nutans seeds from cold-induced oxidative damage during germination without any adverse effect.     

Control of Seed Respiration and Growth in Vicia faba by Oxygen and Temperature: No Evidence for an Oxygen Diffusion Barrier

The rate of dry matter accumulation by seeds of Vicia faba L. cv. Minica increases with temperature in the range of 16 to 26°C. The duration of dry matter accumulation decreases with temperature, resulting in a decrease of final seed dry weight. In this study we test the hypothesis that a diffusion barrier for O₂, located in the seed coat, inhibits seed respiration and growth. The rate of O₂ uptake of intact seeds and of excised embryos and seed coats (separated seeds) was measured in air and buffer at 16, 20, and/or 26°C at various O₂ concentrations and developmental stages. Oxygen uptake rates of intact seeds in buffer were only 9 to 15% of those in air. In buffer, the respiration rate of intact seeds decreased at a pO₂ below air saturation (21 kilopascals), whereas separated seeds showed a decline of O₂ uptake only below 80% of air saturation. In air, embryo excision had no effect on the sensitivity of seed respiration to pO₂, at both 20 and 26°C. In air at 20°C, separated and intact seeds showed similar rates of O₂ uptake. Oxygen uptake by intact seeds, both halfway and beyond the linear growth phase, showed a temperature coefficient Q₁₀ of 2.3 and was insensitive to pO₂ in the range of 80 to 100% of ambient. These results indicate that V. faba seed respiration in air is not limited by the diffusion of O₂ into the seed.     

Effects of gibberellic Acid and gold light on germination, enzyme activities, and amino Acid pool size in a dwarf strain of watermelon

Gibberellic acid (GA₃) promotes and continuous gold light inhibits germination of seeds of a dwarf strain (WB-2) of watermelon [Citrullus lanatus (Thunb.) Matsu. and Nakai]. Osmotic inhibition of germination with mannitol in light-grown seeds of WB-2 was only slightly reversed by GA₃ at the concentrations used, whereas, GA₃ substantially relieved osmotic inhibition in dark-grown seeds.

The effects of GA₃ and gold light on development of catalase and invertase activities and on levels of free amino acids in germinating seeds of WB-2 were examined. Light depressed development of catalase and invertase activity. Levels of free amino acids increased more slowly in embryonic axes of light- than dark-incubated seeds, but in cotyledons higher levels of amino acids were maintained in light-grown seeds. GA₃ accelerated the development of catalase activity in whole embryos and invertase activity in embryonic axes, but did not significantly affect invertase activity in cotyledons during germination. GA₃ had little effect on amino acid pools in cotyledons and embryonic axes.

     

Contamination control of microbe Ziziphus spina [christti] seed in vitro culture

Ziziphus spina [christti] is a naturally distributed tree in subtropical, arid and semi-arid parts of Iran. It is ecologically and economically important due to its tolerance to drought and salinity. Most tree seeds are infected with parasitic and saprophytic microorganisms which decrease the seed germination and seedling establishment. The goal of this paper was to evaluate the ability of selected chemical solutions to inhibit the growth of variety of microbial contaminants in Z. spina [christti] seeds and to enhance the seed germination. Different chemical treatments were used in surface sterilization of seeds: (Treatment 1) sodium hypochlorite (NaOCl) in concentrations of 1, 2 and 4% for 20 min. (Treatment 2) hydrogen peroxide (H₂O₂) in concentration of 4, 8, 12% treated for 10 min. (Treatment 3) 1% mercuric chloride (HgCl₂) at duration 10, 15, 20, 25 min. Seeds were scarified and aseptically, planted on agar Murashige and Skoog (MS) medium. Contaminants were identified according to their morphological and cultural characteristics. Bacterial contaminants included Xanthomonas sp. While Fungal isolates were Fusarium, Penicillium, Alternaria, Rhizopus, and Aspergillus. Our experiment reveals that 4% NaOCl followed by benomyl is the best sterilization treatment for Z. spina [christti] seeds, since the highest number of germination and highest number of sterilized seeds was observed after this treatment.     

Transformation of LTP gene into Brassica napus to enhance its resistance to Sclerotinia sclerotiorum

Rapeseed (Brassica napus L.) is one of the most important economic crops worldwide, and Sclerotinia sclerotiorum is the most dangerous disease that affects its yield greatly. Lipid transfer protein (LTP) has broad-spectrum anti-bacterial and fungal activities. In this study, B. napus was transformed using Agrobacterium tumefaciens harboring the plasmid-containing LTP gene to study its possible capability of increasing plant’s resistance. First, we optimized the petiole genetic transformation system by adjusting the days of explants, bacterial concentrations, ratio of hormones, and cultivating condition. Second, we obtained 8 positive plants by PGR analysis of T0 generation. The PGR results of T₁ generation were positive, indicating that the LTP gene had been integrated into B. napus. Third, T₁ transgenic plants inoculated by detached leaves with mycelia of S. sclerotiorum showed better disease resistance than non-transformants. Oxalic acid belongs to secondary metabolites of S. sclerotiorum, and several studies have demonstrated that the resistance of rapeseed to oxalic acid is significantly consistent with its resistance to S. sclerotiorum. The result from the seed germination assay showed that when T₁ seeds were exposed to oxalic acid stress, their germination rate was evidently higher than that of non-transformant seeds. In addition, we measured some physiological changes in T₁ plants and control plants under oxalic acid stress. The results showed that T₁ transgenic plants had lower malondialdehyde (MDA) content, higher super oxide dismutase (SOD), and peroxidase (POD) activities than non-transformants, whereas disease resistance was related to low MDA content and high SOD and POD activities.     

盐氮处理下盐地碱蓬种子成熟过程中的离子积累和种子萌发特性

研究了盐氮处理条件下盐地碱蓬种子成熟过程中的离子积累以及种子萌发特性,以理解盐地碱蓬在种子发育及萌发过程中对高盐低氮生境的适应性。结果表明,种子成熟过程中,不同浓度盐氮处理下(0.5和5 mmol/L NO₃^--N;1和500 mmol/L NaCl),与果皮和果枝相比, 胚中Na⁺、K⁺、Cl^- 和NO₃^-离子含量几乎没有变化。所有盐氮处理下Na⁺ 和Cl^-都是果皮和果枝中高于胚中,尤其是在高盐处理下。高盐处理下,K⁺ 和NO₃^-含量呈现相反的趋势。高氮时无论高盐还是低盐,果皮中NO₃^-离子含量高于胚中,而果枝中NO₃^-离子含量低于胚中。而低氮时果皮及果枝中NO₃^-离子含量均显著低于胚中。与高氮环境下收获的种子相比,低氮环境下收获的种子萌发率,萌发指数,活力指数都要明显高。上述结果说明,盐地碱蓬种子成熟过程中存在完善的离子调控机制,保护胚免受Na⁺ 和Cl^-等有害离子的伤害并且促进K⁺ 和NO₃^-等营养离子的积累。低NO₃^--N下收获的种子对外界的NO₃^-含量比较敏感,施以较高浓度的NO₃^-能够促进种子萌发,提高萌发指数和活力指数,可能与盐地碱蓬长期适应高盐低氮生境有关。     

Impact of dormancy regulating chemicals on salinity induced dormancy in Lasiurus scindicus and Panicum turgidum: two desert glycophytic grasses

The indigenous forage grasses Lasiurus scindicus and Panicum turgidum are candidate species for the restoration of degraded desert rangelands. The impact of five dormancy regulating chemicals on overcoming salinity-induced germination inhibition was assessed under the best germination conditions in the two species. Seeds were germinated in a series of NaCl concentrations: 0–200 mM NaCl for P. turgidum, and 0–300 mM NaCl for L. scindicus. Lasiurus scindicus seeds were more tolerant to salinity than those of P. turgidum. Twenty percent of P. turgidum seeds germinated in 100 mM NaCl and none in the higher levels, but 47.5% and 8.8% of L. scindicus seeds germinated in 100 and 200 mM NaCl, respectively. The five studied chemicals (fusicoccin, GA₃, kinetin, nitrate and thiourea) did not succeed in improving germination of non-saline treated seeds of the two species, compared to the control, except thiourea in P. turgidum. The salinity-induced germination inhibition in P. turgidum was completely alleviated by the application of gibberellic acid (GA₃), partially alleviated by the application of fusicoccin, kinetin and thiourea, but not affected by nitrate. In L. scindicus, the germination inhibition was completely alleviated by fusicoccin, GA₃, nitrate and thiourea, but partially alleviated by kinetin. For using the two grass species in restoration of degraded rangelands affected by higher salinity, the results suggest using fusicoccin, GA₃, nitrate and thiourea with L. scindicus and GA₃ with P. turgidum seeds as a preseeding treatment can overcome the problem of reduced germination.     

Effects of the inclusion of Moringa oleifera seed on rumen fermentation and methane production in a beef cattle diet using the rumen simulation technique (Rusitec)

Moringa oleifera seeds are currently being used as a livestock feed across tropical regions of the world due to its availability and palatability. However, limited knowledge exists on the effects of the raw seeds on ruminant metabolism. As such, the rumen stimulation technique was used to evaluate the effects of substituting increasing concentrations of ground Moringa seeds (0, 100, 200 and 400 g/kg concentrate dry matter (DM)) in the diet on rumen fermentation and methane production. Two identical, Rusitec apparatuses, each with eight fermenters were used with the first 8 days used for adaptation and days 9 to 16 used for measurements. Fermenters were fed a total mixed ration with Urochloa brizantha as the forage. Disappearance of DM, CP, NDF and ADF linearly decreased (P<0.01) with increasing concentrations of Moringa seeds in the diet. Total volatile fatty acid production and the acetate to propionate ratio were also linearly decreased (P<0.01). However, only the 400 g/kg (concentrate DM basis) treatment differed (P<0.01) from the control. Methane production (%), total microbial incorporation of ¹⁵N and total production of microbial N linearly decreased (P<0.01) as the inclusion of Moringa seeds increased. Though the inclusion of Moringa seeds in the diet decreased CH₄ production, this arose from an unfavourable decrease in diet digestibility and rumen fermentation parameters.     

In vitro seed maturation in Brassica rapa L.: Relationship of silique atmosphere to storage reserve deposition

The Brassica rapa L. silique is a self-contained environment that maintains hypoxia around the developing seeds, and in which carbon dioxide accumulates to very high concentrations (>30,000 ppm). How the silique microenvironment modulates the composition and amount of storage reserves in the seeds is of interest because of the important agricultural role played by canola (B. rapa and Brassica napus) as an oilseed. Because of the small volume and dynamic nature of this microenvironment in Brassica, a standardized system was needed to study the environmental role played in storage reserve deposition. For this purpose we have developed a silique culture system that permits maturation of seed in vitro. Siliques excised from plants just 11 days after pollination complete the ripening of their seeds after 20 days of culture in light (200 μmol/m²/s) on MS medium containing 30 g/l sucrose, 0.25 mg/l BAP, and 0.025 mg/l NAA. Cytochemical localization and biochemical analyses revealed that storage reserves were affected by the in vitro maturation system. Although following a comparable ripening timeline to that occurring on the plant, and producing fully germinable seeds, in vitro maturation resulted in a 40% reduction in seed weight and the mature seeds contained decreased lipid, but increased protein, starch and soluble carbohydrates. To study the internal atmosphere surrounding the seeds, we developed a method to capture silique gases in helium with subsequent quantification of O₂ and CO₂ in the sample by gas chromatography. Analysis of the internal silique atmosphere showed that in vitro siliques provided seeds with a less oxygenated environment than they experience attached to the plant. Carbon dioxide concentrations remained high later into the maturation sequence in vitro than on the plant. When sampling gases from siliques attached to plants, we found multiple samples from the same plant resulted in higher variance than when only a single silique was sampled, suggesting that connection to the plant directly influences internal silique gases. Lower O₂ in the in vitro siliques was correlated with depressed lipid content in their mature seeds, supporting the conclusion that oxygen availability limits lipid accumulation. Previous studies showed how environmental factors influence Brassica embryos grown in tissue culture. These systems fail to preserve the component of metabolic regulation that is enforced by the silique wall tissues. Our in vitro maturation system provides a useful tool for specialized investigations since both the gaseous and hormonal environments can be readily manipulated.     

Leaf gas exchange in species of the Theobroma genus

Species of the Theobroma genus are primarily known by their commercially valuable seeds, especially, T. cacao is one of the most important tropical perennial crops. Beside T. grandiflorum, T. bicolor, and T. angustifolium, T. cacao is the only species of the genus that has been better studied to obtain physiologically relevant information. The main objective of this work was to evaluate the leaf gas exchange in seedlings of seven species of the Theobroma genus, seeking to identify characteristics that could be used in T. cacao breeding programmes. The study was realized under greenhouse conditions using six-month-old seedlings, in which net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration (E), as well as parameters derived from light curves (P _N vs. photosynthetically active radiation) were evaluated. T. cacao, along with T. microcarpum, showed the lowest values of P _N, g _s, and E, while the highest values were presented by T. speciosum, which showed higher saturation irradiance and lower intrinsic and instantaneous water-use efficiencies, being considered the species less conservative in water use. Therefore, the parameters shown by the different evaluated species could serve to design T. cacao genotypes, through introgression of genes for specific environments such as the cabruca system widespread in southern Bahia, Brazil.     

Influence of flanking sequence context on the conformational flexibility of aminofluorene-modified dG adduct in dA mismatch DNA duplexes

When positioned opposite to a dA in a DNA duplex, the prototype arylamine–DNA adduct [N-(2′-deoxyguanosin-yl)-7-fluoro-2-aminofluorene (FAF)] adopts the so-called ‘wedge’ (W) conformation, in which the carcinogen resides in the minor groove of the duplex. All 16 FAF-modified 12-mer NG*N/NAN dA mismatch duplexes (G* = FAF, N = G, A, C, T) exhibited strongly positive induced circular dichroism in the 290–360 nm range (ICD_{290–360 nm}), which supports the W conformation. The ICD_{290–360 nm} intensities were the greatest for duplexes with a 3′-flanking T. The AG*N duplex series showed little adduct-induced destabilization. An exception was the AG*T duplex, which displayed two well-resolved signals in the ¹⁹F NMR spectra. This was presumably due to a strong lesion-destabilizing effect of the 3′-T. The flanking T effect was substantiated further by findings with the TG*T duplex, which exhibited greater lesion flexibility and nucleotide excision repair recognition. Adduct conformational heterogeneity decreased in order of TG*T > AG*T > CG*T > AG*A > AG*G > AG*C. The dramatic flanking T effect on W-conformeric duplexes is consistent with the strong dependence of the ICD_290-360 on both temperature and salt concentration and could be extended to the arylamine food mutagens that are biologically relevant in humans.