Bioaccumulation of 60Co2+ ions in tobacco plants

Tobacco has previously been used in investigations of metals and radionuclide uptake. This study presents determination of bioaccumulation and translocation of 60Co2+ ions in tobacco plants (Nicotiana tabacum L.) grown in Hoagland’s nutrient solution. Cobalt concentration in tobacco plants increased with increasing concentration in nutrient solution. Bioaccumulation from the initial concentration C0 = 0.96 μM Co reached 90% after 7 day cultivation. Only small amounts of Co accumulated in roots, up to 2 - 4 % were removable from roots by washing with 0.1 M CoCl2, indicating that this portion of Co is bound to the root surface in ion-exchangeable form. Tobacco roots retained approximately 2/3 of accumulated cobalt and 1/3 was transported to shoots. Autoradiography revealed that 60Co was preferentially localized in younger leaves. Prolongation of cultivation time did not change the [Co]roots : [Co]shoots ratio significantly. Relationships between growth rate, transpiration rate, uptake and distribution of cobalt in plant tissue are discussed.

Biochar increases tobacco yield by promoting root growth based on a three-year field application

In order to explore the effects of biochar on root system and growth characteristics of flue-tobacco, three years of field experiments were conducted to study the influence of different biochar application levels [600 (T1), 1200 (T2), 1800(T3), 2400 (T4), 3000 (T5) kg/ha] and no fertilizer (CK) on the root physiological indexes and growth index of tobacco. Compared with local conventional fertilization, the application rate of N fertilizer in each treatment (except for control) was reduced by 40% to analyze the effects of different amount of biochar on the physiological indexes of tobacco roots and leaf photosynthesis during flourishing. The results showed that tobacco plants' root development status in the flourishing period was consistent with the photosynthetic physiological indexes, chlorophyll content, and leaf-area coefficient. Compared with the control, the application of biochar could increase the root vigor by 177.8%. Biochar improved the roots, increasing the total root area by 91.35% and the number of root tips by 100.9%. Meanwhile, biochar increased the net photosynthetic rate of tobacco leaves by 77.3% and the total tobacco biomass by 72.5%. Studies have shown that biochar can promote the development of tobacco roots, and then enhance the photosynthesis of leaves, so that tobacco plants can grow healthily, which is conducive to the tobacco production and the cultivation of soil.

Effect of chelating agents on phytoxicity and bioaccumulation of heavy metals in vascular plants

In this work the effect of chelating agents ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA) on phytotoxicity and bioaccumulation of Cd and Co in tobacco plants (Nicotiana tabacum L.) hydroponically grown in diluted Hoagland media (HM) spiked with 109Cd and 60Co was studied. Speciation analysis using a program Visual MINTEQ showed, that the portion of bioavailable ionic Me2+ forms significantly decreased in the presence of EDTA or NTA in 25% HM for account of [Me-EDTA]2- or [Me-NTA]- complexes. We found that the equimolar addition of EDTA or NTA to 50 μmol/dm3 CdCl2 or CoCl2 in HM positively diminished phytotoxicity of Cd or Co on tobacco plants. Bioaccumulation of Cd by tobacco roots during 8 d cultivation was minimally affected in the presence of equimolar concentrations of EDTA or NTA to 10 μmol/dm3 CdCl2 in media. On the contrary, equimolar concentration of EDTA or NTA added into HM caused considerable decrease of Co uptake by tobacco roots. Cadmium showed higher mobility in conductive tissues of tobacco plants than cobalt and the transport ratio in the presence of EDTA or NTA increased 2-times or 3-times in comparison with control experiments (without addition of chelates), respectively. In the case of cobalt this effect was observed in a less extent. Obtained data suggest the possibilities and constraints in the use of chelating agents in phytoextraction technologies in term of phytotoxicity, uptake and translocation of metals in plant tissues.

Effects of Biochar on Root System Development and Leaf Photosynthetic Characteristics of Flue-cured Tobacco by the Three-years Located Experiment

In order to explore the effects of biochar on root system and growth characteristics of flue-tobacco, three years of field experiments were conducted to study the influence of different biochar application levels [600 (T1), 1200 (T2), 1800(T3), 2400 (T4), 3000 (T5) kg/ha] and no fertilizer (CK) on the root physiological indexes and growth index of tobacco. Compared with local conventional fertilization, the application rate of N fertilizer in each treatment (except for control) was reduced by 40% to analyze the effects of different amount of biochar on the physiological indexes of tobacco roots and leaf photosynthesis during flourishing. The results showed that tobacco plants' root development status in the flourishing period was consistent with the photosynthetic physiological indexes, chlorophyll content, and leaf-area coefficient. Compared with the control, the application of biochar could increase the root vigor by 177.8%. Biochar improved the roots, increasing the total root area by 91.35% and the number of root tips by 100.9%. Meanwhile, biochar increased the net photosynthetic rate of tobacco leaves by 77.3% and the total tobacco biomass by 72.5%. Studies have shown that biochar can promote the development of tobacco roots, and then enhance the photosynthesis of leaves, so that tobacco plants can grow healthily, which is conducive to the tobacco production and the cultivation of soil.

Integrated Biocontrol of Tobacco Bacterial Wilt By Antagonistic Bacteria and Marigold

Tobacco bacterial wilt (TBW) is seriously damages the growth of tobacco. There is an urgent need to find a safer and more effective measure to control TBW. In this study, B. amyloliquefaciens ZM9 and marigold powder were applied to the tobacco roots alone or in combination, and the potential inhibition of TBW was assessed. On the other hand, the effects of these treatments on soil physicochemical properties, rhizosphere microbial community and soil metabolites were also evaluated. The results showed that the application of B. amyloliquefaciens ZM9 or marigold powder alone significantly reduced the abundance of R. solanacearum in rhizosphere soil, while the integrated treatment showed the strongest inhibitory effect. Moreover, the integrated treatment can inhibit the secretion of chemoattractants, and affect the change of rhizosphere soil microbial composition. In conclusion, the combination of antagonistic bacteria agent B. amyloliquefaciens ZM9 with marigold powder can enhance the suppression of TBW. Furthermore, B. amyloliquefaciens ZM9 and marigold have synergistic effects on suppressing TBW by regulation soil physicochemical properties, soil metabolites and microbial structure. This study provide a promising strategy for TBW control by integrated applying of B. amyloliquefaciens ZM9 and marigold powder.

Induced expression of rolC for study of its effect on the expression of genes associated with nicotine synthesis in tobacco

Background. Agrobacterium rhizogenes rol genes cause not only hairy root syndrome in plants, but also affect their secondary metabolism. There are cases of increasing of nicotine content in transgenic tobacco roots expressing rolC alone or in combination with other rol genes. In this work, we evaluated the change in the expression of nicotine synthesis genes and their regulators in response to the induction of expression of rolC. Materials and methods. Plant material was represented by three Nicotiana tabacum genotypes: cv. Samsun and two transgenic lines, derived from this cultivar and containing rolC under dexamethasone inducible promoter: A. rhizogenes rolC (Pdex-A4rolC) and N. tabacum rolC (Pdex-trolC) correspondingly. Fluidigm Biomark RT-PCR was used for evaluation of expression of QPT1, QPT2, A622, ODC, ADC, PMT1, PMT2, PMT3, PMT4, MPO1, MPO2, BBL, MATE1, MATE2, ARF6, ERF168, ERF189, A4rolC, NtrolC, and reference gene gapdh. HPLC-MS / MS analysis was used to determine content of nicotine and its derivatives in plant tissues. Results. Expression of PMT genes for the synthesis of the pyrrolidine ring, as well as the genes, controlling enzyme for final stages of nicotine synthesis, was higher in transgenic lines without induction of rolC expression. Regulatory genes were activated by dexamethasone in both transgenic and control lines, indicating the inapplicability of rolC dexamethasone induction for their study. The level of expression of PMT and MPO genes increased over time in transgenic dexamethasone-induced lines. Nicotine content decreased in transgenic dexamethasone-induced plants. Conclusions. The rolC gene does not play a primary role in the regulation of nicotine synthesis genes. The mechanism of regulation of different nicotine biosynthesis genes and TFs varies.

Species-specific assembly of root-associated bacterial microbiota mediated by a combination of plant specialized metabolites

Plant specialized metabolites (PSMs) influence the taxonomic compositions of the root-associated microbiota; however, the underlying molecular mechanisms and evolutionary trajectories remain elusive. Here, we show that the bacterial genus Arthrobacter is predominant in the tobacco endosphere, and that its enrichment is mediated by a combination of two tobacco-specific PSMs, santhopine and nicotine The isolation and whole genome sequencing of a representative set of Arthrobacter strains identified independent genomic features, including but not limited to genes for santhopine and nicotine catabolism, which are associated with the colonization competence of tobacco roots. Taken together, these data suggest that plant species-specific root microbiota assembly is mediated by bacterial catabolism of a cocktail of PSMs synthesized by the host plant.

Effects of the Application of Biochar in Four Typical Agricultural Soils in China

The purpose of this study was to explore the effects of biochar application on soils in the main tobacco-producing areas in China. The study was conducted in four study regions in China, where the same three experimental treatments were set up in each area, including a control (CK), a treatment involving the application of chemical fertilizer (F), and a treatment involving the application of biochar (B). We analyzed the basic physical and chemical properties, microbial diversity, and root system of tobacco plants. The results show that: Biochar increased the soil pH, which was most obvious in the study site in Shaowu City, Fujian Province (FUS), where the soil pH increased by 22.64% and 27.49% compared with soil under the CK and F treatments, respectively. Biochar increased the microbial biomass carbon (MBC) content, and increased the soil content of available nitrogen, phosphorus, and potassium; this effect was most obvious in FUS. The root activity in plots treated with biochar increased by 6.95% and 13.72% compared to the CK and F plots, respectively. Similarly, the number of root tips increased by 89.76% and 21.48% compared to the CK and F plots, respectively. In short, biochar improved the physical soil structure, increased the soil pH, and promoted the effectiveness of soil nutrients. Furthermore, biochar improved the bacterial soil diversity, enriched the population structure of soil bacteria, and promoted the healthy development of flue-cured tobacco roots. However, the demand for and types of biochar suitable for use in different tobacco-planting soils need further study.

Activation of potassium released from soil by root-secreted organic acids in different varieties of tobacco (Nicotiana tabacum)

Organic acids secreted from the roots of plants play important roles in nutrient acquisition and metal detoxification; however, the precise underlying mechanisms of these processes remain poorly understood. In the present study we examined the content of organic acids exuded from roots and the effects of these organic acids on the activation of slowly available potassium (K) at different K levels, including normal K supply and K-deficient conditions. In addition, the study system also comprised a high-K tobacco variety (ND202) and two common ones (K326 and NC89). Our results showed that high-K varieties exhibited significantly higher contents of organic acids in its root exudates and available K in both rhizosphere and non-rhizosphere soils than the other varieties. This research also suggested that a cyclic process in which soil was acidified after being complexed by organic acids was involved in the release of slowly available K, and that this process primarily depended on the soil pH at high organic acids concentrations, but the complexation of organic ligands became dominant at low concentrations. In conclusion, tobacco roots secrete organic acids to increase available K content and improve the utilisation rate of soil K. High-K varieties probably enhance slowly available K activation by secreting relatively high amounts of organic acids, thus leading to more available K in soil for absorption by plants.