Se(IV) phytotoxicity for monocotyledonae cereals (Hordeum vulgare L., Triticum aestivum L.) and dicotyledonae crops (Sinapis alba L., Brassica napus L.)

Significant increases in Donghong kiwifruit yield by a novel umbrella-shaped trellis system and identification of associated molecular mechanisms

China is the largest kiwifruit producer in the world, accounting for more than half of the total. However, in terms of yield per unit area, China is much lower than the global average and lags behind that of other countries. Yield improvement is of critical importance for the current kiwifruit industry in China. In this study, an improved overhead pergolas trellis (OPT) system, namely, the umbrella-shaped trellis (UST) system, was developed for Donghong kiwifruit, which is now the second most popular and widely cultivated red-fleshed kiwifruit in China. Surprisingly, the estimated yield on the UST system was more than two times higher than that with a traditional OPT, while the external fruit quality was maintained and the internal fruit quality was improved. One of the mechanisms contributing to the yield improvement was the significant promotion of the vegetative growth of canes at 6 ~ 10 mm in diameter by the UST system. The upper canopy of the UST treatment served as a natural shading condition for the lower fruiting canopy and thus had positive effects on the accumulation of chlorophylls and total carotenoids in the fruiting canopy. The most productive zones on the fruiting canes (6 ~ 10 mm in diameter) contained significantly higher (P < 0.05) levels of zeatin riboside (ZR) and auxin (IAA) and ratios of ZR/gibberellin (GA), ZR/abscisic acid (ABA), and ABA/GA. A relatively high carbon/nitrogen ratio may promote the flower bud differentiation process of Donghong kiwifruit. The outcomes of this study provide a scientific basis for manifold increase in production of kiwifruit and contribute to the sustainability of the kiwifruit industry.

Effects of interstocks on growth and photosynthetic characteristics in 'Yuanxiaochun' Citrus seedlings

To obtain the compatibility of interstocks crossing with 'Yuanxiaochun', we performed a comparative analysis with five interstocks. From the 60th to 240th day after grafting, there was a significant difference between different treatments. All the new shoot/interstock diameter ratios were <1, indicating that there was no obvious phenomenon of small feet in 'Yuanxiaochun' seedlings of five kinds of interstocks. The density of 'Yuanxiaochun' was significantly different. Chl a, Chl b, T-Chl content of 'Shiranuhi', 'Harumi', 'Tarocco' changed greatly from the 90th to 120th day after grafting. The intercellular CO2 concentration (Ci) of 'Shiranuhi' was significantly higher than the other interstocks. In addition, when 'Yuanxiaochun' was grafted onto 'Shiranuhi', net photosynthetic rate (Pn), stomatal conductance (gs) and tanspiration rate (Tr) were higher. When 'Harumi' were used as the interstocks of 'Yuanxiaochun', the light saturation point (LSP) value was larger, which was conducive to the utilisation of strong light. Moreover, the value of LSP-LCP (LCP, light compensation point) of 'Harumi' and 'Tarocco' were significantly higher than the other three interstocks. The apparent quantum efficiency (AQE), RuBP maximum regeneration rate (Jmax) and maximum carboxylation efficiency of Rubisco (Vcmax) value of 'Shiranuhi' was significantly lower than that of 'Ponkan'. The CO2 compensation point (CCP) of 'Harumi' interstock was lower, but the CO2 saturation point (CSP) of 'Tarocco' interstock was higher than those of other interstocks respectively. There was a small difference in initial fluorescence (F0) of different interstocks. The maximal photochemical efficiency of PSII in the dark (Fv/Fm) of 'Kumquat' was the lowest. In addition, Both Y(II) and ETR values of the 'Yuanxiaochun' leaves of 'Ponkan' interstock was the largest one. However, the non-photochemical quenching (qN) of 'Ponkan' was significantly lower, and that of 'Tarocco' interstock was the highest one. Interstocks have different effect on the growth and development, photosynthetic characteristics related to physiological characteristics of 'Yuanxiaochun' trees. 'Ponkan' and 'Kumquat' as the interstock of 'Yuanxiaochun' was more conducive to the rapid accumulation of photosynthetic products for normal vegetative and reproductive growth of plants.

Phytoremediation of phenol by Hydrilla verticillata (L.f.) Royle and associated effects on physiological parameters

Phenol contamination is a common occurrence in aquatic environments in different parts of the world and strategies that utilize cheap and eco-friendly phytoremediation technologies are required to overcome associated environmental problems. In the present study, the submersed macrophyte Hydrilla verticillata (L.F.) Royle was exposed to different concentrations of phenol (0-200 mg L^-1) to assess its potential in phenol treatment. H. verticillata efficiently degraded phenol in solutions with initial concentrations lower than 200 mg L^-1. The adverse effects of phenol on physiological parameters of H. verticillata were also investigated after 7 d of phenol stress. In order to explore the effect of phenol on the metabolism of H. verticillata during phytoremediation, gas chromatography-mass spectrometry (GC-MS) was used to analyze endogenous soluble organic compounds. The results revealed the presence of greater than 60 soluble organic compounds in H. verticillata. In the process of phenol degradation, fatty acid composition and carbon number distribution were affected in the plants while unsaturated fatty acid content was significantly lower, and several compounds including aliphatic dicarboxylic acids and aromatic ketones were degraded while new compounds were synthesized by the plant. In summary, H. verticillata is a promising candidate for the phytoremediation of the phenol-contaminated aquatic system.

Comparative proteomic analysis of pepper (Capsicum annuum L.) seedlings under selenium stress

Selenium (Se) is an essential trace element for human and animal health. Se fertilizer has been used to increase the Se content in crops to meet the Se requirements in humans and animals. To address the challenge of Se poisoning in plants, the mechanisms underlying Se-induced stress in plants must be understood. Here, to elucidate the effects of Se stress on the protein levels in pepper, we used an integrated approach involving tandem mass tag labeling, high performance liquid chromatography fractionation, and mass spectrometry-based analysis. A total of 4,693 proteins were identified, 3,938 of which yielded quantitative information. Among them, the expression of 172 proteins was up-regulated, and the expression of 28 proteins was down-regulated in the Se/mock treatment comparison. According to the above data, we performed a systematic bioinformatics analysis of all identified proteins and differentially expressed proteins (DEPs). The DEPs were most strongly associated with the terms “metabolic process,” “posttranslational modification, protein turnover, chaperones,” and “protein processing in endoplasmic reticulum” according to Gene Ontology, eukaryotic orthologous groups classification, and Kyoto Encyclopedia of Genes and Genomes enrichment analysis, respectively. Furthermore, several heat shock proteins were identified as DEPs. These results provide insights that may facilitate further studies on the pepper proteome expressed downstream of the Se stress response. Our data revealed that the responses of pepper to Se stress involve various pathways.

Physiological and transcriptome analyses of photosynthesis and chlorophyll metabolism in variegated Citrus (Shiranuhi and Huangguogan) seedlings

Citrus species are among the most economically important fruit crops. Physiological characteristics and molecular mechanisms associated with de-etiolation have been partially revealed. However, little is known about the mechanisms controlling the expression and function of genes associated with photosynthesis and chlorophyll biosynthesis in variegated citrus seedlings. The lower biomass, chlorophyll contents, and photosynthetic parameter values recorded for the variegated seedlings suggested that chlorophyll biosynthesis was partially inhibited. Additionally, roots of the variegated seedlings were longer than the roots of green seedlings. We obtained 567.07 million clean reads and 85.05 Gb of RNA-sequencing data, with more than 94.19% of the reads having a quality score of Q30 (sequencing error rate = 0.1%). Furthermore, we detected 4,786 and 7,007 differentially expressed genes (DEGs) between variegated and green Shiranuhi and Huangguogan seedlings. Thirty common pathways were differentially regulated, including pathways related to photosynthesis (GO: 0015979) and the chloroplast (GO: 0009507). Photosynthesis (44 and 63 DEGs), photosynthesis-antenna proteins (14 and 29 DEGs), and flavonoid biosynthesis (16 and 29 DEGs) pathways were the most common KEGG pathways detected in two analyzed libraries. Differences in the expression patterns of PsbQ, PetF, PetB, PsaA, PsaN, PsbP, PsaF, Cluster-2274.8338 (ZIP1), Cluster-2274.38688 (PTC52), and Cluster-2274.78784 might be responsible for the variegation in citrus seedlings. We completed a physiological- and transcriptome-level comparison of the Shiranuhi and Huangguogan cultivars that differ in terms of seedling variegation. We performed mRNA-seq analyses of variegated and green Shiranuhi and Huangguogan seedlings to explore the genes and regulatory pathways involved in the inhibition of chlorophyll biosynthesis and decreases in Chl a and Chl b contents. The candidate genes described herein should be investigated in greater detail to further characterize variegated citrus seedlings.

Effects of selenate and red Se-nanoparticles on the photosynthetic apparatus of Nicotiana tabacum

Selenium (Se) is a natural trace element, which shifts its action in a relatively narrow concentration range from nutritional role to toxicity. Although it has been well established that in plants chloroplasts are among the primary targets, the mechanism of toxicity on photosynthesis is not well understood. Here, we compared selenate and red-allotrope elemental selenium nanoparticles (red nanoSe) in in vitro tobacco cultures to investigate their effects on the structure and functions of the photosynthetic machinery. Selenate at 10 mg/L concentration retarded plant growth; it also led to a decreased chlorophyll content, accompanied with an increase in the carotenoid-to-chlorophyll ratio. Structural examinations of the photosynthetic machinery, using electron microscopy, small-angle neutron scattering and circular dichroism spectroscopy, revealed significant perturbation in the macro-organization of the pigment-protein complexes and sizeable shrinkage in the repeat distance of granum thylakoid membranes. As shown by chlorophyll a fluorescence transient measurements, these changes in the ultrastructure were associated with a significantly diminished photosystem II activity and a reduced performance of the photosynthetic electron transport, and an enhanced capability of non-photochemical quenching. These changes in the structure and function of the photosynthetic apparatus explain, at least in part, the retarded growth of plantlets in the presence of 10 mg/L selenate. In contrast, red nanoSe, even at 100 mg/L and selenate at 1 mg/L, exerted no negative effect on the growth of plantlets and affected only marginally the thylakoid membrane ultrastructure and the photosynthetic functions.

Petroleum contamination and bioaugmentation in bacterial rhizosphere communities from Avicennia schaueriana

Anthropogenic activity, such as accidental oil spills, are typical sources of urban mangrove pollution that may affect mangrove bacterial communities as well as their mobile genetic elements. To evaluate remediation strategies, we followed over the time the effects of a petroleum hydrocarbon degrading consortium inoculated on mangrove tree Avicennia schaueriana against artificial petroleum contamination in a phytoremediation greenhouse experiment. Interestingly, despite plant protection due to the inoculation, denaturing gradient gel electrophoresis of the bacterial 16S rRNA gene fragments amplified from the total community DNA indicated that the different treatments did not significantly affect the bacterial community composition. However, while the bacterial community was rather stable, pronounced shifts were observed in the abundance of bacteria carrying plasmids. A PCR-Southern blot hybridization analysis indicated an increase in the abundance of IncP-9 catabolic plasmids. Denaturing gradient gel electrophoresis of naphthalene dioxygenase (ndo) genes amplified from cDNA (RNA) indicated the dominance of a specific ndo gene in the inoculated petroleum amendment treatment. The petroleum hydrocarbon degrading consortium characterization indicated the prevalence of bacteria assigned to Pseudomonas spp., Comamonas spp. and Ochrobactrum spp. IncP-9 plasmids were detected for the first time in Comamonas sp. and Ochrobactrum spp., which is a novelty of this study.

Phenotypical, physiological and biochemical analyses provide insight into selenium-induced phytotoxicity in rice plants

The present study investigated the phenotypical, physiological and biochemical changes of rice plants exposed to high selenium (Se) concentrations to gain an insight into Se-induced phytotoxicity. Results showed that exposure of rice plants to excessive Se resulted in growth retardation and biomass reduction in connection with the decreased levels of chlorophyll, carotenoids and soluble proteins. The reduced water status and an associated increase in sugar and proline levels indicated Se-induced osmotic stress in rice plants. Measurements of Se contents in roots, leaf sheaths and leaves revealed that Se was highly accumulated in leaves followed by leaf sheaths and roots. Se also potentiated its toxicity by impairing oxidative metabolism, as evidenced by enhanced accumulation of hydrogen peroxide, superoxide and lipid peroxidation product. Se toxicity also displayed a desynchronized antioxidant system by elevating the level of glutathione and the activities of superoxide dismutase, glutathione-S-transferase and glutathione peroxidase, whereas decreasing the level of ascorbic acid and the activities of catalase, glutathione reductase and dehydroascorbate reductase. Furthermore, Se triggered methylglyoxal toxicity by inhibiting the activities of glyoxalases I and II, particularly at higher concentrations of Se. Collectively, our results suggest that excessive Se caused phytotoxic effects on rice plants by inducing chlorosis, reducing sugar, protein and antioxidant contents, and exacerbating oxidative stress and methylglyoxal toxicity. Accumulation levels of Se, proline and glutathione could be considered as efficient biomarkers to indicate degrees of Se-induced phytotoxicity in rice, and perhaps in other crops.

The endogenous nitric oxide mediates selenium-induced phytotoxicity by promoting ROS generation in Brassica rapa

Selenium (Se) is suggested as an emerging pollutant in agricultural environment because of the increasing anthropogenic release of Se, which in turn results in phytotoxicity. The most common consequence of Se-induced toxicity in plants is oxidative injury, but how Se induces reactive oxygen species (ROS) burst remains unclear. In this work, histofluorescent staining was applied to monitor the dynamics of ROS and nitric oxide (NO) in the root of Brassica rapa under Se(IV) stress. Se(IV)-induced faster accumulation of NO than ROS. Both NO and ROS accumulation were positively correlated with Se(IV)-induced inhibition of root growth. The NO accumulation was nitrate reductase (NR)- and nitric oxide synthase (NOS)-dependent while ROS accumulation was NADPH oxidase-dependent. The removal of NO by NR inhibitor, NOS inhibitor, and NO scavenger could alleviate Se(IV)-induced expression of Br_Rbohs coding for NADPH oxidase and the following ROS accumulation in roots, which further resulted in the amelioration of Se(IV)-induced oxidative injury and growth inhibition. Thus, we proposed that the endogenous NO played a toxic role in B. rapa under Se(IV) stress by triggering ROS burst. Such findings can be used to evaluate the toxic effects of Se contamination on crop plants.

Dual effects of different selenium species on wheat

Wheat (Triticum aestivum) and its derivative products account for a major source of dietary intake of selenium (Se) in humans and animals, because of its essentiality due to its presence in vital enzymes. Se antioxidant role has resulted in the popularity of agronomic biofortification practises in Se deficient areas. Controlling Se uptake, metabolism, translocation and accumulation in plants will be important to decrease healthy risk of toxicity and deficiency and to help selecting adequate methods for biofortification. Selenate and selenite are the two main inorganic Se forms available in soil and in most of the studies are given separately. That study reveals that both Se species behave differently but combined the prevalent pattern is that of selenite; so it is taken up faster and it seems that interferes with selenate uptake and transport. Selenium has dual effects on wheat plants; at low concentrations it acts as growth stimulant whereas at high concentrations it reduces root elongation and biomass production and alters uptake and translocation of several essential nutrients.