Effects of silicon on aluminum toxicity in upland rice plants

Aims

This study aimed to determine the capacity of Si to mitigate Al toxicity in upland rice plants (Oryza sativa L.) by evaluating plant growth and the Si and Al uptake kinetics.

Methods

Plants were grown for 40 days, after which the Si and Al uptake kinetics (Cmin, Km and Imax) were analyzed. Then, the shoots and roots were separated, and the dry matter, root morphology and Si and Al concentration and accumulation in the plant were evaluated.

Results

Aluminum decreased plant growth and the Si uptake capacity by decreasing the root growth and Si transport system efficiency in the upland rice roots (> Km and > Cmin). Silicon mitigated Al toxicity in the upland rice plants by decreasing Al transport to the plant shoots, although it did not reduce the Al uptake rate (Imax). Si treatment increased the growth of upland rice plant shoots grown in the presence of Al without influencing the root growth. The alleviation of Al toxicity by Si is more evident in the susceptible upland rice cultivar Maravilha.

Conclusions

Silicon mitigated Al toxicity in the upland rice plants by decreasing Al transport to the plant shoots but did not reduce the Al uptake rate by roots.

     

The miRNAome of ramie (<Emphasis Type="Italic">Boehmeria nivea</Emphasis> L.): identification,expression, and potential roles of novel microRNAs in regulation of cadmium stress response

Background

MicroRNAs (miRNAs) regulate numerous crucial abiotic stress processes in plants. However, information is limited on their involvement in cadmium (Cd) stress response and tolerance mechanisms in plants, including ramie (Boehmeria nivea L.) that produces a number of economic valuable as an important natural fibre crop and an ideal crop for Cd pollution remediation.

Results

Four small RNA libraries of Cd-stressed and non-stressed leaves and roots of ramie were constructed. Using small RNA-sequencing, 73 novel miRNAs were identified. Genome-wide expression analysis revealed that a set of miRNAs was differentially regulated in response to Cd stress. In silico target prediction identified 426 potential miRNA targets that include several uptake or transport factors for heavy metal ions. The reliability of small RNA sequencing and the relationship between the expression levels of miRNAs and their target genes were confirmed by quantitative PCR (q-PCR). We showed that the expression patterns of miRNAs obtained by q-PCR were consistent with those obtained from small RNA sequencing. Moreover, we demonstrated that the expression of six randomly selected target genes was inversely related to that of their corresponding miRNAs, indicating that the miRNAs regulate Cd stress response in ramie.

Conclusions

This study enriches the number of Cd-responsive miRNAs and lays a foundation for the elucidation of the miRNA-mediated regulatory mechanism in ramie during Cd stress.

     

Short-term partitioning of Cd recently taken up between sunflowers organs (<Emphasis Type="Italic">Helianthus annuus</Emphasis>) at flowering and grain filling stages: effect of plant transpiration and allometry

Aims

This work concentrated on understanding the allocation of Cd recently taken up between the organs of sunflower at early and middle reproductive growth stages. The roles of transpiration and allometry were investigated.

Methods

Sunflowers were grown hydroponically in greenhouse, being exposed to low concentrations of Cd (pCd²⁺ = 11.03). At flower bud and grain filling stages, plants were exposed for three days to ¹¹¹Cd and at the same time, subjected or not to fans to increase the transpiration. The partitioning of ¹¹¹Cd between plant organs measured by high resolution ICP-MS was then modelled.

Results

Although the use of fans increased the plant water uptake and transpiration by about 20%, there were no significant effects on the partitioning of recent Cd. Most of the recent Cd was recovered in roots (60%) and only 2.8% were found in seeds (0.8% for the husk and 2.0% for the almonds). The sequestration of recent Cd in a plant organ was successfully explained by its biomass and except for leaves, by the biomass of other organs acting as competitive sinks.

Conclusions

This work proposes a modelling approach for the partitioning of the labelled Cd between plant organs in sunflower.

     

Plant growth-promoting bacterium <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> FR1 secrets a novel type of extracellular polyhydroxybutyrate polymerase involved in abiotic stress response in plants

Objectives

Identification of novel microbial factors contributing to plant protection against abiotic stress.

Results

The genome of plant growth-promoting bacterium Pseudomonas fluorescens FR1 contains a short mobile element encoding a novel type of extracellular polyhydroxybutyrate (PHB) polymerase (PhbC) associated with a type I secretion system. Genetic analysis using a phbC mutant strain and plants showed that this novel extracellular enzyme is related to the PHB production in planta and suggests that PHB could be a beneficial microbial compound synthesized during plant adaptation to cold stress.

Conclusion

Extracellular PhbC can be used as a new tool for improve crop production under abiotic stress.

     

Rapid decrease of soil carbon after abandonment of subtropical paddy fields

Aims

This study is aimed to investigate the efficiency of plant growth-promoting (PGP) strategies of Enterobacter sp. strain EG16 under metal stress and its potential application in phytoremediation.

Methods

Production of siderophores and indole-3-acetic acid (IAA) by EG16 were assessed in a hydroponic system in which Hibiscus cannabinus was grown with different concentrations of Cd and Fe. A pot experiment was also carried out to evaluate the practical effect of EG16 on H. cannabinus growth and remediation efficiency.

Results

Inoculation with EG16 significantly improved plant growth, probably as a result of increased plant uptake of Fe and immobilization of Cd²⁺, which resulted in decreased plant accumulation of Cd. Increased production of siderophores by EG16 in response to Cd exposure appeared to be the PGP strategy functioning in the EG16–H. cannabinus association. The bacterial Cd response system promoted plant and bacterial uptake of Fe, alleviated Cd-induced inhibition of bacterial IAA production, and potentially assisted in metal immobilization in the rhizosphere.

Conclusions

The EG16–H. cannabinus association may be useful for phytostabilization, as it exhibits good plant growth, low plant accumulation of metals, and reduced metal bioavailability in soil.

     

A quantitative analysis of root distortion from contrasting wheat cropping systems

Aims

Bacterial ACC deaminase is one of the key tools to ameliorate plant stress by lowering ethylene level in plants. The effects of ACC deaminase-producing bacteria on the volatile profiles in plants have not been examined to date. To address this, we performed metabolic profiling of volatiles in carrots following inoculation of the bacteria producing ACC deaminase.

Methods

We isolated ACC deaminase-producing bacteria from the inner part of the fruits and vegetables grown on organic farms by culturing on ACC-containing media, and screened them with PCR for the acdS gene, mungbean growth assay, and in vitro ACC deaminase activity. The isolated endophytes were evaluated for their ability to alter volatile profiles in carrots.

Results

Eleven bacterial strains possessing the activity to cleave ACC were selected among the 60 isolates grown on the medium containing ACC as a sole N source. Three of them that belonged to Pseudomonas could reduce the levels of (E)-2-hexenal and the other green leaf volatiles (GLVs) and terpenoids in the carrot leaves following inoculation of the seeds.

Conclusions

The isolated endophytes with ACC deaminase activity could alter the composition of volatiles in plants, probably through lowering ethylene level in the plant.

     

High-mass-resolution MALDI mass spectrometry imaging reveals detailed spatial distribution of metabolites and lipids in roots of barley seedlings in response to salinity stress

Introduction

Mass spectrometry imaging (MSI) is a technology that enables the visualization of the spatial distribution of hundreds to thousands of metabolites in the same tissue section simultaneously. Roots are below-ground plant organs that anchor plants to the soil, take up water and nutrients, and sense and respond to external stresses. Physiological responses to salinity are multifaceted and have predominantly been studied using whole plant tissues that cannot resolve plant salinity responses spatially.

Objectives

This study aimed to use a comprehensive approach to study the spatial distribution and profiles of metabolites, and to quantify the changes in the elemental content in young developing barley seminal roots before and after salinity stress.

Methods

Here, we used a combination of liquid chromatography–mass spectrometry (LC–MS), inductively coupled plasma mass spectrometry (ICP–MS), and matrix-assisted laser desorption/ionization (MALDI–MSI) platforms to profile and analyze the spatial distribution of ions, metabolites and lipids across three anatomically different barley root zones before and after a short-term salinity stress (150 mM NaCl).

Results

We localized, visualized and discriminated compounds in fine detail along longitudinal root sections and compared ion, metabolite, and lipid composition before and after salt stress. Large changes in the phosphatidylcholine (PC) profiles were observed as a response to salt stress with PC 34:n showing an overall reduction in salt treated roots. ICP–MS analysis quantified changes in the elemental content of roots with increases of Na⁺ and decreases of K⁺ content.

Conclusion

Our results established the suitability of combining three mass spectrometry platforms to analyze and map ionic and metabolic responses to salinity stress in plant roots and to elucidate tolerance mechanisms in response to abiotic stress, such as salinity stress.

     

Crop metabolomics: from diagnostics to assisted breeding

Background

Until recently, plant metabolomics have provided a deep understanding on the metabolic regulation in individual plants as experimental units. The application of these techniques to agricultural systems subjected to more complex interactions is a step towards the implementation of translational metabolomics in crop breeding.

Aim of Review

We present here a review paper discussing advances in the knowledge reached in the last years derived from the application of metabolomic techniques that evolved from biomarker discovery to improve crop yield and quality.

Key Scientific Concepts of Review

Translational metabolomics applied to crop breeding programs.

     

Global proteomic mapping of alkali stress regulated molecular networks in <Emphasis Type="Italic">Helianthus tuberosus</Emphasis> L.

Background and aims

Soil salinization with high pH condition is a major abiotic stress to plant growth and crop productivity. Helianthus tuberosus L. is an important stress tolerant plant and can survive in the saline-alkali soil and semiarid areas. The aim of this study is to identify the effect of alkali stress on H. tuberosus through global proteomics analysis and improve understanding of the alkalinity resistance of plants.

Methods

H. tuberosus seedlings were exposed to different level alkali stress for 7 days. Protein profiling was quantified by conducting MS-based comparative proteomics analysis. RT-PCR study was carried out to analyze the mRNA expression levels of candidate alkali stress response proteins.

Results

The response of H. tuberosus to alkali stress was detected at both physiological and molecular levels. 104 differentially expressed proteins from H. tuberosus leaves response to Na₂CO₃ treatment were successfully identified. Functional categorization of these identified proteins showed that the accumulation level of proteins involved in glycolysis, TCA cycle, PSI system, ROS scavenging and signal transduction increased under alkali stress.

Conclusions

Based on the observation of plant growth and the investigation of molecular regulation, H.tuberosus could resist certain alkali stress by modulating carbohydrate metabolism and redox homeostasis. These findings provide a new sight into the underlying molecular mechanisms of alkali resistance in plant.

     

Soil under nurse plants is always better than outside: a survey on soil amelioration by a complete guild of nurse plants across a long environmental gradient

Aims

Soil under nurse plants is more fertile than in the harsh surroundings. This is a primary mechanism involved in plant to plant facilitation and it is critical in structuring plant communities under stressful conditions. However we do not know how this soil enrichment process varies along complex environmental gradients and among coexisting nurse plants.

Methods

Soil properties related to structure, resource stocks and microbial activity, were compared among up to ten nurse plant species and adjacent barren soil areas, along a 1600 m elevation gradient above the treeline in central Chilean Andes. Shifts in Relative Interaction Index (RII) sensu Armas (Ecology 85: 2682–2686, 2004) and in coefficient of variation on soil properties were also modelled.

Results

Soil under nurse plants was always richer than on barren areas irrespective of altitude, except in the case of texture with more small particles in the intermediate altitude. β-glucosidase activity was higher under cushion plants than under nurse plants with other growth habit. Besides β-glucosidase and phosphatase activities were more variable at higher altitudes. Nitrogen was more variable under nurse plants than in barren areas and its RII values were lower at intermediate altitudes.

Conclusions

Soil amelioration by nurse plants occurred all along the studied environmental gradient promoting islands of fertility and a general increase on soil niches heterogeneity.

     

Siberian plants: untapped repertoire of bioactive endosymbionts

Background

Endosymbionts are microorganisms present in all plant species, and constitute the subject of interest among the scientific community. These symbionts have gained considerable attention in recent years, owing to their emerging biological roles. Global challenges, such as antimicrobial resistance, treatment of infectious diseases such as HIV and tuberculosis, cancer, and many genetic disorders, exist. Endosymbionts can help address these challenges by secreting valueadded bioactive compounds with various activities.

Objective

Herein, we describe the importance of plants inhabiting Siberian niches. These plants are considered to be among the least studied organisms in the plant kingdom worldwide. Barcoding these plants can be of interest for exploring bioactive endosymbionts possessing myriad biological properties.

Methods

A systematic survey of relevant scientific reports was conducted using the PubMed search engine. The reports were analyzed, and compiled to draft this review.

Results

The literature survey on Siberian plants regarding endosymbionts included a few reports, since extremely few exploratory studies have been conducted on the plants in these regions. Studies on the endosymbionts of these plants are highly valuable, as they report potent endosymbionts possessing numerous biological properties. Based on these considerations, this review aims to create awareness among the global scientific community working on related areas.

Conclusion

This review could provide the basis for barcoding novel endosymbionts of Siberian plants and their ecological importance, which can be exploited in various sectors. The main purpose of this review is to create awareness of Siberian plants, which are among the least studied organisms in the plant kingdom, with respect to endosymbionts, among the scientific community.

     

NMR-based metabolomics of transgenic and non-transgenic sweet orange reveals different responses in primary metabolism during citrus canker development

Introduction

Citrus canker, a disease caused by Xanthomonas axonopodis pv. citri (Xac) bacteria, has been responsible for extensive economic losses in citriculture. In this work, we report the metabolic responses of citrus plants during disease development. This information can be useful for understanding the natural mechanism of plant defense beyond helping design new varieties and/or genetically modified genotypes for tolerance/resistance against citrus canker.

Objectives

To understand how primary metabolism is affected in two sweet orange genotypes during citrus canker development.

Methods

¹H NMR spectroscopy together with chemometrics was used to evaluate the metabolic changes caused by Xac infection at various time points (days 4, 12 and 20) in Citrus sinensis L. Osbeck leaves from non-transgenic and transgenic plants expressing the antibacterial peptide sarcotoxin.

Results

The results revealed a high level of metabolic similarity between the studied genotypes without Xac infection. However, after Xac infection, the plants responded differently to disease development. The non-transgenic genotype showed altered early precursors of some secondary metabolites (tryptophan, tyrosine and putrescine) in addition to signaling metabolites of biotic stress (putrescine and dimethylamine), and the drastic reduction of gluconeogenesis was the overall metabolic cost for defense. The transgenic genotype suffered late metabolic changes due to the protective stoichiometric role of sarcotoxin. In addition, the oxidative stress response was more balanced in transgenic than in non-transgenic plants.

Conclusion

An NMR-based metabolomic approach was useful for understanding plant–pathogen interactions in citrus canker. Our findings provide valuable preliminary insights into different stages of citrus canker development.

     

Metabolic fingerprinting analysis of oil palm reveals a set of differentially expressed metabolites in fatal yellowing symptomatic and non-symptomatic plants

Introduction

Oil palm (E. guineensis), the most consumed vegetable oil in the world, is affected by fatal yellowing (FY), a condition that can lead to the plant’s death. Although studies have been performed since the 1980s, including investigations of biotic and abiotic factors, FY’s cause remains unknown and efforts in researches are still necessary.

Objectives

This work aims to investigate the metabolic expression in plants affected by FY using an untargeted metabolomics approach.

Method

Metabolic fingerprinting analysis of oil palm leaves was performed using ultra high liquid chromatography–electrospray ionization–mass spectrometry (UHPLC–ESI–MS). Chemometric analysis, using principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA), was applied to data analysis. Metabolites identification was performed by high resolution mass spectrometry (HRMS), MS/MS experiments and comparison with databases and literature.

Results

Metabolomics analysis based on MS detected more than 50 metabolites in oil palm leaf samples. PCA and PLS-DS analysis provided group segregation and classification of symptomatic and non-symptomatic FY samples, with a great external validation of the results. Nine differentially expressed metabolites were identified as glycerophosphorylcholine, arginine, asparagine, apigenin 6,8-di-C-hexose, tyramine, chlorophyllide, 1,2-dihexanoyl-sn-glycero-3-phosphoethanolamine, proline and malvidin 3-glucoside-5-(6″-malonylglucoside). Metabolic pathways and biological importance of those metabolites were assigned.

Conclusion

Nine metabolites were detected in a higher concentration in non-symptomatic FY plants. Seven are related to stress factors i.e. plant defense and nutrient absorption, which can be affected by the metabolic depression of these compounds. Two of those metabolites (glycerophosphorylcholine and 1,2-dihexanoyl-sn-glycero-3-phosphoethanolamine) are presented as potential biomarkers, since they have no known direct relation to plant stress.

     

Responses of rice to chronic and acute iron toxicity: genotypic differences and biofortification aspects

Background and aims

Iron (Fe) toxicity is a wide-spread stress in lowland rice production. The aim of this study was to differentiate between responses to acute Fe stress during the vegetative stage and chronic Fe stress throughout the growing period.

Methods

Six rice genotypes were tested in a semi-artificial greenhouse setup, in which acute (almost 1500 mg L^?1 Fe in soil solution during the vegetative stage) and chronic (200 to 300 mg L^?1 Fe throughout the season) Fe toxicity were simulated.

Results

Acute Fe stress induced early development of heavy leaf bronzing, whereas moderate symptoms occurred in the chronic treatment throughout the season. Grain yields were only reduced in the chronic stress treatment (?23 %) due to reductions in spikelet fertility, grain number and grain weight. Symptom formation during the early growth stages did not reflect yield responses in all genotypes. Only one genotype showed increases in grain Fe concentrations (24 % in the acute stress and 44 % in the chronic stress) compared to the control.

Conclusions

Contrasting genotypes responded differently to acute and chronic Fe toxicity, and one genotype showed consistent tolerance and the ability to translocate excess Fe into grains. These traits can be useful in the adaptive breeding of rice for Fe toxic environments.

     

Ethnobotany in a coastal environmental protected area: shifts in plant use in two communities in southern Brazil

Background

We investigated local knowledge of plants in terms of plant use shifts and losses, in two coastal communities within a protected area in southern Brazil. Our hypothesis is that people’s livelihoods are associated with different ethnobotanical knowledge, and changes in these activities can reflect shifts in ethnobotanical knowledge such as stopping using some plants.

Methods

We interviewed 125 inhabitants after prior informed consent, asking her/him about their socioeconomic profile and to free list the plants they know. The free lists were analyzed by frequency of cited plants. To compare averages of cited plants and age in both communities, we used the Wilcoxon test with a significance of 5%. Spearman correlation was tested with number of plants cited in the past and the interviewees’ age. Permanence and change in economic activities in each community were represented using a graph and compared through a chi-squared test with a significance of 5%. Qualitative analyses of the interviews and a field diary were used to analyze driving forces for the abandonment of used plants.

Results

We identified 231 plant species that were currently used mainly for food and medicine. Despite being in a protected area, most of the cited plants were exotic and cultivated in home gardens. We do not confirm the hypothesis that changes in livelihoods are reflected in the plants used; however, qualitative analyses showed potential drivers for shifts and losses of plant use. “Environmental law” and “protected area” were the drivers most related to the abandonment of plant use.

Conclusions

While recognizing the importance of the protected area to maintain local people and their traditions, we documented a shift in plant use that is mainly correlated to construction activities that disappeared from daily practices.