Singlet oxygen initiates a plastid signal controlling photosynthetic gene expression.

Retrograde signals from the plastid regulate photosynthesis-associated nuclear genes and are essential to successful chloroplast biogenesis. One model is that a positive haem-related signal promotes photosynthetic gene expression in a pathway that is abolished by the herbicide norflurazon. Far-red light (FR) pretreatment and transfer to white light also results in plastid damage and loss of photosynthetic gene expression. Here, we investigated whether norflurazon and FR pretreatment affect the same retrograde signal. We used transcriptome analysis and real-time reverse transcription-polymerase chain reaction (RT-PCR) to analyse the effects of these treatments on nuclear gene expression in various Arabidopsis (Arabidopsis thaliana) retrograde signalling mutants. Results showed that the two treatments inhibited largely different nuclear gene sets, suggesting that they affected different retrograde signals. Moreover, FR pretreatment resulted in singlet oxygen (1 O2 ) production and a rapid inhibition of photosynthetic gene expression. This inhibition was partially blocked in the executer1executer2 mutant, which is impaired in 1 O2 signalling. Our data support a new model in which a 1 O2 retrograde signal, generated by chlorophyll precursors, inhibits expression of key photosynthetic and chlorophyll synthesis genes to prevent photo-oxidative damage during de-etiolation. Such a signal would provide a counterbalance to the positive haem-related signal to fine tune regulation of chloroplast biogenesis.This work was funded by BBSRC grants 51/P17214 and BB/ J018139/1 to M.J.T. and BB/J018694/1 to A.G.S

Rising atmospheric temperature impact on wheat and thermotolerance strategies

Temperature across the globe is increasing continuously at the rate of 0.15–0.17 °C per decade since the industrial revolution. It is influencing agricultural crop productivity. Therefore, thermotolerance strategies are needed to have sustainability in crop yield under higher temperature. However, improving thermotolerance in the crop is a challenging task for crop scientists. Therefore, this review work was conducted with the aim of providing information on the wheat response in three research areas, i.e., physiology, breeding, and advances in genetics, which could assist the researchers in improving thermotolerance. The optimum temperature for wheat growth at the heading, anthesis, and grain filling duration is 16 ± 2.3 °C, 23 ± 1.75 °C, and 26 ± 1.53 °C, respectively. The high temperature adversely influences the crop phenology, growth, and development. The pre-anthesis high temperature retards the pollen viability, seed formation, and embryo development. The post-anthesis high temperature declines the starch granules accumulation, stem reserve carbohydrates, and translocation of photosynthates into grains. A high temperature above 40 °C inhibits the photosynthesis by damaging the photosystem-II, electron transport chain, and photosystem-I. Our review work highlighted that genotypes which can maintain a higher accumulation of proline, glycine betaine, expression of heat shock proteins, stay green and antioxidant enzymes activity viz., catalase, peroxidase, super oxide dismutase, and glutathione reductase can tolerate high temperature efficiently through sustaining cellular physiology. Similarly, the pre-anthesis acclimation with heat treatment, inorganic fertilizer such as nitrogen, potassium nitrate and potassium chloride, mulches with rice husk, early sowing, presoaking of a 6.6 mM solution of thiourea, foliar application of 50 ppm dithiothreitol, 10 mg per kg of silicon at heading and zinc ameliorate the crop against the high temperature. Finally, it has been suggested that modern genomics and omics techniques should be used to develop thermotolerance in wheat.Higher Education Commission (HEC) Pakistan | Ref. 1a55b19f0b99ca1

THE ECO-PHYSIOLOGY, STRESS RESPONSE REGULATION, AND ENGINEERING OF SHEWANELLA SPECIES FOR INDUSTRIAL AND ENVIRONMENTAL APPLICATIONS

In recent decades, there has been tremendous interest in applying environmental microbiology for waste treatment, bioremediation and sustainable energy production. As one of the most important model environmental microbes, Shewanella species are renowned for their flexible growth, capability of surviving and growing in a wide gradient of various environmental conditions, and excellent respiratory versatility. There is great prospect of using this organism for production of valuable chemicals, treatment of various types of contamination, and for energy generation in Microbial Fuel Cells. However, the real-life application of Shewanella is hindered by the relatively low level of performance. Fundamental knowledge of the physiology, ecology, stress response mechanism, as well as correct engineering, are indispensable for discovering novel properties and to boost the performance of Shewanella-based applications. In an initial effort of understanding gene functions and regulations, a particularly interesting mutant of Shewanella loihica PV-4 that could accumulate significant amount of red pigmentation was identified via transposon mutant library screening. The mutation was then found to be on gene Shew_2229 which encodes ferrochelatase. Using analytical methods, the red pigment was verified as protoporphyrin IX (PPIX), an important chemical involved in the synthesis of hemoglobin. Quantification of the yield of PPIX in this mutant was estimated to be 11.2mg/g cell dry weight, which was at least hundreds of times higher compared to other reported bacterial strains and similar to the level of a fully engineered strain that require multiple types of antibiotics to be supplied for its fermentation. A patent for using this PV-4 mutant strain for industrial production of PPIX was issued (US patent No. 9273334B2). Of great interest was that, the genome of PV-4 contains two paralogues of the hemH gene, designated as hemH1 (Shew_2229) and hemH2 (Shew_1140). It was discovered that single disruption of hemH1 resulted in PPIX accumulation, while single disruption of hemH2 had no apparent phenotype. Therefore, it is hypothesized that there is functional redundancy among the two paralogues with hemH1 as the dominant gene and hemH2 playing a supplementary role. To test this hypothesis, the regulation mechanisms of hemH1 and hemH2 were analyzed via comparative genomics. Sequence analysis of the promoter region of the two paralogues indicated that the two genes were regulated differently. The promoter sequence of hemH1 contains the binding box of the constitutively expressed sigma factor RpoD, while the promoter sequence of hemH2 harbors the binding sequence of the extracellular family sigma factor RpoE2, which suggested that the expression of the two paralogues might be different. Consistently, hemH1 was found constitutively expressed while expression of hemH2 was minimal in presence of a non-disrupted hemH1 but increased significantly when hemH1 was disrupted, supporting the supplementary role of hemH2 in PV-4. Besides, the up-regulation of hemH2 was also observed when PV-4 was exposed to the oxidative stress, either by introduction of hydrogen peroxide or due to accumulation of the photosensitive PPIX. We found that expression of hemH2 was significantly higher when the hemH1 mutant was exposed to light, and accumulation of PPIX was no longer observed under such condition. All these findings suggest that hemH2 plays a more important role under oxidative stressed conditions although its expression is minimal under normal conditions. The apparent redundancy of the hemH paralogues may contribute to the survival of this strain under stress conditions. Salt stress is one of the most commonly observed stresses for microbes in the natural environment. It is often associated with environmental pollution and can be introduced during bioremediation processes, such as neutralizing pH for sites with high acidity or alkalinity. Understanding the mechanism for salt stress response of microbes is a fundamental step toward boosting the performance of environmental microbiology applications. Although there has been ample documentation regarding the salt stress response in various microbes, knowledge about the microbial response to long term salt stress is lacking. The Shewanella putrefaciens CN-32 strain is an excellent candidate for bioremediation or MFCs. Using the strategy of experimental evolution, the response to salt (NaCl) stress over long term lab incubation was investigated. The changes of growth phenotype, metabolite profile, and transcriptome in evolved populations were analyzed. The mutations occurred in evolved populations were captured by sequencing population DNAs to help interpret fitness changes. Profound differences in phenotypes were observed among the evolved populations. Populations evolved under salt stress (ES) exhibited significant advantage in growth rate and peak biomass compared with populations evolved under control conditions (EC) or ancestor (AN), indicating gain of fitness. However, the evolved populations were inferior in terms of motility compared to the ancestor, likely one of the tradeoffs during the evolutionary course. Analysis of metabolite profile via Detrended Correspondence Analysis showed that culture condition (salt stress vs. control) and the condition of evolution are the key factors shaping the metabolite composition. Interesting patterns of metabolites were identified, such as the significant higher amount of two compatible solutes, proline and ectoine, in the ES populations, indicating that these two metabolites may play critical role for salt tolerance in this organism. Transcriptome analysis of select populations revealed that significant up-regulation of genes involved in proline uptake and synthesis was shared across the populations, again reflected the importance of proline accumulation for salt stress protection. Whole-genome-resequencing revealed interesting mutations that may contribute to the improved salt tolerance in ES populations. The potential application of Shewanella species as bioanode for electricity generation in MFCs was investigated. Redox polymer was introduced with the aim of boosting current generation. The effect of various factors was investigated, such as different Shewanella strains, loading of the redox polymer, and methods of bacteria incorporation. The results showed that electrode surface modification by coating of PVP-Os redox polymer led to several folds of increase in current density. Among the four strains studied, namely Shewanella oneidensis MR-1, Shewanella putrefaciens W3-18-1, Shewanella loihica PV-4, and Shewanella putrefaciens CN-32, strain W3-18-1 showed the best current density with or without redox polymer. Using W3-18-1 as the target organism, the effect of polymer loading, and methods of incorporation were further investigated. Increased amount of PVP-OS loading alone did not lead to an increase of current density, as the increased thickness might perturb efficient electron communication between the redox centers. Four different methods of bacteria incorporation with PVP-OS were compared, the suspension method, lay-over method, mix and cast method, and layer-by-layer method using a gold electrode. The layer-by-layer method produced significantly higher current density compared with other methods, but take longer time to reach peak current density. The suspension method showed second highest current density and quickest response, while the LO and MAC methods showed significantly lower current density. In summary, the mechanisms of PPIX accumulation and oxidative stress response in Shewanella loihica PV-4, the long term salt adaptation in Shewanella putrefaciens CN-32, and current generation in several Shewanella strains, were investigated via systematic analysis of mutagenesis, functional genomics, comparative genomics, and electrochemistry. Results of this study expands our current knowledge of the physiology, genetics, stress response, and evolution of the Shewanella genus, providing important clues for environmental applications such as bioremediation and MFC, as well as using this type of organism for industrial production of valuable chemicals such as PPIX

Dynamics of Microbial Communities in Nitrite-Free and Nutritionally Improved Dry Fermented Sausages

Dry fermented sausage innovation trends are linked to consumer preferences for clean label and sodium-reduced foods. This study aims to evaluate the effect of the formulation and production process temperature on the dynamics of bacterial communities in fuet-type dry fermented sausages using metataxonomics. Six fuet batches were manufactured, including formulations without and with the addition of nitrifying salts (replaced or not by pork liver auto-hydrolysate as a colouring agent), processed at 3 to 12 °C, and a partial replacement of NaCl by KCl, processed at 12 °C. Fermentation was performed spontaneously or by a starter culture. Physicochemical characterisation and culture-dependent and independent bacterial analyses were performed at day 0, 4 and 12, at the end of ripening (aw < 0.90) and after storage. Temperature was the most important factor determining the change in pH, aw and lactic acid bacteria levels while the presence of a starter culture promoted a pH decrease. Metataxonomic analysis showed that low temperature processes and the absence of nitrifying salts allowed the growth of spoilage-related species, while sausages submitted to a mild temperature containing a starter culture and nitrifying salts showed less bacterial diversity. Liver auto-hydrolysate added putative probiotic species to the product. This study provides valuable information to manufacturers who want to innovate safely.info:eu-repo/semantics/publishedVersio

A genomic analysis using RNA-Seq to investigate the adaptation of the psychrophilic diatom Fragilariopsis cylindrus to the polar environment

Diatoms are unicellular photosynthetic eukaryotes with a silicate cell wall. They often dominate polar marine ecosystems, driving the major biogeochemical cycles in these areas. The obligate psychrophilic diatom Fragilariopsis cylindrus is a keystone species in the Southern Ocean. It thrives both in open waters and sea ice and has become a model for studying eukaryotic microalgal adaptations to polar marine conditions. The aim of this thesis was to identify how the genome of F. cylindrus has evolved to cope with marine environmental conditions of the Southern Ocean. To identify key genes, comparative genomics, high-throughput transcriptome sequencing and reverse genetics were applied. Comparative genomics with the sequenced mesophilic diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana was combined with genome-wide RNA-Seq transcriptome analysis, leading to the discovery a new bacteria-like rhodopsin not present in other sequenced diatoms. The characterisation of a bacteria-like rhodopsin in F. cylindrus was conducted by applying reverse genetics tools. The genome was characterised by a low G+C content, which affected codon usage. High sequence polymorphism resulted in pronounced unequal expression of putative heterozygous allelic gene copies in response to six different conditions. RNA-Seq detected transcriptional activity for 95% of the 27,137 predicted genes and > 4 fold expression changes between 55% of putative alleles. The most significant transcriptional changes were detected during prolonged darkness affecting 70% of genes and 30% of RNA-Seq reads mapped to unannotated regions of the genome. Two rhodopsin alleles showed unequal bi-allelic expression in response to iron starvation and heterologous expression in Xenopus laevis oocytes experimentally confirmed light-driven proton pumping for the iron-induced rhodopsin allele, suggesting significance for the adaptation of F. cylindrus to environmental conditions of the Southern Ocean. These data show how the polar environment can shape the genome of a eukaryotic phytoplankton in unprecedented detail. High numbers of species-specific genes resulting in expansion of gene and protein families, low G+C likely enabling efficient translation at low temperatures and a high degree of heterozygosity combined with unequal bi-allelic expression, may provide an adaptive strategy to polar conditions by conferring metabolic flexibility and capacity to adapt to a rapidly changing environment

Iron metabolism at the interface between host and pathogen: From nutritional immunity to antibacterial development

Nutritional immunity is a form of innate immunity widespread in both vertebrates and invertebrates. The term refers to a rich repertoire of mechanisms set up by the host to inhibit bacterial proliferation by sequestering trace minerals (mainly iron, but also zinc and manganese). This strategy, selected by evolution, represents an effective front-line defense against pathogens and has thus inspired the exploitation of iron restriction in the development of innovative antimicrobials or enhancers of antimicrobial therapy. This review focuses on the mechanisms of nutritional immunity, the strategies adopted by opportunistic human pathogen Staphylococcus aureus to circumvent it, and the impact of deletion mutants on the fitness, infectivity, and persistence inside the host. This information finally converges in an overview of the current development of inhibitors targeting the different stages of iron uptake, an as-yet unexploited target in the field of antistaphylococcal drug discovery

Unravelling the molecular and physiological components that contribute to iron deficiency chlorosis

Iron (Fe) deficiency chlorosis (IDC) is a serious condition affecting plants which are grown under calcareous or water logged soils. Under such conditions,Fe forms insoluble oxides and becomes unavailable for plant uptake, leading to stunted growth and severe yield reduction, causing aggravated agricultural losses. In the past years,efforts have been made to increase plant Fe content(so-called plant biofortification), in order to reduce the incidence of iron deficiency anaemia (IDA) prevalent around the world. To this end, legume grains and cereals, due to their rich nutritional profile and high worldwide intake by the population,have gained an important role in biofortification studies, which depend on the available molecular and physiological data for their successful implementation. The aim of this thes is was to contribute to the understanding of the molecular, physiological and biochemical mechanisms associated to Fe uptake and transport in Fe-stressed plants and to test a new class of Fe chelates as an efficient tool to prevent IDC. With the purpose of understanding the transcriptomic response to Fe deficiency in a set of different legume species, a non-targeted analysis was performed using Illumina technology. Transcriptome analysis was performed in the roots of soybean (Glycine max), common bean (Phaseolus vulgaris) and barrel medic (Medicago truncatula) grown in Fe deficiency and Fe sufficiency, and 114,723 annotated genes were obtained for all samples. Four IDC-related gene families were up-regulated in common by the three species and can be considered key players involved in the IDC response, namely, metal ligands, transferases, zinc ion binding and metal ion binding genes. Also, amongst the most highly expressed genes were genes of theisoflavonoid pathway and, on the other hand, oxidoreductases were the most down-regulated genes.Still on the search for IDC molecular players, two targetedgenetic analyses were performed,one on G.maxand M. truncatula and another on rice (Oryza sativa). Both studies involved the growth of plants under Fe sufficiency and Fe deficiency in order to compare the regulation of IDC related genes. Soybean and barrel medicare strategy I-crops,which means that, before uptake, they need to reduce Fe(III) to Fe(II) via an enzyme encoded by the FRO2 gene and, afterwards, Fe(II) is transported to the roots via ametal transporter encoded by the IRT1 gene. The expression of these two genes was analysed and both behaved similarly between species, appearingto be co-regulated.Moreover, the Fe transportersYSL1 andVIT1and the main Fe storage protein-encoding gene –ferritin–were up-regulated in the presence of Fe. The NRAMP3 gene, responsible for Fe remobilization from the vacuoles, was up-regulated under Fe deficiency,as was theGCN2gene, indicating a putative role of the latterin Fe metabolism and homeostasis.The targeted study performed in rice, a strategy II cereal that releases phytosiderophores in order to chelate and absorb Fe, involved the analysis of two rice cultivars with distinct susceptibilities to IDC –cv. Nipponbare and cv. Bico Branco. This different susceptibility was confirmed by their contrasting leaf chlorosis development and tissue nutrient accumulation patterns. Thecv. Nipponbare, that showed lower IDC susceptibility, was able to induce higher levels of the key reduction enzyme activity(Fe reductase)and showed higher levels of expression of the strategy I-OsFRO2 gene in roots.In contrast, cv. Bico Branco induced more genes involved in strategy II, specially, the transcription factor OsIRO2 and the phytosiderophore precursor OsTOM1.The screening for tolerant genotypes to IDC is an important tool in plant breeding programs. The most common IDC indicator is the degree of chlorosis development, which is quantified using a numerical scale. Therefore, after gathering the molecular data, the physiological mechanisms triggered by IDC were studied. The model crop G. max was selected,as it comprises lines well characterized according to their IDC-susceptibilities. To this end, two studies were performed. In the first study we aimed at understanding if the ability to partition Fe could be related to Fe-efficiency. We concluded that IDC susceptible lines, when compared to efficient lines,have lower ability to translocate Fe to the shoots, having about two fold higher Fe content at the root level, and they have lower capacity to induce the ferric reductase enzyme, having about three fold lower enzyme activity. In the second study the regulation of the antioxidant and tetrapyrrole systems under Fe deficiency was analysedfor the first time and we inferred that higher levels of oxidative stress might induce the oxidation of the tetrapyrrole heme into hemin, which leads to the induction of the heme-containing catalase enzyme and the reduction of ferric reductase activity. Taken together, the previous results indicate that low ferric reductase activity and Fe accumulation in the root tissue could be added as new IDC-related physiological markers.The application of fertilizers and Fe chelating agentsis one of the most frequently used tools to manage IDC. However, most of them are ineffective,too expensive or recalcitrant in the environment. Hence, the search for new Fe chelates is of utmost importance. In the last step of this thesis, we investigated the potential of a tris(3-hydroxy-4-pyridinonate) Fe(III) complex(Fe(mpp)3, which has never be enutilized in agricultural context)as na Fe fertilizer. Soybean plants were grown hydroponically under Fe deficiency and with Fe(mpp)3or Fe EDDHA supplementation. Results of both physiological and molecular markers showed that the new Fe complex led to healthier plants with increased growthby 24%,42% higher SPAD units and lower Fe retention in the roots.In general, the results presented in this thesis have contributed to a better understanding of the IDC-associated mechanisms and elucidated the key factors to be considered when analysing Fe deficient plants and their defence responses.Aclorose por deficiência de ferro (Fe) é uma condição grave que afeta plantas em solos calcários ou alagados. Sob estas condições, o Fe forma óxidos insolúveis e torna-se indisponível para absorção pelas plantas, o que conduz a um crescimento diminuído e a uma redução severa na produção, resultando em perdas agronómicas agravadas. Nos últimos anos, têm sido desenvolvidos estudos no sentido de aumentar o conteúdo de Fe nos tecidos vegetais (biofortificação), de forma a reduzir a incidência da anemia por deficiência de Fe prevalente no mundo. Com este objetivo, as leguminosas e os cereais, dado o seu perfil nutricional rico e o seu alto consumo pela população mundial, têm ganho particular enfoque nos estudos de bio fortificação, cujos resultados dependem da informação molecular e fisiológica disponível. O objetivo do presente trabalho foi contribuir para a compreensão dos mecanismos moleculares, fisiológicos e bioquímicos associados à absorção e transporte de Fe, bem como o estudo do potencial de uma nova classe de quelantes de Fe como uma ferramenta eficaz na prevenção da clorose férrica.Com o objetivo de compreender a resposta transcritómica à deficiência de Fe num conjunto de diferentes espécies de leguminosas, foi realizada uma análise não-direcionada com recurso à tecnologia Illumina. A análise transcritómica foi realizada nas raízes de soja (Glycine max), feijão (Phaseolus vulgaris) e luzerna-cortada (Medicago truncatula), crescidas em deficiência ou suficiência de Fe. Deste estudo, identificaram-se114.723 genes para todas as amostras. Quatro famílias de genes, nomeadamente ligandos de metais, transferases, proteína quinase e genes de ligação a metais e iões de zinco, foram sobre-expressas pelas três espécies e podem ter um papel relevante na resposta à clorose férrica. Entre os genes específicos mais expressos em deficiência de Fe, identificaram-se também genes da via dos isoflavonóides. Por outro lado, entre os genes cuja expressão foi diminuída sob deficiência de Fe, identificaram-se genes codificantes de oxidoreductases. Realizaram-se também dois estudos direcionados, um em G. maxe M. truncatulae outro em arroz (Oryza sativa). Ambos os estudos implicaram o crescimento de plantas com e sem suplementação de Fe, por forma a comparar a regulação de genes relacionados com a clorose férrica. A soja e a luzerna-cortada são leguminosas que utilizam a estratégia I, o que significa que, antes da absorção pelas raízes, elas necessitam de reduzir o Fe (III) a Fe(II) utilizando uma enzima codificada pelo gene FRO2 e, depois deste passo, o Fe (II) é transportado por um transportador de metais codificado pelo gene IRT1. A expressão destes dois genes foi estudada e verificou-se que ambos comportaram-se de forma semelhante entre espécies, sugerindo que a sua expressão é co-regulada. Estudaram-se também os transportadores de Fe YSL1 e VIT1, e o gene codificante da principal proteína de armazenamento de Fe –a ferritina–tendo sido todos sobre-expressos na presença de Fe. O gene NRAMP3, responsável pela remobilização do Fe dos vacúolos, foi sobre-expresso na deficiência de Fe, tal como o gene GCN2, o que sugeriu um possível papel deste último no metabolismo e homeostasia do Fe. No estudo realizado com o arroz, um cereal que utiliza a estratégia IIe que liberta fitosideróforos para quelatar e absorver o Fe, analisaram-se duas cultivares de arroz com suscetibilidades distintas à clorose férrica–cv. Nipponbare e cv. Bico Branco. A suscetibilidade diferencial foi confirmada pelo padrão oposto obtido nos resultados do desenvolvimento da clorose férrica e da acumulação de nutrientes nos tecidos. A cv. Nipponbare, que demonstrou menor suscetibilidade à clorose férrica, induziu níveis mais altos da enzima reductase férrica nas raízes, responsável pela redução de Fe(III), assim como do gene correspondente, OsFRO2, típico da estratégia I. Pelo contrário, a cv. Bico Branco induziu maiores níveis dos genes envolvidos na estratégia II, em particular, o fator de transcrição OsIRO3 e o precursor de fitosideróforos OsTOM1.A seleção de cultivares tolerantes à deficiência de Fe é uma ferramenta importante para programas de melhoramento de plantas. O indicador de clorose férrica mais comum é o grau de desenvolvimento de clorose, que é quantificado com uma escala numérica. Assim, após reunir os dados moleculares, estudaram-se os mecanismos fisiológicos associados à clorose férrica. A soja foi selecionada como espécie-modelo pelo facto de incluir diversas linhas amplamente caracterizadas de acordo com a sua suscetibilidade à clorose férrica. Deste modo, este estudo foi dividido em duas análises principais. Na primeira análise,o objetivo foi compreender se a capacidade de partição de Fe podia ser relacionada com a eficiência de Fe. Concluiu-se que as linhas suscetíveis, em comparação com as linhas eficientes, tiveram uma capacidade menor de translocação do Fe para a parte aérea da planta, acumulando cerca do dobro do conteúdo de Fe nas raízes e, mais ainda, estas linhas tinham também níveis três vezes mais baixos de atividade da enzima reductase. Na segunda análise estudou-se, pela primeira vez, a regulação dos sistemas antioxidante e tetrapirrólico na deficiência de Fe e observou-se que níveis superiores de stress oxidativo podem induzir a oxidação da molécula heme em hemina, que resulta na indução da enzima catalase e na redução da atividade da enzima reductase, sendo que ambas possuem o grupo heme na sua estrutura. Em suma, os resultados anteriores indicam que uma atividade baixa da enzima reductase férrica e acumulação de Fe nas raízes podem ser novos indicadores fisiológicos para a clorose férrica. A aplicação de fertilizantes e de agentes quelantes de Fe é uma das estratégias mais utilizadas para tratar a clorose férrica. Porém, muitos destes produtos são ineficazes, dispendiosos ou recalcitrantes no ambiente. Como tal, o desenvolvimento de novos quelatos de Fe é de extrema importância. Na última parte desta tese investigou-se o potencial de um complexo do grupo tris (3-hydroxy-4-pyridinonate) Fe (III) (Fe (mpp)3, nunca utilizado em contexto agronómico)como um fertilizante novo de Fe. Plantas de soja foram crescidas em hidroponia sob deficiência de Fe ou suplementadas com Fe(mpp)3ou Fe EDDHA. Quer os resultados dos marcadores fisiológicos, quer dos moleculares demonstraram que, com o novo complexo de Fe, as plantas desenvolveram-se de forma mais saudável, obtendo um crescimento superior em 24%, 42% maior acumulação de clorofilas e menor retenção de Fe nas raízes. Em geral, os resultados apresentados nesta tese contribuíram para uma melhor compreensão dos mecanismos associados à clorose férrica e esclareceram alguns dos fatores chave a considerar na análise das respostas de defesa de plantas sob stress de ferro