Antioxidant and drought-acclimation responses in UV-B-exposed transgenic Nicotiana tabacum displaying constitutive overproduction of H2O2.

Hydrogen peroxide (H2O2) is an important molecule that regulates antioxidant responses that are crucial for plant stress resistance. Exposure to low levels of ultraviolet-B radiation (UV-B, 280-315 nm) can also activate antioxidant defenses and acclimation responses. However, how H2O2 and UV-B interact to promote stress acclimation remains poorly understood. In this work, a transgenic model of Nicotiana tabacum cv Xanthi nc, with elevated Mn-superoxide dismutase (Mn-SOD) activity, was used to study the interaction between the constitutive overproduction of H2O2 and a 14-day UV-B treatment (1.75 kJ m-2 d-1 biologically effective UV-B). Subsequently, these plants were subjected to a 7-day moderate drought treatment to evaluate the impact on drought resistance of H2O2- and UV-dependent stimulation of the plants' antioxidant system. The UV-B treatment enhanced H2O2 levels and altered the antioxidant status by increasing the epidermal flavonol index, Trolox Equivalent Antioxidant Capacity, and catalase, peroxidase and phenylalanine ammonia lyase activities in the leaves. UV-B also retarded growth and suppressed acclimation responses in highly H2O2-overproducing transgenic plants. Plants not exposed to UV-B had a higher drought resistance in the form of higher relative water content of leaves. Our data associate the interaction between Mn-SOD transgene overexpression and the UV-B treatment with a stress response. Finally, we propose a hormetic biphasic drought resistance response curve as a function of leaf H2O2 content in N. tabacum cv Xanthi.

Ultraviolet-B exposure and exogenous hydrogen peroxide application lead to cross-tolerance toward drought in Nicotiana tabacum L.

Acclimation of plants to water deficit involves biochemical and physiological adjustments. Here, we studied how ultraviolet (UV)-B exposure and exogenously applied hydrogen peroxide (H2 O2 ) potentiates drought tolerance in tobacco (Nicotiana tabacum L. cv. xanthi nc). Separate and combined applications for 14 days of 1.75 kJ m-2  day-1 UV-B radiation and 0.2 mM H2 O2 were assessed. Both factors, individually and combined, resulted in inhibition of growth. Furthermore, the combined treatment led to the most compacted plants. UV-B- and UV-B + H2 O2 -treated plants increased total antioxidant capacity and foliar epidermal flavonol index. H2 O2 - and UV-B + H2 O2 -pre-treated plants showed cross-tolerance to a subsequent 7-day moderate drought treatment, which was assessed as the absence of negative impact on growth, leaf wilting, and leaf relative water content. Plant responses to the pre-treatment were notably different: (1) H2 O2 increased the activity of catalase (EC 1.11.1.6), phenylalanine ammonia lyase (EC 4.3.1.5), and peroxidase activities (EC 1.11.1.7), and (2) the combined treatment induced epidermal flavonols which were key to drought tolerance. We report synergistic effects of UV-B and H2 O2 on transcription accumulation of UV RESISTANCE LOCUS 8, NAC DOMAIN PROTEIN 13 (NAC13), and BRI1-EMS-SUPPRESSOR 1 (BES1). Our data demonstrate a pre-treatment-dependent response to drought for NAC13, BES1, and CHALCONE SYNTHASE transcript accumulation. This study highlights the potential of combining UV-B and H2 O2 to improve drought tolerance which could become a useful tool to reduce water use.

Elicitores: implicaciones bioéticas para la agricultura y la salud humana / Elicitors: bioethical implications for agriculture and human health / Elicitores: implicações bioéticas para a agricultura e a saúde humana

Resumen Los compuestos agroquímicos se han utilizado en la agricultura en las últimas décadas para evitar pérdidas por plagas, nutrir la tierra, aumentar el rendimiento y la calidad de los cultivos. Sin embargo, el uso de estas sustancias en muchas ocasiones representa una fuente de contaminación ambiental y riesgos a la salud. Por ello, han surgido nuevas alternativas en la producción alimentaria, como el uso de elicitores, para consolidar una agricultura más sostenible y sin efectos adversos a la salud del consumidor. Los elicitores pueden estimular el metabolismo propio de las plantas para producir compuestos que resultarán en rasgos agronómicos deseados, como metabolitos secundarios de uso nutracéutico. En el presente artículo se muestra la perspectiva científica y ética de proyectos de investigación en los cuales se emplean diferentes elicitores para sustituir el uso de agroquímicos.

Abstract In recent decades, agrochemicals have been used in agriculture to increase crop yields and quality and avoid losses due to pests. However, the use of these substances often imply environmental contamination and potential health risks. To move towards a more sustainable agriculture with less undesirable effects to human health, a novel line of research has recently emerged, proposing alternatives for the use of agrochemicals, such as elicitors. Elicitors, either biotic or abiotic, can stimulate plants biochemical mechanism to produce compounds that will result in desired agronomic traits, such as secondary metabolites to be used as nutraceuticals. This article shows the scientific and the ethic perspective of research projects evaluating the role of different elicitors in replacing the use of agrochemicals.

Resumo Nas últimas décadas, compostos agroquímicos têm sido utilizados na agricultura para evitar pragas, nutrir o solo e aumentar a produtividade e a qualidade das plantas. No entanto, o uso dessas substâncias muitas vezes contamina o meio ambiente e traz riscos à saúde. Por isso, novas alternativas, como os elicitores, surgiram na produção alimentar a fim de consolidar uma agricultura mais sustentável, sem efeitos adversos para a saúde do consumidor. Os elicitores podem estimular o próprio metabolismo das plantas para produzir compostos que resultarão em características agronômicas desejadas, como metabólitos secundários para uso nutracêutico. Este artigo mostra a perspectiva científica e ética de projetos de pesquisa em que diferentes elicitores substituem agroquímicos.

Response of transgenic tobacco overexpressing the CchGLP gene to cadmium and aluminium: phenotypic and microRNAs expression changes.

Transgenic tobacco (N. tabacum cv. Xanthi nc) expressing Capsicum chinense CchGLP gene that encodes an Mn-SOD, constitutively produces hydrogen peroxide that increase endogenous ROS levels. Previous studies using these plants against geminivirus infections as well as drought stress confirmed that CchGLP expression conferred resistance against biotic and abiotic stresses. Cadmium (Cd) and Aluminium (Al) contamination in soils are a major ecological concern since they are two of the most widespread toxic elements in terrestrial environments. Trying to explore additional possible tolerance to another stresses in these plants, the aim of this work was to analyse the response to cadmium and aluminium salts during germination and early stages of plantlet development and a differential transcriptome of microRNAs (miRNAs) expression in expressing CchGLP transgenic lines and an azygote non-CchGLP expressing line. Plants were grown in vitro with addition of CdCl2 and AlCl3 at three different concentrations: 100, 300 and 500 µM and 50, 150 and 300 µM, respectively. The results showed higher tolerance to Cd and Al salts evaluated in two CchGLP-expressing transgenic lines L8 and L26 in comparison with the azygous non-CchGLP expressing line L1. Interestingly, L8 under Al stress presented vigorous roots and development of radicular hairs in comparison with azygous control (L1). Differentially expressed miRNAs in the comparison between L8 and L1 were associated with up and down-regulation of target genes related with structural molecule activity and ribosome constituents, as well as down-regulation in proton-transporting V-type ATPase (Vacuolar ATPase or V-ATPase). Moreover, KEGG analysis of the target genes for the differentially expressed miRNAs, led to identification of genes related with metabolic pathways and biosynthesis of secondary metabolites. One possible explanation of the tolerance to Cd and Al displayed in the transgenic tobaccos evaluated, might involve the fact that several down-regulated miRNAs, were found associated with target genes expressing V-ATPase. Specifically, miR7904-5p was down regulated and related with the up-regulation of one V-ATPase. The expression levels of these genes was confirmed by qRT-PCR assays, thus suggesting that a cation transport activity driven by the V-ATPases-dependent proton motive force, might significantly contribute as one mechanism for Cd and Al detoxification by vacuolar compartmentation in these transgenic tobacco plants.