Effects of short-term arsenic exposure in Arabidopsis thaliana : tolerance versus toxicity responses

The metalloid arsenic (As) is highly phytotoxic, in part due to the similarity of the arsenates to phosphates, but also due to its ability to induce reactive oxygen species (ROS) formation, and in the form of arsenite directly interact with certain enzymes. Here we aimed to determine the effects of a short period of As exposure on Arabidopsis thaliana. Particular focus was given to shoot responses, which have received less attention in previous studies. A. thaliana (ecotype Col-0) plants (28-d-old) were cultivated hydroponically in the presence of 0, 27, 108, and 216 M arsenic in the form of sodium arsenate for five days. Translocation of As from root to shoot increased with increasing As concentration in the medium and caused a reduction in growth. Photosynthesis was severely affected due to stomatal closure, increased ROS accumulation, and alterations in expression of genes involved in oxidative stress responses and As detoxification. Primary metabolism was also perturbed, suggesting both the direct inhibition of certain enzymes as well as active defensive responses. Overall the effects of As toxicity depended greatly on the degree of translocation from root to shoot and involved both direct effects on biological processes and secondary effects caused by the accumulation of ROS

Transcriptional plasticity bufers genetic variation in zinc homeostasis

In roots of Arabidopsis thaliana, Zn can be either loaded into the xylem for translocation to the shoot or stored in vacuoles. Vacuolar storage is achieved through the action of the Zn/Cd transporter HMA3 (Heavy Metal Atpase 3). The Col-0 accession has an HMA3 loss-of-function allele resulting in high shoot Cd, when compared to accession CSHL-5 which has a functional allele and low shoot Cd. Interestingly, both Col-0 and CSHL-5 have similar shoot Zn concentrations. We hypothesize that plants sense changes in cytosolic Zn that are due to variation in HMA3 function, and respond by altering expression of genes related to Zn uptake, transport and compartmentalisation, in order to maintain Zn homeostasis. The expression level of genes known to be involved in Zn homeostasis were quantified in both wildtype Col-0 and Col-0::HMA3CSHL-5 plants transformed with the functional CSHL-5 allele of HMA3. We observed significant positive correlations between expression of HMA3 and of genes known to be involved in Zn homeostasis, including ZIP3, ZIP4, MTP1, and bZIP19. The results support our hypothesis that alteration in the level of function of HMA3 is counterbalanced by the fine regulation of the Zn homeostasis gene network in roots of A. thaliana

Transcriptional plasticity buffers genetic variation in zinc homeostasis

In roots of Arabidopsis thaliana, Zn can be either loaded into the xylem for translocation to the shoot or stored in vacuoles. Vacuolar storage is achieved through the action of the Zn/Cd transporter HMA3 (Heavy Metal Atpase 3). The Col-0 accession has an HMA3 loss-of-function allele resulting in high shoot Cd, when compared to accession CSHL-5 which has a functional allele and low shoot Cd. Interestingly, both Col-0 and CSHL-5 have similar shoot Zn concentrations. We hypothesize that plants sense changes in cytosolic Zn that are due to variation in HMA3 function, and respond by altering expression of genes related to Zn uptake, transport and compartmentalisation, in order to maintain Zn homeostasis. The expression level of genes known to be involved in Zn homeostasis were quantified in both wild-type Col-0 and Col-0::HMA3CSHL-5 plants transformed with the functional CSHL-5 allele of HMA3. We observed significant positive correlations between expression of HMA3 and of genes known to be involved in Zn homeostasis, including ZIP3, ZIP4, MTP1, and bZIP19. The results support our hypothesis that alteration in the level of function of HMA3 is counterbalanced by the fine regulation of the Zn homeostasis gene network in roots of A. thaliana

Arsenic s effects in seedlings of Cajanus cajan (L.) DC (Fabaceae) roots

A contaminação ambiental por arsênio (As) constitui um problema sério em várias regiões do mundo, visto que este elemento apresenta elevada toxidade para os seres vivos. Metodologias físico-químicas para detecção deste poluente no ambiente são bastante laboriosas, sendo o uso de espécies vegetais sensíveis uma boa alternativa para processos de bioindicação. Avaliações dos efeitos tóxicos do As em raízes de plântulas de Cajanus cajan (Fabaceae) foram realizadas após exposição ao poluente. Para isso, procedeu-se a análise do crescimento das raízes laterais e principal; caracterização anatômica, incluindo análises micromorfométricas e histoquímica; e avaliação da genotoxidade, por meio da determinação do índice mitótico. Os experimentos foram conduzidos em casa de vegetação, na Unidade de Crescimento de Plantas da Universidade Federal de Viçosa. No primeiro experimento, plântulas de C. cajan foram expostas, em solução nutritiva, às concentrações de 0,0 e 1,5 mg L-1 de As, na forma de arsenato de sódio, durante dez dias consecutivos. No experimento posterior foram utilizadas as concentrações de 0,0; 0,5; 1,0 e 2,0 mg L-1 de As e a exposição teve duração de três dias. A sensibilidade de C. cajan foi confirmada. Verificou-se que o As promoveu redução no crescimento da raiz principal e das laterais, estas últimas não visualizadas no tratamento com 2,0 mg L-1 de As. Contudo, microscopicamente, foi possível notar que os primórdios foram formados, mas permaneceram retidos no córtex. Notou-se que as raízes adquiriram aspecto gelatinoso e coloração escurecida com o passar do tempo de exposição. Também foram detectados problemas na formação da coifa e encurvamento do ápice radicular. A anatomia mostrou ser uma ferramenta eficiente na detecção da sensibilidade de C. cajan. Alterações anatômicas mais severas, como desintegração tecidual, nas regiões adjacentes às raízes laterais, na zona de ramificação, sugerem que esta possa ser uma importante via de entrada do poluente. Nessa mesma região células do felogênio e do câmbio apresentaram formato e planos de divisão incomuns, o que acarretou a formação de um xilema secundário assimétrico. Na zona de alongamento foram observadas células com formato alterado, indicando perda de turgidez celular. O As promoveu aumento na proporção ocupada pelo cilindro vascular, redução na proporção de espaços intercelulares no córtex, em função do maior adensamento celular nessa região, e também redução na área, em secção transversal, dos elementos de vaso. O teste histoquímico revelou acúmulo de compostos fenólicos na região do cilindro vascular e acúmulo de pectinas ao redor da raiz, possivelmente em função da ocorrência de alterações na composição química e/ou da estrutura da parede celular. A determinação do índice mitótico nos ápices radiculares evidenciou que o As apresenta elevado grau de genotoxidade, uma vez que houve um decréscimo no número de células em divisão mitótica com o incremento de As na solução nutritiva. Esse fator, aliado à redução nas taxas de alongamento celular, observada nas células corticais, são fatores que explicam a redução nas taxas de crescimento radicular.Environmental contamination by arsenic (As) is a serious problem in several regions of the world due to the high toxicity of this element. Physical-chemical methods for detection of this pollutant in the environment are quite laborious, and the use of susceptible plant species as bioindicators should be a good alternative. Assessments to the toxic effects of As in roots of seedlings of Cajanus cajan (Fabaceae) were performed after exposure of this plant to the pollutant. Growth analysis were taken for lateral and main roots, as well as anatomical characterization, including micromorphometrical analysis, histochemistry, and assessment of genotoxicity via mitotic index determination. The experiments were conducted under greenhouse condition, at the Plant Growth Unit of the Universidade Federal de Viçosa. In the first experiment, seedlings of C. cajan were grown for ten consecutive days in nutrient solutions containing 0.0 and 1.5 mg L-1 of As, in the form of sodium arsenate. In the second experiment, seedlings were grown for three days, in nutrient solutions containing 0.0, 0.5, 1.0 and 2.0 mg L-1 of As. The sensitivity of C. cajan was confirmed. It promoted the reduction in growth of main and lateral roots. Lateral roots were not even seen in the treatment containing 2.0 mg L-1 of As. However, it was possible to observe microscopically roots buts kept retained in the cortex. Moreover, roots showed a gelatinous and dark appearance, which increased with time exposure. The cap and bending of the root apex also showed developmental alterations. The anatomy technique has proved to be an effective tool in detecting the sensitivity of C. cajan to As. Severe anatomical changes, such as disintegration tissue, in particularly in the areas adjacent to the lateral roots in the zone of branching, suggested that this pathway may be an important route of entrance of the pollutant. In this same region, cells from the felogen and the cambium showed uncommon division plans, which led to an asymmetric secondary xylem. In the elongation cell zone it was observed cells of different shapes, indicating loss of cell turgidez. It was observed an increase in the proportion occupied by the vascular cylinder and a reduction in the proportion of intercellular spaces in the cortex due to a higher cells density in this region. It was also detected a reduction in area of vessels elements, in cross section. The hystochemical test revealed accumulation of phenolic compounds in the vascular cylinder and accumulation of pectins around the root, possibly due to occurrence of changes in chemical composition and/or due to structure of the cell wall. The determination of mitotic index in root apices showed that As presents high degree of genotoxicity, since there was a decrease in the number of cells in mitotic division with the increase of As in nutrient solution. This factor, combined to the reduction in the rate of cell elongation observed in cortical cells, are factors that explain the reduction in rates of root growth

Physiological changes caused by arsenic, genotoxicity and importance of mismatch repair mechanism in DNA repair in Arabidopsis thaliana

O arsênio (As) é um elemento não só tóxico, mas também altamente genotóxico aos seres vivos. Muitas lacunas precisam ser preenchidas com relação aos processos causadores de toxidade do As em plantas, bem como os mecanismos de tolerância e sensibilidade a este metalóide. Para isso, plantas de Arabidopsis thaliana (WT, mutantes msh2 e transgênicas repórteres em mutações) e Allium cepa foram expostas a 0, 2, 8 e 16 mg As L -1, durante cinco dias, em sistema hidropônico ou em meio de cultura. As plantas acumularam grandes teores de As nas raízes e apresentaram elevado fator de translocação para a parte aérea, e também alterações no acúmulo de nutrientes. Os sintomas visuais se intensificaram com o aumento da concentração de As na solução nutritiva. As raízes adquiriram coloração escura e aspecto gelatinoso, danificado e aumento no comprimento e densidade dos pêlos; a parte aérea apresentou aumento dos teores de antocianinas e sinais de senescência precoce, bem como alterações na espessura de tecidos. O estresse oxidativo e a redução dos teores de fósforo foram apontados como os principais efeitos do As capazes de causar toxidez, evidenciando os danos indiretos deste elemento no organismo. Foram verificadas importantes alterações fotossintéticas, bem como indícios de danos ao processo de respiração celular devido o aumento da expressão de genes codificantes de oxidases alternativas. Também foram observadas alterações nos teores de açúcares em folhas jovens, maduras e raízes. O As promoveu fragmentação do DNA nos ápices radiculares de A. cepa e aumento das taxas de mutação pontual e de recombinação-não homóloga em A. thaliana. O significativo aumento da expressão dos genes msh2 e msh7, codificadores de enzimas-chave do processo mismatch repair, que realiza o reparo de bases danificadas ou erroneamente inseridas no DNA, sugeriu a importância deste mecanismo no combate à genotoxidade do As em A. thaliana. Isso foi confirmado pela maior sensibilidade observada nas plantas mutantes msh2 ao As, detectada visualmente via aumento da peroxidação de lipídios. Observou-se inibição da atividade da protease caspase-3, associada ao processo de morte celular programada, reforçando a capacidade de inibição da atividade enzimática pelo As.Arsenic (As) is not only a toxic element, but also highly genotoxic to living organisms. Several gaps in our understanding of As toxicity in plants need to be filled, including the mechanisms that result in tolerance and sensitivity to this metalloid. For this reason Arabidopsis thaliana plants (WT, msh2 mutants and transgenic reporters in mutation process) and Allium cepa were exposed to 0, 2, 8 e 16 mg As L -1, for five days, in a hydroponic system or in culture medium. The plants accumulated large amounts of As in roots and presented a high translocation factor to the shoot, and also showed changes in nutrient accumulation. The visual symptoms have intensified with the increasing of As concentration in the nutritive solution. Roots showed dark coloration and a damaged and gelatinous aspect, with increased roots hair length and density. The shoots showed accumulation of anthocyanins and signs of early senescence, as well as changes in tissue thickness. Oxidative stress and reduction of phosphorus concentration in tissues have been implicated as the main cause of toxicity, evidencing the indirect damage from this element in the organism. Important changes in photosynthesis were observed, as signs of damage to respiration, due to increased expression of alternative oxidase genes. Thus, changes in the levels of synthesis and utilization of sugars by plants were observed. As promoted DNA fragmentation in A. cepa and increased rates of point mutation and nonhomologous recombination. The significant increase in the expression pattern of the msh2 and msh7 genes, which encode key enzymes in DNA repair process, suggests the importance of this mechanism in defense against As genotoxicity in A. thaliana. This was confirmed by the greater sensitivity observed in msh2 mutants to As as indicated by visual symptoms and by an increase in lipid peroxidation. Inhibition of the activity of the caspase-3 protease was also observed, evidencing the As capacity of enzyme activity inhibition.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

One “OMICS” to integrate them all: ionomics as a result of plant genetics, physiology and evolution

© 2019, Brazilian Society of Plant Physiology. The ionome concept, which stands as the inorganic composition of an organism, was introduced 15 years ago. Since then, the ionomics approaches have identified several genes involved in key processes for regulating plants ionome, using different methods and experimental designs. Mutant collections and natural variation in the model plant species Arabidopsis thaliana have been central to the recent discoveries, which are now being the basis to move at a fast pace onto other models such as rice and non-model species, aided by easier, lower-cost of genomics. Ionomics and the study of the ionome also needs integrations of different fields in plant sciences such as plant physiology, genetics, nutrition and evolution, especially plant local adaptation, while relying on methods derived from chemistry to physics, and thus requiring interdisciplinary, versatile teams. Here we review the conceptualization of the ionome as an integrated way of viewing elemental accumulation, and provide examples that highlight the potential of these approaches to shed light onto how plants regulate the ionome. We also review the main methods used in multi-element quantification and visualization in plants. Finally, we indicate what are the likely next steps to move the ionomics field forward

Phytotoxic effects of plastic pollution in crops : what is the size of the problem?

Plastic pollution is one of the most impactful human interferences in our planet. Fragmentation of plastic leads to nano- and microplastics (NP/MP) formation, which accumulate in agricultural lands, representing an increasing risk for crop production and food safety. It has been shown that MP promote damage in plant tissues by several direct and indirect ways, and that NP can enter the tissues/cells and accumulate in edible organs. Investigation of the phytotoxic effects of NP/MP in plants started only in 2016, with most of the studies performed with crops. Since contradictory results are often observed, it is important to review the literature in order to identify robust effects and their possible mechanisms. In this review, we discuss the potential of NP/MP in damaging crop species, with focus on the physiological changes described in the literature. We also performed scientometrics analyses on research papers in this field during 2016–2021, to reveal the research situation of phytotoxic effects of plastic pollution in crops. Our review is as a starting point to help identify gaps and future directions in this important, emerging field