Respostas de enzimas antioxidantes a bioestimulantes em plantas de milho e de soja sob estresse hídrico

Water stress is one of the most important environmental factors inducing physiological changes in plants, such as decrease in the water potential of the cells, the stomatal closure; and the development of oxidative processes mediated by reactive oxygen species (ROS). Antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) are efficient scavengers of ROS. The aim of this research was to examine how the application of biostimulant based on humic substances and aminoacids may affect activity levels of SOD, CAT, and APX of maize and soybean plants under well-watered or drought stress conditions. Pots (4.5 L) were filled with a Typic Hapludult soil where the biostimulants doses were applied. It was taken leaf samples in order to analyze SOD, CAT, and APX activities in plants. SOD and APX activity levels were increased by application of biostimulant 1 in maize subjected to stress. Catalase activity was not enhanced in plants by using the biostimulants. The composition of the biostimulants was not able to enhance stress tolerance in maize and soybean plants subjected to water stress.O estresse hídrico é um dos mais importantes fatores ambientais que induz mudanças fisiológicas, como diminuição do potencial de água na célula, o fechamento dos estômatos e o desenvolvimento de processos oxidativos mediante a formação das espécies reativas de oxigênio (ROS). As enzimas antioxidantes superóxido dismutase (SOD), catalase (CAT) e ascorbato peroxidase (APX) são eficientes eliminadores das ROS. O objetivo deste estudo foi examinar como a aplicação de bioestimulantes com substâncias húmicas e aminoácidos em sua composição afeta os níveis de SOD, CAT e APX nos tecidos das folhas de plantas de milho e de soja cultivadas com ou sem estresse hídrico. Amostras de um Argissolo foram colocadas em vasos (4,5 L) onde foram adicionadas as doses dos bioestimulantes. Foram retiradas amostras de folhas para análise da atividade da SOD, CAT e APX nas plantas. A SOD e APX aumentaram nas plantas de milho com a aplicação do bioestimulante 1. A atividade da CAT não aumentou nas plantas com a aplicação dos bioestimulantes. As composições dos bioestimulantes não possibilitaram aumento na resistência ao estresse hídrico em plantas de milho e de soja submetidas ao estresse hídricoCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

SacB-SacR Gene Cassette As the Negative Selection Marker to Suppress Agrobacterium Overgrowth in Agrobacterium-Mediated Plant Transformation

Agrobacterium overgrowth is a common problem in Agrobacterium-mediated plant transfor-mation. To suppress the Agrobacterium overgrowth, various antibiotics have been used during plant tissue culture steps. The antibiotics are expensive and may adversely affect plant cell differentiation and reduce plant transformation efficiency. The SacB-SacR proteins are toxic to most Agrobacterium tumefaciens strains when they are grown on culture medium sup¬plemented with sucrose. Therefore, SacB-SacR genes can be used as negative selection markers to suppress the overgrowth of Agrobacterium tumefaciens in the plant tissue culture process. We generated a mutant Agrobacterium tumefaciens strain GV2260 (recA-SacB/R) that has the SacB-SacR cassette inserted into the bacterial genome at the recA gene locus. The mutant Agrobacterium strain is sensitive to sucrose but maintains its ability to transform plant cells in both transient and stable transformation assays. We demonstrated that the mutant strain GV2260 (recA-SacB/R) can be inhibited by sucrose that reduces the overgrowth of Agrobacterium and therefore improves the plant transformation efficiency. We employed GV2260 (recA-SacB/R) to generate stable transgenic N. benthamiana plants expressing a CRISPR-Cas9 for knocking out a WRKY transcrip¬tion factor

Photosynthetic Rate and Root Growth Responses to Ascophyllum nodosum Extract–based Biostimulant in Creeping Bentgrass under Heat and Drought Stress

Creeping bentgrass (Agrostis stolonifera) experiences quality decline during summer in the United States transition zone and warmer regions. Various bioproducts have been used to improve creeping bentgrass performance and to mitigate effects of summer stress in the United States transition zone. This 2-year study was carried out to examine if foliar application of seaweed extract (SWE; Ascophyllum nodosum)-based biostimulant Utilize® could enhance creeping bentgrass nitrate reductase (NaR) activity, and root viability under heat and drought stress conditions. The Utilize® was sprayed biweekly on creeping bentgrass foliage at 0, 29, 58, 87, and 116 µL⋅m−2, with application volume of 815 L⋅ha−2. Two weeks after first application, plants were exposed to heat (35/25 °C, day/night) and drought stress (40% to 50% evapotranspiration replacement) conditions for 42 days in an environment-controlled growth chamber. In general, the abiotic stress caused turf quality reduction. Foliar application of Utilize® at 58, 87, and 116 µL⋅m−2 increased turf quality, leaf color ratings, leaf chlorophyll, carotenoid content, and net photosynthetic rate (Pn). Utilize® at 58, 87, and 116 µL⋅m−2 increased NaR activity by 26.5%, 16.3%, and 16.3%, respectively, when compared with the control. Utilize® at 58, 87, and 116 µL⋅m−2 increased root biomass, root length, surface area (SA), and root volume when compared with the control. Utilize® at 58 and 87 µL⋅m−2 improved root viability by 16.3% and 30.9%, respectively, when compared with the control. Our data indicate that the SWE-based biostimulant Utilize® improves nitrogen (N) metabolism and root viability. Utilize® treatment at 58 µL⋅m−2 biweekly can be considered an effective approach for improving creeping bentgrass performance during summer stress

MyBrush: Brushing and Linking with Personal Agency

We extend the popular brushing and linking technique by incorporating personal agency in the interaction. We map existing research related to brushing and linking into a design space that deconstructs the interaction technique into three components: source (what is being brushed), link (the expression of relationship between source and target), and target (what is revealed as related to the source). Using this design space, we created MyBrush, a unified interface that offers personal agency over brushing and linking by giving people the flexibility to configure the source, link, and target of multiple brushes. The results of three focus groups demonstrate that people with different backgrounds leveraged personal agency in different ways, including performing complex tasks and showing links explicitly. We reflect on these results, paving the way for future research on the role of personal agency in information visualization

Heat shock proteins in relation to heat stress tolerance of creeping bentgrass at different N levels.

Heat stress is a primary factor causing summer bentgrass decline. Changes in gene expression at the transcriptional and/or translational level are thought to be a fundamental mechanism in plant response to environmental stresses. Heat stress redirects protein synthesis in higher plants and results in stress protein synthesis, particularly heat shock proteins (HSPs). The goal of this work was to analyze the expression pattern of major HSPs in creeping bentgrass (Agrostis stolonifera L.) during different heat stress periods and to study the influence of nitrogen (N) on the HSP expression patterns. A growth chamber study on 'Penn-A4' creeping bentgrass subjected to 38/28°C day/night for 50 days, was conducted with four nitrate rates (no N-0, low N-2.5, medium N-7.5, and high N-12.5 kg N ha-1) applied biweekly. Visual turfgrass quality (TQ), normalized difference vegetation index (NDVI), photochemical efficiency of photosystem II (Fv/Fm), shoot electrolyte leakage (ShEL), and root viability (RV) were monitored, along with the expression pattern of HSPs. There was no difference in measured parameters between treatments until week seven, except TQ at week five. At week seven, grass at medium N had better TQ, NDVI, and Fv/Fm accompanied by lower ShEL and higher RV, suggesting a major role in improved heat tolerance. All the investigated HSPs (HSP101, HSP90, HSP70, and sHSPs) were up-regulated by heat stress. Their expression patterns indicated cooperation between different HSPs and their roles in bentgrass thermotolerance. In addition, their production seems to be resource dependent. This study could further improve our understanding about how different N levels affect bentgrass thermotolerance

Exogenous Salicylic Acid Optimizes Photosynthesis, Antioxidant Metabolism, and Gene Expression in Perennial Ryegrass Subjected to Salt Stress

Salicylic acid (SA) is a plant growth regulator that can enhance the abiotic stress tolerance of plants; however, the physiological mechanisms are not yet fully understood. The objective of this study was to examine whether exogenous SA could enhance the salt tolerance of perennial ryegrass (Loliumperenne L.; PRG) and investigate the physiological underlying mechanisms. SA was applied to the foliage of PRG at five concentrations (0, 0.25, 0.5, and 1 mM). The SA-treated grass was grown under either control (0 mM NaCl) or salt stress (250 mM NaCl) conditions for 24 d. The SA treatments reduced the leaf electrolyte leakage (EL), malonaldehyde (MDA), and hydrogen peroxide (H2O2) content by 36%, 41%, and 40%, respectively, relative to the control under salt stress as measured at 24 d. The SA treatments also alleviated the decline in the leaf photosynthetic rate (Pn), stomatal conductance (gs), nitrate activity (NR), turfgrass quality (TQ) ratings, and chlorophyll (Chl) content under salt stress. In addition, exogenous SA increased the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD) as well as the expression levels of the Cyt Cu/ZnSOD, FeSOD, APX, CAT, and POD genes under salt stress. The results of this study suggested that the foliar application of SA at 0.25 and 0.5 mM may enhance photosynthesis and antioxidant defense systems and thus improve tolerance to salt stress in perennial ryegrass

Differential responses of CO2 assimilation, carbohydrate allocation and gene expression to NaCl stress in perennial ryegrass with different salt tolerance.

Little is known about the effects of NaCl stress on perennial ryegrass (Lolium perenne L.) photosynthesis and carbohydrate flux. The objective of this study was to understand the carbohydrate metabolism and identify the gene expression affected by salinity stress. Seventy-four days old seedlings of two perennial ryegrass accessions (salt-sensitive 'PI 538976' and salt-tolerant 'Overdrive') were subjected to three levels of salinity stress for 5 days. Turf quality in all tissues (leaves, stems and roots) of both grass accessions negatively and significantly correlated with GFS (Glu+Fru+Suc) content, except for 'Overdrive' stems. Relative growth rate (RGR) in leaves negatively and significantly correlated with GFS content in 'Overdrive' (P0.05 for turf quality). A greater up-regulation in the expression of SPS, SS, SI, 6-SFT gene was observed in 'Overdrive' than 'PI 538976'. A higher level of SPS and SS expression in leaves was found in 'PI 538976' relative to 'Overdrive'. Accumulation of hexoses in roots, stems and leaves can induce a feedback repression to photosynthesis in salt-stressed perennial ryegrass and the salt tolerance may be changed with the carbohydrate allocation in leaves and stems

Exogenous Salicylic Acid Optimizes Photosynthesis, Antioxidant Metabolism, and Gene Expression in Perennial Ryegrass Subjected to Salt Stress

Salicylic acid (SA) is a plant growth regulator that can enhance the abiotic stress tolerance of plants; however, the physiological mechanisms are not yet fully understood. The objective of this study was to examine whether exogenous SA could enhance the salt tolerance of perennial ryegrass (Loliumperenne L.; PRG) and investigate the physiological underlying mechanisms. SA was applied to the foliage of PRG at five concentrations (0, 0.25, 0.5, and 1 mM). The SA-treated grass was grown under either control (0 mM NaCl) or salt stress (250 mM NaCl) conditions for 24 d. The SA treatments reduced the leaf electrolyte leakage (EL), malonaldehyde (MDA), and hydrogen peroxide (H2O2) content by 36%, 41%, and 40%, respectively, relative to the control under salt stress as measured at 24 d. The SA treatments also alleviated the decline in the leaf photosynthetic rate (Pn), stomatal conductance (gs), nitrate activity (NR), turfgrass quality (TQ) ratings, and chlorophyll (Chl) content under salt stress. In addition, exogenous SA increased the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD) as well as the expression levels of the Cyt Cu/ZnSOD, FeSOD, APX, CAT, and POD genes under salt stress. The results of this study suggested that the foliar application of SA at 0.25 and 0.5 mM may enhance photosynthesis and antioxidant defense systems and thus improve tolerance to salt stress in perennial ryegrass