Defenses Against ROS in Crops and Weeds: The Effects of Interference and Herbicides.

The antioxidant defense system acts to maintain the equilibrium between the production of reactive oxygen species (ROS) and the elimination of toxic levels of ROS in plants. Overproduction and accumulation of ROS results in metabolic disorders and can lead to the oxidative destruction of the cell. Several stress factors cause ROS overproduction and trigger oxidative stress in crops and weeds. Recently, the involvement of the antioxidant system in weed interference and herbicide treatment in crops and weeds has been the subject of investigation. In this review, we address ROS production and plant mechanisms of defense, alterations in the antioxidant system at transcriptional and enzymatic levels in crops induced by weed interference, and herbicide exposure in crops and weeds. We also describe the mechanisms of action in herbicides that lead to ROS generation in target plants. Lastly, we discuss the relations between antioxidant systems and weed biology and evolution, as well as the interactive effects of herbicide treatment on these factors.

Soybean Root Growth in Response to Chemical, Physical, and Biological Soil Variations.

Environmental conditions affect crop yield, and water deficit has been highlighted by the negative impact on soybean grain production. Radicial growth in greater volume and depth can be an alternative to minimize losses caused by a lack of water. Therefore, knowledge of how soybean roots behave before the chemical, physical, and biological attributes of the soil can help establish managements that benefit in-depth root growth. The objective was to evaluate the growth of soybean roots in response to chemical, physical, and biological variations in the soil, in different soil locations and depths. Six experiments were conducted in different locations. Soil samples were collected every 5 cm of soil up to 60 cm of soil depth for chemical, physical, and biological analysis. The roots were collected every 5 cm deep up to 45 cm deep from the ground. The six sites presented unsatisfactory values of pH and organic matter, and presented phosphorus, potassium, and calcium at high concentrations in the first centimeters of soil depth. The total porosity of the soil was above 0.50 m3 m-3, but the proportion of the volume of macropores, micropores, and cryptopores resulted in soils with resistance to penetration to the roots. Microbial biomass was higher on the soil surface when compared to deeper soil layers, however, the metabolic quotient was higher in soil depth, showing that microorganisms in depth have low ability to incorporate carbon into microbial biomass. Root growth occurred in a greater proportion in the first centimeters of soil-depth, possibly because the soil attributes that favor the root growth is concentrated on the soil surface.

Soybean Plant Metabolism under Water Deficit and Xenobiotic and Antioxidant Agent Application.

The aim was to evaluate the interactive effects on biochemistry and physiology of soybean plants exposed to simultaneous xenobiotic and water deficit stresses, and the possible attenuation of plant damage by an antioxidant agent. Soybean plants were submitted to eight different soil water potentials, in two experiments (first experiment: -0.96, -0.38, -0.07, -0.02 MPa, and second experiment: -3.09, -1.38, -0.69, -0.14 MPa), xenobiotic, and antioxidant agent applications. Was observed a reduction in water status, gas exchange, photosynthetic pigments, photosystem II quantum yield, and increased leaf temperature in plants under low water availability. Water deficit also induced oxidative stress by the increased production of reactive oxygen species, cellular and molecular damage, and induction of the antioxidant defense metabolism, reduction of gas exchange, water status, and photosynthetic efficiency. The xenobiotic application also caused changes, with deleterious effects more pronounced in low soil water availability, mainly the reactive oxygen species production, consequently the antioxidant activity, and the oxidative damages. This indicates different responses to the combination of stresses. Antioxidant enzyme activity was reduced by the application of the antioxidant agent. Principal Component Analysis showed a relation with the antioxidant agent and reactive oxygen species, which is probably due to signaling function, and with defense antioxidant system, mainly glutathione, represented by thiols.

Biochemical Profile of the Soybean Seed Embryonic Axis and Its Changes during Accelerated Aging.

Seed deterioration is an important topic in plant science, as the majority of cultivated species use seeds as their means of propagation; however, due to its complexity, the process of seed deterioration has not yet been completely elucidated. Three soybean cultivars (BMX Raio, BMX Zeus, and DM 53i54) exposed to four distinct periods of accelerated aging (0, 3, 6 and 9 days) in a fully randomized experimental design. Initially, vigor and germination tests were performed. The activity of superoxide dismutase, catalase, ascorbate peroxidase enzymes, hydrogen peroxide, malonaldehyde, DNA oxidation, macromolecules and mineral content, and Maillard reactions were quantified in the embryonic axis. Results showed that DNA did not suffer degradation or oxidation. In terms of consumption of reserves, only sugars were consumed, while levels of protein, starch, and triglycerides were maintained. The Maillard reaction did show potential as an indicator of buffer capacity of protein to ROS. Additionally, levels of catalase and ascorbate peroxidase decreased during the aging process. Moreover, nutrient analysis showed that a high magnesium level in the cultivar bestowed greater resilience to deterioration, which can indicate a potential function of magnesium in the cell structure via reflex in seed aging through seed respiration.

Physiologic alterations in orthodox seeds due to deterioration processes.

Seed deterioration is a partially elucidated phenomenon that happen during the life of the seed. This review describes the processes that lead to seed deterioration, including loss of seed protection capacity against reactive oxygen species (ROS), damage to the plasma membrane, consumption of reserves, and damage to genetic material. A hypothesis of how seed deterioration occurs was also addressed; in this hypothesis, seed deterioration was divided into three phases. The first is the beginning of deterioration, with a slight reduction of vigor caused by the reactions of reducing sugars with antioxidant enzymes and genetic material. In the second, the cell shows oxidative damages, causing lipid peroxidation, which leads to the leaching of solutes, the formation of malondialdehyde, and, consequently, an increase in damages to genetic material. In the third phase, there is cell collapse with mitochondrial membrane deconstruction and a high accumulation of reactive oxygen species, malondialdehyde, and reducing sugars.

Restrição fotossintética de plantas de soja sob variação de disponibilidade hídrica / Photosynthetic restriction of soybean plants under variation of water availability

O objetivo do trabalho foi caracterizar o metabolismo primário, com ênfase na atividade fotossintética, de plantas de soja sob diferente disponibilidade hídrica. O experimento foi conduzido em câmara de crescimento com plantas jovens de soja cv. BMX Apolo RR, cultivadas sem restrição hídrica até o estádio de seis folhas trifolioladas expandidas e a sétima folha aberta.Foram estudados cinco níveis de disponibilidade hídrica(-0,004, -0,006, -0,026, -0,042 e -0,164MPa) com oito vasos (repetições) por tratamento. Avaliou-se a assimilação líquida de carbono (AL), condutância estomática (gs) e transpiração (E) na sexta folha de uma planta de cada vaso. Foi determinado o potencial da água na folha, fluorescência da clorofila,conteúdo de clorofila (a, b e total), rendimento quântico e caracterizado o crescimento vegetativo. Potenciais da água no solo de -0,026 MPa comprometem a assimilação líquida de carbono de plantas de soja em função da redução da condutância estomática. Os potenciais aplicados não influenciam na quantidade de pigmentos fotossintéticos e no crescimento vegetativo em situações de breve exposição ao estresse.

The aim of the research was to characterize the primary metabolism, with emphasis on photosynthetic activity, of soybean plants under different water availability conditions. The experiment was conducted in growth chamber with young plants of soybean cv. BMX Apolo RR cultivated without water restriction up to the stage of six leaves expanded and the seventh leaf unfolded. Five levels of water availability were studied (-0.004, -0.006, -0.026, -0.042 and -0.164MPa) with eight pots (replications) per treatment. It was evaluated the net carbon assimilation (AL), stomatal conductance (gs) and transpiration (E) of the sixth leaf of one plant per pot. It was determined the water potential leaf, chlorophyll fluorescence, chlorophyll content (a, b and total), quantum yield and it was characterized the vegetative growth. Soil water potential of -0.026 MPa compromises the net carbon assimilation of soybean plants due to reduction of the stomatal resistance. The potentials applied did not influence in the amount of photosynthetic pigments andin the vegetative growth in situations of short exposition to stress.

Índice de área foliar em canola cultivada sob variações de espaçamento e de densidade de semeadura / Leaf area index of canola under varying row spacing and plant density of sowing

O objetivo do presente trabalho foi estimar através de método não-destrutivo o índice de área foliar do híbrido de canola Hyola 61 em variações de espaçamento e densidade de semeadura. O delineamento experimental foi de blocos casualizados com parcelas subdivididas, sendo que nas parcelas foram distribuídos os espaçamentos entre linhas (17, 34, 51 e 68cm) e nas subparcelas as densidades (15, 30, 45 e 60 plantas m-2). Para determinação do comprimento, largura do limbo foliar e da área foliar, bem como estabelecimento de uma correlação entre essas variáveis foram coletadas aleatoriamente 250 folhas. Posteriormente, foram selecionadas aleatoriamente quatro plantas por unidade experimental, que tiveram todas as folhas medidas quanto ao comprimento e largura para estimativa da área foliar e do índice de área foliar. O comprimento do limbo foliar é a variável biométrica com maior correlação com a área foliar. Um comportamento linear entre o adensamento de plantas e o índice de área foliar nos espaçamentos de 34, 51 e 68cm no híbrido Hyola 61 foi observado. O índice de área foliar das plantas foi menor no espaçamento de 17cm, com a densidade de 60 plantas m-2. Para a manutenção do índice de área foliar do híbrido Hyola 61, é recomendável usar o espaçamento de 17cm com a densidade 45 plantas m-2.

The aim of this work was to estimate leaf area index of the canola cultivar 'Hyola 61' under variations of row spacing and density of sowing by a non-destructive method. The experimental design consisted of a split plot with four blocks with row widths of 17, 34, 51 and 68cm and plant populations of 15, 30, 45 and 60m². Two hundred and fifth leaves were collected at random and mesure width (C), length (L) and leaf area (LA) and the parameters were correlated. Also the leaves of four plants of each plot, selected at random, were measured L and C and estimated the leaf area index (LAI). Width leaf was the biometric parameter that shows highest correlation with LA. There is a linear relation between plant density and leaf area index in spacing of 34, 51 and 68cm in 'Hyola 61'. The row width of 17cm and plant population of 60 plants per square meter to reduces the LAI. However, aiming LAI maintenance in Hyola 61 is recommended uses of row width of 17cm and plant population of 45 plants per square meter.

Manejo de videiras sob cultivo protegido / Grapevines management under protected cultivation

O cultivo protegido na cultura da videira apresenta-se como uma alternativa na diminuição da incidência de doenças fúngicas em regiões que apresentam excesso de chuvas no período da maturação. A utilização de cobertura plástica sobre as fileiras de plantas ocasiona modificações no microclima junto às videiras. Essas alterações propiciam condições favoráveis ao crescimento e incremento da produtividade. Todavia, desfavorecem o desenvolvimento de doenças fúngicas, como as podridões de cachos, que atualmente é um dos maiores problemas no controle fitossanitário na "Serra Gaúcha", reduzindo a necessidade de fungicidas. O uso de fungicidas nessas condições merece muita cautela, devido à redução de radiação ultravioleta e ausência de chuvas sobre os cachos, pelo uso da cobertura plástica, que prolonga o período residual dos fungicidas. O maior acúmulo e a persistência são preocupantes, tanto nas uvas destinadas ao consumo in natura, que afeta diretamente o consumidor, quanto nas destinadas à vinificação, em que prejudica a atuação das leveduras na fermentação dos vinhos. De forma geral, a tecnologia de cobrir os vinhedos com filmes plásticos é eficaz no controle de doenças e na redução do uso de fungicidas. Contudo, deve ser considerada como um novo sistema de produção, principalmente por exigir um manejo fitossanitário distinto em relação ao cultivo convencional.

Protected grapevines cultivation is an alternative to decrease incidence of fungal disease in some regions with excess rain during the ripening period. Plastic covering use above rows cause modifications in plant's microclimate. Theses alterations propitiated by protected cultivation can be promotes increase in plant development and yield. Plastic covering is unfavorable for fungal disease development as clusters rot, nowadays, an important problem in healthy handling in Serra Gaúcha Region, reducing the need of sprays. Another point in plastic covering is the necessity of careful fungicides use; due to ultraviolet reduction radiation and rain absence above clusters, which prolongs the fungicide residual period. This higher residual accumulation in grapes is dangerous for consumption in natura, which directly affects the consummator as well as vinification process, interfering in yeast in wine's fermentation. In general, this technology has efficiency in control fungal disease, however, another production system need to be considered, mainly because requires a different management when compared to the conventional production.

Microclima de vinhedos sob cultivo protegido / Microclimate of vineyards under protected cultivation

Alterações microclimáticas em vinhedos, provocadas pelo uso de cobertura plástica, interferem na fisiologia das plantas e na incidência de doenças fúngicas em videiras. Assim, o objetivo deste trabalho foi avaliar a influência da cobertura plástica no microclima de vinhedos, em particular na qualidade da radiação solar. O experimento foi conduzido nos ciclos 2005/06 e 2006/07, em Flores da Cunha, Rio Grande do Sul (RS), em um vinhedo de 'Moscato Giallo' conduzido em "Y", com cobertura plástica impermeável (160µm) sobre 12 fileiras com 35m, deixando-se cinco fileiras sem cobertura (controle). Em ambas as áreas, avaliou-se o microclima quanto à temperatura do ar, umidade relativa do ar, radiação fotossinteticamente ativa e velocidade do vento, próximo ao dossel vegetativo e aos cachos. Medições contínuas foram efetuadas utilizando sensores e sistemas automáticos de aquisição de dados. Alterações na qualidade da radiação solar incidente sobre o dossel vegetativo, no espectro de 300 a 750nm, foram avaliadas por meio de medições durante cinco dias, com espectroradiômetro. A cobertura plástica impermeável à água sobre as fileiras das plantas aumentou a temperatura do ar e diminuiu a radiação fotossinteticamente ativa e a velocidade do vento. A cobertura interferiu na qualidade da radiação solar incidente, principalmente, reduzindo a irradiância na faixa do ultravioleta e a razão entre a radiação nas faixas do vermelho e vermelho-distante.

Microclimate alterations promoted by plastic covering over vineyards interfere in the plant physiology and fungal diseases incidence on grapevines. The aim of this research was to evaluate the influence of the plastic covering on the microclimate of vineyards, in particular on the quality of the incoming solar radiation. The experiment was carried out in 2005/06 and 2006/07 seasons in Flores da Cunha-RS, in a vineyard of Moscato Giallo cultivar shaped in Y, with impermeable plastic (160µm) over 12 rows of 35m length and five rows without covering (control). In both treatments the air temperature and humidity, incoming photosynthetically radiation and wind speed were measured at the level of the canopy and clusters. Continuing measurements were taken through sensors and automatic acquisition systems (datalogger). Influences of the covering on quality of the incoming solar radiation, from 300 to 750nm, were evaluated through a spectroradiometer. The impermeable plastic covering above the plant rows increased the air temperature and decreased the photosynthetically radiation and wind speed. The covering interfered on the quality of the incoming solar radiation, by reducing mainly the irradiance in the ultraviolet band and reducing also the ratio between the irradiance in the red and far-red bands.

Mild temperatures on bud breaking dormancy in peaches / Temperaturas amenas na superação da dormência de pessegueiros

The search for low chill cultivars for peach production in areas with low chill accumulation (temperatures below 7.2°C) has stimulated studies about the higher temperatures effects on low chill cultivars. The objective of this research was to evaluate the influence of mild temperatures on flowering and leafing of 'Turmalina' and 'Ágata' cultivars with low and medium low chilling requirements, respectively. Plants obtained by grafting flower twigs in the autumn, after the grafting, were submitted to chilling treatments (150, 250, 350, 500 and 672 hours) at three temperature levels (5°C, 10°C and 15°C). After the end of the treatments, the plants had been taken to greenhouse (20°C±5°C) and evaluated weekly. The results showed that satisfactory flower and leaf development occur even at temperatures as high as 15°C for a period of 150 hours, in 'Turmalina' peach. Temperatures of 10°C for a period equal or superior to 350 hours promote satisfactory leafing in 'Ágata' peach. Temperatures of 10°C and 15°C cause earlier development of flowers and leaves in both cultivars when compared to 5°C.

A busca por cultivares pessegueiro com baixa necessidade em frio para regiões com pouco acúmulo de frio (temperaturas abaixo de 7,2°C) tem estimulado estudos sobre o efeito de altas temperaturas sobre cultivares de baixa necessidade de frio. O objetivo desta pesquisa foi avaliar a influência de temperaturas amenas na floração e brotação da 'Turmalina' e 'Ágata', duas cultivares com baixa e média necessidade de frio, respectivamente. Plantas obtidas por enxertia no outono foram submetidas a tratamentos de frio (150, 250, 350, 500 e 672 horas) em três níveis de temperatura (5°C, 10°C e 15°C). Após os tratamentos, estas plantas foram colocadas em casa de vegetação a temperatura de 20°C±5°C e avaliadas semanalmente. Conclui-se que temperatura de até 15°C por um período de 150 horas é capaz de resultar em floração e brotação satisfatórias para a cultivar 'Turmalina'. Temperaturas de 10°C por um período igual ou superior a 350 horas promovem brotação satisfatória na cultivar 'Ágata'. Temperaturas de 10°C e 15°C comparadas a 5°C causam antecipação da floração e brotação e ambas cultivares.