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Salinity is a limiting factor for growth and development, since it affects several physiological processes in plants. This trial aimed to assess the levels of photosynthetic pigments, betacyanins, lipid peroxidation and activity of antioxidant enzymes in Alternanthera philoxeroides under salt stress. Plants originated from an in vitro culture were acclimatized and irrigated with sodium chloride (0, 200 and 400 mM) for 30 d. The experimental design was completely randomized with a 3×2 factorial arrangement of treatments: three concentrations of NaCl and two plant tissues (stems and leaves). The experimental data was subjected to an analysis of variance and means where compared using Tukey test (p⩽0.05). The levels of chlorophylls a, chlorophylls b and total carotenoids presented similar responses, decreasing their values according to salt concentrations, while the chlorophyll a/b ratio of the plants that were submitted to the highest salt concentration presented a significant increase when compared to the control. Higher levels of betacyanin were observed on stems, when compared to the leaves, in the highest salt concentrations. On the leaves, there was a significant increase of lipid peroxidation and superoxide dismutase activity, whereas roots showed an increase of the enzymes catalase and ascorbate peroxidase. Salt stress caused greater degradation in the photosynthetic pigments, increment of betacyanin synthesis in stems, and damage to the cell membranes of the leaves. However, the increase of antioxidant enzymes activity stimulated the protective system against oxidative stress. It is concluded that Alternanthera philoxeroides (Mart.) Griseb. plants present reduction in levels of photosynthetic pigments, increased synthesis of betacyanins and increased activity of antioxidant enzymes in leaves and roots when exposed to salt stress. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effect of agents inducing water and saline stress on the seed germination and early growth and antioxidant activity in sunflower seedlings. Sunflower seeds, cv. M735, were germinated on moistened paper in solutions with osmotic potentials of 0.0,-0.2, -0.4 and -0.8 MPa induced by PEG 6000 and NaCl. The germination test was conducted with four samples of 100 seeds and four replicates per treatment, in a germination chamber at 25 °C without light. We evaluated the final percentage and speed of germination index, and the initial growth and activity of antioxidant enzymes in sunflower seedlings. Water stress induced by PEG 6000 increased the percentage of seeds germinated in the potential of -0.2 MPa, on the other hand, for NaCl in the potential of -0.8 MPa, there was a significant reduction. For this same potential, there was also a reduction in the rate of seed germination speed index in both conditioning agents. For the parameters of growth, shoot length decreased linearly with increasing concentrations of PEG 6000 and NaCl. As for the dry mass of leaves and roots and root length, this effect was more significant only in the potential of -0.8 MPa. The enzymes SOD, APX and CAT activity tended to be lower in seedlings originating from seeds in PEG 6000. In the presence of NaCl, the activity of SOD in the leaves increased significantly in the three tested for potential witnesses. For APX and CAT increase was observed at potentials of -0.2 and -0.4 MPa. In the roots there was no significant difference. An analysis of the evaluated parameters indicates that sunflower cv M735, under the conditions tested, showed tolerance to drought stress and salt until the potential of -0.4 MPa. [ABSTRACT FROM AUTHOR]

Rice is essential to feed the world's population, being the most important staple food in several countries. Crop production has been directly impacted by climate change. Plants can mitigate an increase in atmospheric CO2 concentration through photosynthetic conversion into carbohydrates. However, the potential for this conversion and plant responses to climate change remain unclear. The study was conducted from the cultivation of plants in open-top chambers (OTCs) with two concentrations of CO2, 400 ppm (ambient – a[CO2]) and 700 ppm (enhanced – e[CO2])). We used rice plants of the cultivar IRGA 424 RI. Evaluations occurred in the vegetative (V5 and V11) and reproductive (R2 and R7) stages. As for gas exchange, plants grown under e[CO2] showed increased net CO2 assimilation rate, greater water use efficiency, and higher intercellular CO2 concentration. On the other hand, the lowest values for stomatal conductance, chlorophyll index, nitrogen balance index, percentage of nitrogen in the leaves, and thousand-grain weight were found for this treatment. In addition, there was an increase in the activity of the glutamine synthetase and nitrate reductase enzymes in leaves and roots under e[CO2], as well as a higher content of nitrate, starch, water-soluble polysaccharides and total soluble sugars in leaves in the first evaluated phenological stage. These results showed us that the reductions in chlorophyll levels added to the stimulation of the photosynthetic machinery elevated the nutritional demand. Due to these impacts, nitrogen and carbon metabolism were reduced, negatively reflecting on the yield components of rice plants. [ABSTRACT FROM AUTHOR]

Seed priming with salicylic acid (SA) has been described as a method with potential to improve seed germination under unfavorable conditions. The present study aimed to evaluate the ability of seed priming with SA to attenuate the impact of water restriction during germination and early seedling growth of tomato. Seeds were subjected to different concentrations of SA (0, 25 and 50 µM) and sowed on substrates at different percentages of the water holding capacity (20, 30, 40 and 100%). The following variables were evaluated: germination, first count of germination, germination speed index, shoots/root length and dry mass, superoxide dismutase, ascorbate peroxidase and catalase activities, contents of hydrogen peroxide and of malondialdehyde. Water restriction significantly decreased the variables related to germination and seedling performance. Despite increasing germination speed and seedling development when combined with well-irrigated conditions, priming with SA negatively impacted those characteristics under water deficit conditions. That was through increases in superoxide dismutase activity and H2O2 accumulation. Thus, it was concluded that seed priming with SA does not improve tomato seed germination and early seedling growth under water deficit. [ABSTRACT FROM AUTHOR]

The objectives of this study were to estimate the residual and half-life of [imazapic + imazapyr] and to infer on the impact of these residuals over time. The first experiment comprised the application of [imazapic + imazapyr] to Clearfield® rice. On the following summer cropping season (365 days later), undeformed soil samples 0-5 cm depth were collected and seeds of six species or varieties were sown as bioindicators of residuals (experiment 2), being assessed plant height and dry mass 20 days after emergence start. The third experiment comprised the cultivation of the same species submitted to ten increasing herbicide doses (0-280 g ha−1) to establish standard response curves, also assessing plant height and dry mass 20 days after emergence start. About 2.1-5.8% of the applied imazapic remains in soil after one year, for the label doses. Imazapyr was considered to be at negligible doses as its half-life is short, and less than 0.0000001% of the applied dose is expected to be in soil 365 days later. The expected imazapic half-life in lowland areas of Southern Brazil is longer than for dryland, being estimated as between 63 and 77 days (95% confidence interval), contrasting to the 60 days half-life previously estimated for dryland soils. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effect of different salt concentrations on the germination, initial biomass and oxidative stress of four cowpea genotypes, commonly grown in the São José do Norte region, RS. The seeds of the genotypes Amendoim, Mosqueado, Baio and Preto were planted in rolls of "germitest" paper, soaked in a solution of sodium chloride at concentrations of zero, 50, 100, 150 and 200 mM and placed to germinate at a constant temperature of 25 oC. Variables studied were: germination, first count, length and dry mass of the shoots and roots of seedlings, lipid peroxidation and the specific activity of superoxide dismutase, ascorbate peroxidase and catalase. Increasing salt concentration adversely affected seed germination and also the first count of the four cowpea genotypes for the 100 mM salt treatment. Joint analysis of the regression curves for the growth parameters showed the same tendency for the four genotypes, with a significant growth reduction as salt stress increased. Stress effects were also evident from increased lipid peroxidation in the 200 mM salt treatment, followed by reduced enzyme antioxidant activity, since in the intermediate salt concentrations, the antioxidant enzymes efficiently eliminated reactive oxygen species (ROS), preventing oxidative stress. These results indicate that, at intermediate doses of salt, there was good initial development of the four cowpea genotypes and the best response was observed in the Amendoim genotype. [ABSTRACT FROM AUTHOR]

Previous research demonstrated that the interval between defoliation treatments based on the leaf stage is a promising tool for the management of annual ryegrass (Lolium multiflorum L.) pasture. The use of this tool, which is based on the physiological status of the plant, could also benefit the seed production. We assessed the effects of the time of defoliation based on leaf stage on seed yield and quality of annual ryegrass cut to three residual stubble heights (RSH) (50%, 25% and 0% of plant height pre-defoliation) and a second defoliation applied to certain treatments based on the leaf stage of the plant regrowth (two or three leaves per tiller). Higher defoliation intensities (lower RSH) increased the amount of harvested forage to 4.0 t DM ha-1. Moderate defoliation (50%) undertaken at the 3-leaf stage combined with intense defoliation (25% and 0%) at the 2-leaf stage resulted in the highest seed yields (1.8 t ha-1). However, lower RSH reduced mean seed weight and physiological seed quality, which was also associated with lower seed starch and protein content. Accelerated ageing (AA) tests were used to compare seed vigour between treatments. A second defoliation at the 3-leaf stage plus intense defoliation (RSH 0%) resulted in seed lots with a high rate of lipid peroxidation after the AA test, followed by lower catalase activity, germination, and seedling growth. The combination of a second defoliation at the 3-leaf stage and the retention of higher RSH (50%) promoted a greater proportion of leaf blades in the stubble, with a strong positive correlation with seed production and vigour. Antioxidant enzyme activity after the AA test is an important marker of annual ryegrass seed quality. [ABSTRACT FROM AUTHOR]

Rice is a crop that presents sensitivity to cold, especially in the germination phase, which leads to high economic losses. Alternative management forms are essential to increase tolerance to low temperatures, and seed priming represents a promising tool. The objective of this study was to investigate the priming effect of the aqueous extract of carrot roots on rice seeds to increase tolerance to low temperatures during germination. Seeds from cultivars BRS Querência (cold-susceptible) and Brilhante (cold-tolerant) were soaked for 24 h in concentrations of 0, 25, 50, and 100% carrot extract, sown on germitest paper and conditioned in BOD for 21 days at 15 °C. As a control, the seeds soaked in water were also germinated at 25 °C. They were evaluated for germination, first germination count, and germination speed index to calculate the stress indices: tolerance index, susceptibility index, and harmonic mean. They were also evaluated for the length and dry mass of shoot and root. The results showed that the rice seeds conditioning in carrot extract effectively reduces the damage caused by cold, significantly increasing the germination speed and the percentage of final germination and the growth evaluations, more expressive at 100% concentration. The stress indexes are efficient in estimating the tolerance of the cultivars and the effect of the different conditions in low-temperature conditions, highlighting the superiority of the Brilhante cultivar. [ABSTRACT FROM AUTHOR]

Tomato is a Solanaceae of great importance for the agribusiness being the vegetable-fruit more consumed in the world. Climate change, such as increased atmospheric concentration of CO2, has raised concern about food security by direct influence in the food production. The objective of this work was to evaluate the effects of atmospheric CO2 concentration on morph-physiological characteristics and tomato production. For this, plants of the cultivar Micro-Tom were cultivated under 400 or 700 μmol mol-1 of atmospheric CO2 and evaluated for growth, physiological responses, yield and fruit quality. Results showed that the elevation of CO2 concentration from 400 to 700 μmol mol-1 caused morpho-physiological changes in the tomato plants. In plants grown at 700 μmol mol-1 of CO2 occurred reduction in chlorophylls concentration, and increase in the concentration of flavonoids, leaf area, leaf dry matter, Dickson quality index, fruit size and weight, and fruit yield per plant. In regarding to fruit color, there was increase of the a* and reduction of the chroma in response to the increase in CO2 concentration. In conclusion, the increase in the atmospheric CO2 concentration resulted in changes in physiological processes, gain in leaf area, as well as, increase in fruit production and its visual quality. [ABSTRACT FROM AUTHOR]

The increase in the concentration of atmospheric CO2 is one of the main environmental variables that can affect the production of cultivated plants. The objective of this study was to evaluate the effects of increase the atmospheric CO2 concentration on morphological and grain yield characteristics of wheat. For this, wheat plants of cultivar Marfim were cultivated under two CO2 concentrations (400 or 700 μmol mol-1). The variables evaluated were: gas exchange, morphological alteration and grain yield components. The increases in the CO2 concentration significantly altered the gas exchange parameters, increased anthocyanin index, plant height, leaf area, dry mass of leaves and roots. In regarding to yield, plants at 700 μmol mol-1 produced high number of grains per ear, high weight of thousand grains, high hectoliter weight (PH) and total production. Thus, the increase in atmospheric CO2 concentration influenced the agronomic performance of wheat through physiological alteration, biomass gain and increase in the grains yield. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) improve plant ability to uptake P and tolerate heavy metals. This study aimed to evaluate the effect of available P and the inoculation of Rhizophagus clarus in a Cu-contaminated soil ( i ) on the activity of acid phosphatases (soil and plant), the presence of glomalin, and ( ii ) in the biochemical and physiological status of Mucuna cinereum . A Typic Hapludalf soil artificially contaminated by adding 60 mg kg −1 Cu was used in a 3 × 2 factorial design with three replicates. Treatments consisted of three P levels: 0, 40, and 100 mg kg −1 P. Each P treatment level was inoculated (+AMF)/non-inoculated (−AMF) with 200 spores of R. clarus per pot, and plants grown for 45 days. The addition of at least 40 mg kg −1 P and the inoculation of plants with R. clarus proved to be efficient to reduce Cu phytotoxicity and increase dry matter yield. Mycorrhization and phosphate fertilization reduced the activity of enzymes regulating oxidative stress (SOD and POD), and altered the chlorophyll a fluorescence parameters, due to the lower stress caused by available Cu. These results suggest a synergism between the application of P and the inoculation with R. clarus , favoring the growth of M. cinereum in a Cu-contaminated soil. This study shows that AMF inoculation represents an interesting alternative to P fertilization to improve plant development when exposed to excess Cu. [ABSTRACT FROM AUTHOR]

The silicon (Si) reduced tan spot ( Pyrenophora tritici-repentis ) severity up to 40%, through both biochemical defense mechanisms and histo-cytological defense responses. The activities of enzymes involved in plant defense system such as superoxide dismutase, peroxidase and chitinase showed greater activity in inoculated plants supplied with Si. Histo-cytological analysis indicated that Si potentiated the accumulation of hydrogen peroxide in the beginning of infection process. Together, these defense mechanisms resulted in the reduction of cell death at the infection sites in plants supplied with Si, which in turn showed lower disease severity. Si appears to be a promising alternative control measure for use in integrated management of tan spot. [ABSTRACT FROM AUTHOR]

In high-yield irrigated rice systems, options for legume cover crops with the capacity for biological nitrogen (N) fixation in the period between harvest have been sought. However, options are limited due to excess water and low oxygen level in the soil. The persian clover (Trifolium resupinatum) is an exception as it is a promising species due to its adaptation to waterlogged soils. Thus, the objective of this work was to evaluate accumulated nitrogen in the legume, soil mineral and microbial N levels and the response of a rice hybrid established in succession to persian clover during four growing seasons in subtropical conditions in southern Brazil. The field experiment was carried out during four crop seasons in a 2 × 4 factorial, with two conditions of soil cover, fallow and legume (persian clover) under four levels of N (0, 60, 120 and 180 kg N ha−1). It was observed that the cultivation of Persian clover increased the availability of mineral and microbial N in the soil by 35% and 6.5%, respectively. There was a 14.1% reduction in the optimal nitrogen rate in the rice hybrid. The grain yield of rice grains using persian clover in winter is 7.8% higher in relation to fallow, with the greatest difference between clover and fallow at the lowest N rates (0 e 60 kg ha−1). Thus, persian clover is a promising legume to be used in the period between harvest in hydromorphic soils cultivated with irrigated rice in subtropical conditions. [Display omitted] • Persian clover increase 35% soil mineral nitrogen. • Use of legume (Persian clover) reduces nitrogen fertilization by 14.1%. • Persian clover legume increases rice grain yield by 7.8%. [ABSTRACT FROM AUTHOR]

Plants in their natural environment are subject to adverse conditions, and the stress periods can be short or long. Some species develop mechanisms that make them bear the adverse conditions, allowing their survival. The aim of this study was to evaluate the anatomic and physiological responses in the initial development of Sibipiruna plants submitted to hypoxia. Plants with three to four leaves fully expanded were subjected to three treatments: plants without flooding, flooded on roots and totally flooded. Evaluations were carried out in the starch, total soluble sugars and reducing sugars levels in the leaves and roots collected every five days, for 30 days. Anatomical characteristics were evaluated 15 days after the beginning of each treatment. The largest reduction in starch level in leaves and in roots was observed in plants completely flooded. For total soluble sugars and reducing sugars were observed behavior similar to that achieved in starch However, the plants which had flooded roots, in some periods of assessment, had levels, mainly in the roots, higher than the plants without flooding. These plants also showed higher stomatal density than the other treatments. For the thickness of the cortex and the cylinder vascular roots, a reduction was observed for the flooded treatment, which completely flooded plants had a higher apoplastic barrier imposed by thickening in phi, which is characterized by the formation of septa in cells near the endodermis. [ABSTRACT FROM AUTHOR]

Rice plants cultivated under 700 ppm atmospheric CO 2 concentration presented a reduction in the progress and severity of the brown spot disease (Bipolaris oryzae), through the enhancement of biochemical defense mechanisms. Plants exposed to 700 ppm of CO 2 had higher activity of the enzymes superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, polyphenoloxidase and chitinase, and increased phenolic compounds and lignin concentration, independent of the rice cultivar. Therefore, the lower severity values of the disease were related to changes in the development of the lesions as a result of the defense responses, which were stimulated in the rice plants by the increase of CO 2 concentration. • This study demonstrated that increase of atmospheric CO 2 improves rice resistance to brown spot. • Rice under enhanced atmospheric CO 2 concentration have a better attenuation of the oxidative damages. • Rice under enhanced atmospheric CO 2 concentration have the reduction on the severity of the brown spot. • Rice exposed to 700 ppm of CO 2 had higher activity of antioxidant enzymes. • Rice exposed to 700 ppm of CO 2 had higher concentration of phenolic compounds and lignin content. [ABSTRACT FROM AUTHOR]