Chlorophyll a fluorescence in rice plants exposed of herbicides of group imidazolinone

The objective of this work was to investigate the injuries caused to the photosynthetic apparatus of three types of rice exposed to application of imidazolinone group herbicides. Two experiments were conducted using herbicides Imazethapyr+imazapic and Imazapyr+imazapic, in a split-plot experimental design, and a 3 x 3 factorial, with six replications. The first factor (A) consisted of the herbicide rates 0, 100 e 200 g ha-1 of Imazethapyr+imazapic and 0, 140 e 280 g ha-1 of Imazapyr+imazapic; factor B consisted of type of rice (cv. Puitá Inta CL, sensitive red rice ecotype and red rice ecotype with suspected herbicide tolerance to Imidazolinone). Chlorophyll a fluorescence parameters were evaluated in plants at 30 days after herbicide application, using a portable fluorometer (HandyPEA, Hanstech). The photosynthetic metabolism of cv. Puitá Inta CL was found to tolerate commercial dosages of both herbicides. High sensitivity to the herbicides was observed for the sensitive red rice ecotype, while the photosynthetic apparatus of red rice ecotype with suspected herbicide tolerance showed high tolerance to both herbicides applied at rates higher than the commercial rate. The application of chemical herbicides of the imidazolinone group on rice plants causes changes in the photosynthetic metabolism of plants, detected by evaluating the emission of transient chlorophyll a fluorescence. This method can be useful in helping detect resistance and/or tolerance of red rice plants to herbicides of the imidazolinone group.

Glyphosate as a tool to produce shikimic acid in plants

Oseltamivir phosphate is a potent viral inhibitor produced from shikimic acid extracted from seeds of Ilicium verum, the most important natural source. With the site of action 5-enolpyruvylshikimate-3-phosphate synthase (EPSP), glyphosate is the only compound capable of inhibiting its activity with the consequent accumulation of shikimic acid in plants. Corn and soybean plants were sprayed with reduced rates of glyphosate (0.0 to 230.4 g a.i. ha¹) and shikimic acid content in the dry mass was determined by HPLC 3, 7 and 10 days after application. Results showed shikimic acid accumulation in dry mass with increases of up to 969% in corn and 33,000% on soybeans, with peak concentrations 3 days after treatment (DAT). Industrial feasibility for shikimic acid production, combined with favorable climatic conditions for growing corn and soybean in virtually all over Brazil, favor the use of reduced rates of glyphosate in shikimic acid biosynthesis, with potential for use as an inducer in exploration of alternative sources for production of oseltamivir phosphate with low environmental impact.

Levels of nutrients and grain yield of maize intercropped with signalgrass (Brachiaria) in different arrangements of plants

Competition between maize and signalgrass can economically cripple the intercropping by the reduced yield of maize and dry matter content of the forage. In seeking to define plant arrangements which make this system more efficient, this research was held with the objective of assessing the effects of interference of densities of signalgrass (Urochloa Brizantha) on nutrition and on maize grain yield. Two field experiments were conducted in a randomized block design with four replications. Treatments were arranged similarly in both experiments, in a 2 x 4 factorial design, the first factor being the dose of Nicosulfuron herbicide applied (0 and 8 g ha-1) and the second factor being the forage seeding rates (0, 2, 4 and 6 kg of seeds per hectare). The interference of signalgrass reduced foliar nitrogen, potassium and phosphorus content in maize plants intercropped with the forage. Higher values of grain yield were observed with the reduction of the spacing and the application of the recommended herbicide underdose (8 g ha-1). It was concluded that, regardless of the seeding density of U. Brizantha, reducing the maize seeding inter-rows spacing, combined with the application of an underdose of Nicosulfuron, caused a positive effect by reducing the initial forage growth, resulting in less interference of Urochloa brizantha on nutrient uptake by the maize plants and grain yield of the crop.

Trinexapac-Ethyl and Sulfometuron-Methyl Selectivity to Young Eucalyptus Plants

Trinexapac-ethyl and sulfometuron-methyl are the most widely used ripeners in sugarcane. The application is performed by airborne spraying. Thus, if weather conditions are unfavorable, spray drift to neighboring areas may occur. The objective of this study was to assess the selectivity of the plant growth regulators trinexapac-ethyl and sulfometuron-methyl, used as sugarcane ripeners, to eucalyptus (Eucalyptus urograndis) young plants. The experiment was installed in an eucalyptus commercial yield area, in the municipality of Tambaú, state of São Paulo, Brazil, and arranged in a 2 x 8 factorial design in randomized blocks with four replications. The treatments studied were trinexapac-ethyl and sulfometuron-methyl, sprayed in eight doses, 0; 1.0; 2.5; 5.0; 10; 25; 50 and 100% of the dose used in sugarcane as ripeners (200 g ha-1 of trinexapac-ethyl and 15 g ha-1 of sulfometuron-methyl). Chemical ripeners were applied on eucalyptus plants with 48 cm in height on average; 10.1 branches; 4.5 mm of stem diameter and 44.3 cm of crown diameter, at 46 days after seeding. Trinexapac-ethyl was selective to eucalyptus and stimulated crown diameter growth. At higher doses, sulfometuron-methyl promoted severe noticeable injuries in eucalyptus plants, such as apical bud death. However, during the assessment period the plants recovered and the visual symptoms of phytotoxicity and growth alterations were not observed at 60 days after application. The plant growth regulators trinexapac-ethyl and sulfometuron-methyl were selective to eucalyptus young plants.

Extraction and Simultaneous Determination of Glyphosate, AMPA and Compounds of the Shikimic Acid Pathway in Plants

This study has aimed to develop a method for simultaneous extraction and determination by liquid chromatography and mass spectrometry (LC-MS/MS) of glyphosate, aminomethylphosphonic acid (AMPA), shikimic acid, quinic acid, phenylalanine, tyrosine and tryptophan. For the joint analysis of these compounds the best conditions of ionization in mass spectrometry and for chromatographic separation of the compounds were selected. Calibration curves and linearity ranges were also determined for each compound. Different extraction systems of the compounds were tested from plant tissues collected from sugarcane (Saccharum officinarum) and eucalyptus (Eucalyptus urophylla platiphylla) plants two days after the glyphosate application at the dose of 720 g a.e. ha-1. The plant material was dried in a forced air circulation drying oven and in a lyophilizer, and subsequently the extractions with acidified water (pH 2.5), acetonitrile-water (50:50) [v/v] and methanol-water (50:50) [v/v] were tested. To verify the recovery of the compounds in the plant matrix with acidified water as an extracting solution, the samples were fortified with a solution containing the mixture of the different analytical standards present so that this one presented the same levels of 50 and 100 μg L-1 of each compound. All experiments were conducted with three replicates. The analytical method developed was efficient for compounds quantifications. The extraction from the samples dried in an oven and using acidified water allowed better extraction levels for all compounds. The recovery levels of the compounds in the fortified samples with known amounts of each compound for both plants samples were rather satisfactory.

GLYPHOSATE DRIFT IN EUCALYPTUS PLANTS

ABSTRACTWith the present study we aim to assess the damage caused to Eucalyptus plants exposed to glyphosate drift in different canopy portions. The drift simulation was carried out through application of 1,080 g ha-1 of glyphosate in five canopy portions (0, 25, 50, 75 and 100% of the low branches), in four areas of cultivation. Areas I and II, plants with 0.91 and 2.98 m, and height of canopy drift exposition of 0.30 and 1.0 m, respectively. In areas III and IV both cultivations were 8.15 m high, varying the height of drift exposition between 2.0 and 2.5 m, respectively. At 30 and 480 days after application (DAA), the survival rate was assessed, and at 300 and 480 DAA diameter at breast height (DBH), height, volume and their respective increment were determined. The medium annual increment (MAI) was determined at 480 DAA. Area I, in which the plants were 0.91 m high, we observed that treatment with 100% of the low branches exposed to drift led to stand reduction of the plants around 18.75 and 38.19% at 30 and 480 DAA, respectively. Areas I and II showed reduction in plant growth in height and DBH, wood volume and MAI, to the extent that there was an increase in the portion of canopy exposed to glyphosate drift. However, in areas III and IV, in which 8.15 m height plants were found, no changes were verified for the evaluated characteristics, regardless of the portion of canopy exposed to glyphosate drift.

Changes in Photosynthesis and Oxidative Stress in Wheat Plants Submmited to Herbicides Application

The use of herbicides, even in tolerant crops, can cause stress evidenced by increase phytotoxicity affecting growth and development. The objectives of this study were to evaluate herbicides effect from different mechanisms of action in photosynthetic and oxidative stress parameters, as well visual phytotoxicity and wild radish control in wheat crop, cultivar Quartzo. Two trials were conducted where the first one evaluated the photosynthetic parameters on wheat plants in two seasons collection, following the application of herbicides bentazon, clodinafop, iodosulfuron, metribuzin, metsulfuron and 2,4-D; and the second one evaluated wild radish (Raphanus sativus) control, wheat phytotoxicity and yield due to bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D herbicides application. Photosynthetic rate, stomatal conductance and transpiration were negatively affected by metribuzin, metsulfuron and 2,4-D herbicides at 24 and 120 HAS (hours after spraying) compared to control. Oxidative stress was similar or lower to control, when herbicide was applied and, in general, there was no difference between application times. Lipid peroxidation, catalase activity and phenols were higher in the first collection time. The application of herbicides iodosulfuron and 2,4-D reduces chlorophylls and carotenoids in wheat. Herbicides bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D are selective to wheat, cultivar Quartzo and do not affect wheat yield. 2,4-D, metribuzin and iodosulfuron are more efficient for wild radish control.

Exploring Herbicidal Potential of Aqueous Extracts of Some Herbaceous Plants Against Parthenium Weed

To assess the phytotoxic potential of Achyranthes aspera, Alternanthera philoxeroides, Datura metel and Rumex dentatus against Parthenium hysterophorus, 5% (w/v on dry weight basis) aqueous extracts from root, stem, leaf, flower and whole plant were tested through a Petri plate-based germination and pot-cultured seedling bioassays. Achyranthes aspera and A. philoxeroides inhibited parthenium weed germination more than extracts from other species. Whole plant, leaf and fruit extracts of A. aspera reduced the germination percentage (5%); leaf extract from A. philoxeroides caused lower germination index (0.4), higher mean germination time (14 d) and longer time to 50% germination (13.5 d) of parthenium weed. In the foliar spray bioassay, A. aspera reduced parthenium weed shoot growth more than the other species whereas R. dentatus caused more reduction in root growth. Whole plant extract from A. aspera caused maximum reduction in parthenium weed seedling vigor index (98%) and seedling biomass (96%). The aqueous extracts of A. aspera and A. philoxeroides contained higher concentrations of phenolics viz. gallic (16.9 mg L-1), caffeic (7.4 mg L-1), chromatotropic (63.8 mg L-1), p-coumaric (10.5 mg L-1), m-coumaric (3.1 mg L-1), syringic (9.21 mg L-1) and 4 hydroxy-3-methoxy benzoic (118.6 mg L-1) acids compared with extracts of the other two species tested.

Physiological and Genetic Bases of the Circadian Clock in Plants and Their Relationship with Herbicides Efficacy

In order to adapt to daily environmental changes, especially in relation to light availability, many organisms, such as plants, developed a vital mechanism that controls time-dependent biological events: the circadian clock. The circadian clock is responsible for predicting the changes that occur in the period of approximately 24 hours, preparing the plants for the following phases of the cycle. Some of these adaptations can influence the response of weeds to the herbicide application. Thus, the objectives of this review are to describe the physiological and genetic mechanisms of the circadian clock in plants, as well as to demonstrate the relationship of this phenomenon with the effectiveness of herbicides for weed control. Relationships are described between the circadian clock and the time of application of herbicides, leaf angle and herbicide interception, as well as photosynthetic activity in response to the circadian clock and herbicide efficiency. Further, it is discussed the role of phytochrome B (phyB) in the sensitivity of plants to glyphosate herbicide. The greater understanding of the circadian clock in plants is essential to achieve greater efficiency of herbicides and hence greater control of weeds and higher crop yields.

Comparative uptake and metabolism of 2-[14C]-2,4-dichlorophenoxyacetic acid in callus cultures of monocot (Dioscorea spp.) and dicot (Nicotiana tabacum L.) plants

(Comparative uptake and metabolism of 2-[14C]-2,4-dichlorophenoxyacetic acid in callus cultures of monocot (Dioscorea spp.) and dicot (Nicotiana tabacum L.) plants). The uptake and metabolism of 2-[14C]-2,4-dichlorophenoxyacetic acid (2,4-D) were investigated in leaf calluses of Nicotiana tabacum, tuber calluses of Dioscorea opposita and calluses derived from zygotic embryos, leaves and petioles of Dioscorea composita. Striking similarities were evident in the patterns of 2,4-D metabolites and their chemical characteristics in the three callus types of D. composita compared, but significant differences were detected among the patterns of rnetabolites in the three species studied. Preliminary investigations on the stability of various metabolites (separated using TLC) by hydrolysis showed that sugar esters appeared to be the major metabolites in tobacco whilst in yams (D. opposita) glycosides were shown to be the main ones, which indicated a similarity between plants of Gramineae and Dioscoreaceae in terms of 2,4-D metabolism. Release of 2,4-D from tobacco callus cells upon their transfer to 2,4-D-free medium was detected and the implications of this are discussed in relation to the cultural conditions necessary to induce morphogenesis in vitro.

Respuestas morfológicas y anatómicas de Tessaria absinthioides (Hook. et Arn.) DC. a la salinidad

T. absinthioides, Inuleae, Compositae, is a weedy species that is spreading in the irrigation area of the Colorado River, Argentina. This species can be found in normal and saline soils. Morphological and anatomical variables were measured with two salts, sodium chloride and sodium sulfate, with three levels of osmotic potential -0.4, -0.8 and -1.5 MPa, in hydroponic culture, using Hoagland solution as the cultivation media. The total diameter of the roots of plants growing in Na2SO4 and NaCl increased when the osmotic potential was -0.4 MPa. In plants growing in NaCl this may have resulted from the increase in the size of the cortical cells and in plants growing in Na2SO4, the diameter increased may be due to an increase in the cambial activity. The number and length of shoot internodes decreased with increasing salinity, even though this was not statistically significant. In comparison to the control, the total diameter of the shoot increased at -0.4 MPa and decreased with the reduction of the osmotic potential. In comparison to the control, the length of the leaves decreased at -0.4 MPa and the leaves width increased at the same concentration. The palisade parenchyma appeared less developed in saline conditions. In comparison to the control, the number of hairs increased at -0.4 MPa. T. absinthioides acts as a semihalophytic species, according to the salt ranks it tolerates. The mechanisms of adaptation to saline conditions are succulence in root and stunted growth if the salt in the media is NaCl, and the production of haloxeromorphic characters if the salt in the media is Na2 SO4

Effects of using different host plants on the detected biodiversity of arbuscular mycorrhizal fungi from an agroecosystem

The influence of peanut (Arachis hypogaea L.), sorghum (Sorghum bicolor (L.) Moench) and maize (Zea mays L.) on the development and diversity of arbuscular mycorrhizal fungi (AMF) from an agrosystem was investigated. Soil collected from an agricultural field where maize had been grown was inserted into sowing holes, under the seeds of peanut, sorghum and maize those were subsequently grown in sterilised quartz sand separately in plastic boxes for five months. After this period, collections of roots and rhizospheric soil were made to evaluate the percentages of root colonization (RC), number of spores (NS) and species of AMF. Peanut showed the highest average values for RC and NS: 24.5% and 547.8/100 g of soil, respectively. Maize had an average RC of 19.7% and 415.2 spores/100g soil. Sorghum showed the lowest values: 15.9% for average RC and 349.8 spores/100 g soil. A total of fourteen species of AMF were identified. Seven species were identified from peanut rhizospheres, Entrophospora colombiana being the most abundant and frequent. In sorghum rhizospheres, twelve species were found, Glomus geosporum was the dominant taxon in terms of number of spores and frequency. Ten species were detected in maize with Acaulospora longula being the most abundant and the most frequent. It was observed that peanut was the best plant for promoting the sporulation of AMF, while sorghum favoured the establishment of most AMF species, followed by maize.

Community structure of vascular plants in treefall gaps and fire-disturbed habitats in the Atlantic rainforest, southern Bahia, Brazil

The effects of disturbances on plant community structure in tropical forests have been widely investigated. However, a majority of these studies examined only woody species, principally trees, whereas the effects of disturbances on the whole assemblage of vascular plants remain largely unexplored. At the present study, all vascular plants < 5m tall were surveyed in four habitats: natural treefall gaps, burned forest, and their adjacent understorey. The burned area differed from the other habitats in terms of species composition. However, species richness and plant density did not differ between burned area and the adjacent understorey, which is in accordance to the succession model that predict a rapid recovery of species richness, but with a different species composition in areas under moderate disturbance. The treefall gaps and the two areas of understorey did not differ among themselves in terms of the number of individuals, number of species, nor in species composition. The absence of differences between the vegetation in treefall gaps and in understorey areas seems to be in agreement with the current idea that the species present in treefall gaps are directly related to the vegetation composition before gap formation. Only minimal differences were observed between the analyses that considered only tree species and those that considered all growth habits. This suggests that the same processes acting on tree species (the best studied group of plants in tropical forests) are also acting on the whole assemblage of vascular plants in these communities.

Synecological comparisons sustained by ecophysiological fingerprinting of intrinsic photosynthetic capacity of plants as assessed by measurements of light response curves

In some literature variations in photosynthetic rates are considered to be of little relevance for individual fitness. This depends among other things on how one defines fitness, i.e. if one takes strictly Darwinian fitness as seed production or if one needs to evaluate particular traits and consider plant establishment. It also matters if one takes the Darwinian "organism individual" as the central entity in evolution ("individual fitness") or the "species individual" in a modified "Structure of Evolutionary Theory" sensu Stephen Jay Gould. A phenotypically expressed trait like photosynthetic rate, even if intra- and interspecific differences may be small, can matter in habitat performance and niche acquisition. Light dependence curves (LCs) of photosynthetic rates are now readily measured under field conditions using miniaturized equipment of pulse amplitude modulated fluorometers. In contrast to actual momentary measurements of quantum yield of photosynthesis under actually prevailing ambient conditions, LC measurements reflect the expressed intrinsic capacity of photosynthesis. In this review we explore the power of LC measurements yielding cardinal points such as maximum apparent electron transport rate of photosystem II (ETRmax) and saturating photosynthetically active radiation (PARsat) in making intra- and interspecific comparisons of plant performance and synecological fingerprinting in ecophysiological studies across species, sites, habitats and ecosystems.