Leaf thermotolerance of Hevea brasiliensis clones: intra- versus interclonal variation and relationships with other functional traits.

Land surface temperature is predicted to increase by 0.2 °C per decade due to climate change, although with considerable regional variability, and heatwaves are predicted to increase markedly in the future. These changes will affect where crops can be grown in the future. Understanding the thermal limits of plant physiological functioning and how flexible such limits are is thus important. Here, we report on the measurements of a core foliar thermotolerance trait, T50, defined as the temperature at which the maximum quantum yield (Fv/Fm) of photosystem II declines by 50%, across nine different Malaysian Hevea brasiliensis clones. We explore the relative importance of interclonal versus intraclonal variation in T50 as well as its association with leaf and hydraulic traits. We find very low variation in T50 within individual clones (mean intraclonal coefficient of variation (CoV) of 1.26%) and little variation across clones (interclonal CoV of 2.1%). The interclonal variation in T50 was lower than for all other functional traits considered. The T50 was negatively related to leaf mass per area and leaf dry matter content, but it was not related to hydraulic traits such as embolism resistance (P50) or hydraulic safety margins (HSM50). The range of T50 observed (42.9-46.2 °C) is well above the current maximum air temperatures Tmax,obs (T50 - Tmax,obs >5.8 °C), suggesting that H. brasiliensis is likely thermally safe in this south-east Asian region of Malaysia.

Photosynthetic acclamatory response of Panicum antidotale Retz. populations to root zone desiccation stress

Abstract Growth of plants is severely reduced due to water stress by affecting photosynthesis including photosystem II (PSII) activity and electron transport. This study emphasised on comparative and priority targeted changes in PSII activity due to progressive drought in seven populations of Panicum antidotale (P. antidotale) collected from Cholistan Desert and non-Cholistan regions. Tillers of equal growth of seven populations of P. antidotale grown in plastic pots filled with soil were subjected progressive drought by withholding water irrigation for three weeks. Progressive drought reduced the soil moisture content, leaf relative water content, photosynthetic pigments and fresh and dry biomass of shoots in all seven populations. Populations from Dingarh Fort, Dingarh Grassland and Haiderwali had higher growth than those of other populations. Cholistani populations especially in Dingarh Grassland and Haiderwali had greater ability of osmotic adjustment as reflected by osmotic potential and greater accumulation of total soluble proteins. Maximum H2O2 under water stress was observed in populations from Muzaffargarh and Khanewal but these were intermediate in MDA content. Under water stress, populations from Muzaffargarh and Dingarh Fort had greater K+ accumulation in their leaves. During progressive drought, non-Cholistani populations showed complete leaf rolling after 23 days of drought, and these populations could not withstand with more water stress condition while Cholistani populations tolerated more water stress condition for 31 days. Moreover, progressive drought caused PSII damages after 19 days and it became severe after 23 days in non-Cholistani populations of P. antidotale than in Cholistani populations.

Resumo O crescimento das plantas é severamente reduzido devido ao estresse hídrico, afetando a fotossíntese, incluindo a atividade do fotossistema II (PSII) e o transporte de elétrons. Este estudo enfatizou as mudanças comparativas e prioritárias na atividade do PSII devido à seca progressiva em sete populações de Panicum antidotale (P. antidotale) coletadas no Deserto do Cholistão e regiões fora do Cholistão. Perfilhos de igual crescimento de sete populações de P. antidotale cultivadas em vasos de plástico cheios de solo foram submetidos à seca progressiva, retendo a irrigação com água por três semanas. A seca progressiva reduziu o teor de umidade do solo, teor de água relativo nas folhas, pigmentos fotossintéticos e biomassa fresca e seca dos brotos em todas as sete populações. Populações de Dingarh Fort, Dingarh Grassland e Haiderwali tiveram maior crescimento do que as de outras populações. As populações de Cholistani, especialmente em Dingarh Grassland e Haiderwali, apresentaram maior capacidade de ajuste osmótico, refletido pelo potencial osmótico e maior acúmulo de proteínas solúveis totais. H2O2 máximo sob estresse hídrico foi observado em populações de Muzaffargarh e Khanewal, mas estas foram intermediárias no conteúdo de MDA. Sob estresse hídrico, as populações de Muzaffargarh e Dingarh Fort tiveram maior acúmulo de K+ em suas folhas. Durante a seca progressiva, as populações não cholistanesas mostraram rolagem completa das folhas após 23 dias de seca, e essas populações não conseguiram suportar mais condições de estresse hídrico, enquanto as populações cholistani toleraram mais condições de estresse hídrico por 31 dias. Além disso, a seca progressiva causou danos ao PSII após 19 dias e tornou-se severa após 23 dias em populações não cholistanesas de P. antidotale do que em populações cholistanesas.

Photosynthetic acclamatory response of Panicum antidotale Retz. populations to root zone desiccation stress / Reação fotossintética aclamatória de Panicum antidotale Retz. populações submetidas ao estresse da dessecação da zona radicular

Abstract Growth of plants is severely reduced due to water stress by affecting photosynthesis including photosystem II (PSII) activity and electron transport. This study emphasised on comparative and priority targeted changes in PSII activity due to progressive drought in seven populations of Panicum antidotale (P. antidotale) collected from Cholistan Desert and non-Cholistan regions. Tillers of equal growth of seven populations of P. antidotale grown in plastic pots filled with soil were subjected progressive drought by withholding water irrigation for three weeks. Progressive drought reduced the soil moisture content, leaf relative water content, photosynthetic pigments and fresh and dry biomass of shoots in all seven populations. Populations from Dingarh Fort, Dingarh Grassland and Haiderwali had higher growth than those of other populations. Cholistani populations especially in Dingarh Grassland and Haiderwali had greater ability of osmotic adjustment as reflected by osmotic potential and greater accumulation of total soluble proteins. Maximum H2O2 under water stress was observed in populations from Muzaffargarh and Khanewal but these were intermediate in MDA content. Under water stress, populations from Muzaffargarh and Dingarh Fort had greater K+ accumulation in their leaves. During progressive drought, non-Cholistani populations showed complete leaf rolling after 23 days of drought, and these populations could not withstand with more water stress condition while Cholistani populations tolerated more water stress condition for 31 days. Moreover, progressive drought caused PSII damages after 19 days and it became severe after 23 days in non-Cholistani populations of P. antidotale than in Cholistani populations.

Resumo O crescimento das plantas é severamente reduzido devido ao estresse hídrico, afetando a fotossíntese, incluindo a atividade do fotossistema II (PSII) e o transporte de elétrons. Este estudo enfatizou as mudanças comparativas e prioritárias na atividade do PSII devido à seca progressiva em sete populações de Panicum antidotale (P. antidotale) coletadas no Deserto do Cholistão e regiões fora do Cholistão. Perfilhos de igual crescimento de sete populações de P. antidotale cultivadas em vasos de plástico cheios de solo foram submetidos à seca progressiva, retendo a irrigação com água por três semanas. A seca progressiva reduziu o teor de umidade do solo, teor de água relativo nas folhas, pigmentos fotossintéticos e biomassa fresca e seca dos brotos em todas as sete populações. Populações de Dingarh Fort, Dingarh Grassland e Haiderwali tiveram maior crescimento do que as de outras populações. As populações de Cholistani, especialmente em Dingarh Grassland e Haiderwali, apresentaram maior capacidade de ajuste osmótico, refletido pelo potencial osmótico e maior acúmulo de proteínas solúveis totais. H2O2 máximo sob estresse hídrico foi observado em populações de Muzaffargarh e Khanewal, mas estas foram intermediárias no conteúdo de MDA. Sob estresse hídrico, as populações de Muzaffargarh e Dingarh Fort tiveram maior acúmulo de K+ em suas folhas. Durante a seca progressiva, as populações não cholistanesas mostraram rolagem completa das folhas após 23 dias de seca, e essas populações não conseguiram suportar mais condições de estresse hídrico, enquanto as populações cholistani toleraram mais condições de estresse hídrico por 31 dias. Além disso, a seca progressiva causou danos ao PSII após 19 dias e tornou-se severa após 23 dias em populações não cholistanesas de P. antidotale do que em populações cholistanesas.

MIA-QSAR study of the structural merging of (thio)benzamide herbicides with photosynthetic system II inhibitory activities.

Benzamide herbicides consist of a class of photosynthetic system II (PSII) inhibitors widely used for weed control. However, the development of resistance by these weeds to the known herbicides requires an ongoing search for new agrochemicals. We report the combination of two congeneric series of (thio)benzamide herbicides into a single data set and subsequent modeling of their herbicidal activities against PSII using MIA-QSAR. The robust and predictive models were used to estimate the pIC50 of new agrochemical candidates, which were proposed based on a chemical mixing of the substructures of the most active compounds present in the data set. The chemical features affecting the herbicidal activities were analyzed using MIA contour maps, whereas the ligand-enzyme interactions responsible for the binding affinities were rationalized through docking studies. The proposed compound possessing a thiobenzamide moiety and C-11 chain, H, NO2, OH, and OH as variable substituents was the most promising alternative.Communicated by Ramaswamy H. Sarma.

Environmentally relevant copper concentrations stimulate photosynthesis in Monoraphidium sp.

Microalgae require copper (Cu) in trace levels for their growth and metabolism, it is a vital component of certain metalloproteins. Although this element has been widely studied concerning microalgae physiology, the effects of environmentally relevant levels have been less studied. We studied the photosynthesis and growth of the Chlorophyte Monoraphidium sp. exposed to Cu ranging from low (1.7 nM) to high (589.0 nM) free Cu ions (Cu2+) concentrations. The growth rate was unaffected by Cu concentrations in the range of 1.7-7.4 nM Cu2+, but decreased beyond it. The relative maximum electron transport rate (rETRm), saturation irradiance (Ek), photochemical quenching (qP and qL), and PSII operating efficiency [Formula: see text] were stimulated in the 3.4-7.4 nM Cu2+ range, concentrations slightly higher than the control, whereas non-photochemical quenching (NPQ) gradually increased with increasing Cu2+. The photosystem II antenna size [Sigma (II)440] increased under high Cu (589.0 nM), which resulted in a decrease in the quinone A (QA) reduction time (tau). In contrast, the QA re-oxidation time was unaffected by Cu exposure. These findings show that a slight increase in Cu stimulated photosynthesis in Monoraphidium sp., whereas high Cu reduced photosynthesis and increased the dissipation of captured light energy. This research is a contribution to the understanding of the dynamic photo-physiological responses of Monoraphidium sp. to Cu ions.

Does silicon and salicylic acid contribute in the morphophysiology of Schinus terebinthifolia seedlings under flooding? / O silício e ácido salicílico contribuem na morfofisiologia de mudas de Schinus terebinthifolia sob alagamento?

Flooding can damage the photosynthetic apparatus and initial growth of Schinus terebinthifolia. We aimed this study evaluates the potential of silicon (Si) and salicylic acid (SA) as mitigating agents on the ecophysiological responses and initial growth of S. terebinthifolia subjected to flooding periods. Seedlings were grown under the following conditions: 1) control (non-flooded): daily irrigation, 2) Flooded (F): storage of seedlings in a 500 L plastic pool, keeping the water depth at ± 2.0 cm above the substrate level, 3) F + 1.0 mM Si, 4) F + 2.0 mM Si, 5) F + 1.5 mM SA, and 6) F + 3.0 mM SA, and evaluated to 15 and 30 days. We observed that flooded seedlings formed hypertrophied lenticels on the stem on the 7th day as a stress adjustment strategy. S. terebinthifolia is sensitive to flooding, although it maintains a stable gas exchange for up to 15 days in this condition. The applications of 1.0 mM Si mitigated the pronounced decrease of gas exchange by 30 days. Using 1.0 mM Si and 3.0 mM SA contributed for integrity of the photosynthetic apparatus and to photochemical activities in the reaction centers, in addition favors to higher seedling biomass and quality under flooding. Foliar application of Si and SA is promising practice for photosynthetic metabolic and initial growth of S. terebinthifolia seedlings under flooded stress.

O alagamento pode promover danos ao aparato fotossintético e crescimento inicial de Schinus terebinthifolia. Objetivamos nesse estudo avaliar o potencial do silício (Si) e ácido salicílico (AS) como agentes de mitigação sobre as respostas ecofisiológicas e crescimento inicial de S. terebinthifolia submetidas a períodos de alagamento. As mudas foram cultivadas sob as seguintes condições: 1) controle (não alagado): irrigação diariamente, 2) Alagado (A): acondicionamento das mudas em piscina plástica de 500 L, mantendo uma lâmina d'água ± 2,0 cm acima do nível do substrato, 3) A + 1,0 mM Si, 4) A + 2,0 mM Si, 5) A + 1,5 mM AS e 6) A + 3,0 mM AS. Observamos que as mudas alagadas formaram lenticelas hipertrofiadas no caule a partir dos 7 dias como estratégia de ajuste ao estresse. S. terebinthifolia é sensível ao alagamento, embora mantenha estável as trocas gasosas por 15 dias nessa condição. A aplicação de 1.0 mM de Si mitigou o decréscimo pronunciado das trocas gasosas por 30 dias. O uso de 1,0 mM Si e 3,0 mM SA contribuíram para a integridade do aparato fotossintético e atividades fotoquímicas nos centros de reação, além de favorecer maior produção de biomassa e qualidade das mudas sob alagamento. A aplicação foliar de Si e AS é uma prática promissora para o metabolismo fotossintético e crescimento inicial de mudas de S. terebinthifolia sob estresse por alagamento.

Adequacy of glyphosate doses in the Merremia cissoides (Lam.) Hallier f. control as a function of light intensity in the growth environments.

Shading interferes with the weed's biology, which can change their sensitivity to post-emergence herbicides. The objective was to evaluate the control of Merremia cissoides with glyphosate in full sunlight and shade conditions in two plant growth stages (30 and 73 days after sowing (DAS)). At 30 and 73 DAS, treatments were established in a 2 × 5 and 2 × 6 factorial scheme, respectively. In both experiments, the growth environments constituted the first factor, and the glyphosate doses the second factor. Shading promoted 50 and 40% reductions in glyphosate doses at 30 and 73 DAS, respectively. At 73 DAS, M. cissoides is 177.77 and 131.48% more tolerant to glyphosate than 30 DAS in shading and full sunlight, respectively. Due to the increase in glyphosate tolerance as the plant grows, the management of M. cissoides should be carried out until the stage of six fully expanded leaves. Increasing glyphosate doses reduced the quantum yield of photosystem II and electron transport rate (ETR) in both growth environments, with ETR data showing a high negative correlation with the control. The doses reductions promoted by shading and glyphosate application in the initial growth stage of M. cissoides reduces costs and the negative environmental impacts of this herbicide use.

Compensatory Transcriptional Response of Fischerella thermalis to Thermal Damage of the Photosynthetic Electron Transfer Chain.

Key organisms in the environment, such as oxygenic photosynthetic primary producers (photosynthetic eukaryotes and cyanobacteria), are responsible for fixing most of the carbon globally. However, they are affected by environmental conditions, such as temperature, which in turn affect their distribution. Globally, the cyanobacterium Fischerella thermalis is one of the main primary producers in terrestrial hot springs with thermal gradients up to 60 °C, but the mechanisms by which F. thermalis maintains its photosynthetic activity at these high temperatures are not known. In this study, we used molecular approaches and bioinformatics, in addition to photophysiological analyses, to determine the genetic activity associated with the energy metabolism of F. thermalis both in situ and in high-temperature (40 °C to 65 °C) cultures. Our results show that photosynthesis of F. thermalis decays with temperature, while increased transcriptional activity of genes encoding photosystem II reaction center proteins, such as PsbA (D1), could help overcome thermal damage at up to 60 °C. We observed that F. thermalis tends to lose copies of the standard G4 D1 isoform while maintaining the recently described D1INT isoform, suggesting a preference for photoresistant isoforms in response to the thermal gradient. The transcriptional activity and metabolic characteristics of F. thermalis, as measured by metatranscriptomics, further suggest that carbon metabolism occurs in parallel with photosynthesis, thereby assisting in energy acquisition under high temperatures at which other photosynthetic organisms cannot survive. This study reveals that, to cope with the harsh conditions of hot springs, F. thermalis has several compensatory adaptations, and provides emerging evidence for mixotrophic metabolism as being potentially relevant to the thermotolerance of this species. Ultimately, this work increases our knowledge about thermal adaptation strategies of cyanobacteria.

Terbuthylazine herbicide: an alternative to atrazine for weed control in glyphosate-tolerant maize.

It is proposed that the herbicide terbuthylazine is more effective than atrazine in controlling weeds in maize. This study aimed to evaluate the efficacy of terbuthylazine and atrazine in a mixture with glyphosate in glyphosate-tolerant maize for post-emergence application. The experiment was conducted over three trials using randomized blocks with 4 repetitions and 10 treatments, composed by terbuthylazine rates + glyphosate, atrazine rates + glyphosate, [atrazine + mesotrione] + glyphosate, atrazine + tembotrione, isolated glyphosate, and nontreated control. Trial 1 were infested with Bidens subalternans DC. and Commelina benghalensis L; trial 2 with Urochloa plantaginea (Link) R. D. Webster, Ipomoea spp., volunteer soybean, B. subalternans, and grasses; and trial 3 infestation with C. benghalensis, U. plantaginea, Ipomoea spp., volunteer soybean, B. subalternans, Amaranthus hybridus L., and grasses. Weed control, crop injury, and yield were evaluated. Terbuthylazine + glyphosate showed an efficacy equivalent to that of atrazine or [atrazine + mesotrione] + glyphosate in the control of broadleaves and C. benghalensis. In contrast, the efficacy of terbuthylazine was similar or greater than that observed for atrazine in controlling grasses, depending on the location. Terbuthylazine is an important partner of glyphosate in controlling weeds in maize and is an alternative to atrazine.

Anacardic Acid Derivatives Affect the in Vitro Reactions of Photosynthesis.

The dichloromethane extract of the cashew nuts from Anacardium occidentale was fractionated by rotation locular countercurrent chromatography aimed at discovering metabolites that could be useful as new models for photosynthesis inhibitors. The chemical fractionation afforded a complex mixture of anacardic acids, which upon catalytic hydrogenation yielded anacardic acid (1). Methylation of 1 via reaction with diazomethane afforded an ester 2. Both compounds were evaluated using polarographic approaches and fluorescence studies of chlorophyll a (ChL a). The in vitro assays informed the decision for the classification of 1 and 2 as Hill reaction inhibitors. Besides that, 1 inhibited the donor side of the PSII, while 2 acted as an energy transfer inhibitor. Therefore, this study is important for the development of herbicides.

Light restriction associated with halosulfuron methyl application efficiently reduces the number and mass of tubers of Cyperus rotundus L.

This study evaluated the effect of light availability in the culture environment and the application of a post emergence herbicide, halosulfuron methyl, on the management of Cyperus rotundus. The experiment was arranged in a 2 × 6 factorial design; the first factor was two levels of light availability: photosynthetically active radiation at 1180.4 and 411.6 µmols m-2 s-1, and the second factor was halosulfuron methyl doses from 28.13 to 140.62 g ha-1. Photosynthetic efficiency, biomass allocation, accumulation of starch in tubers, and percentage control of C. rotundus were evaluated from 7 to 28 days after herbicide application. Doses greater than 70.30 g ha-1 of halosulfuron methyl were efficient to control C. rotundus, regardless of light availability. However, C. rotundus was managed faster under full sunlight than under shading. The efficiency of the photosystem, starch accumulation, and biomass formation decreased with increasing doses of halosulfuron methyl. In a shaded environment, a dose of 28.13 g ha-1 was sufficient to reduce 96.74% of the dry mass and 91.33% of the number of C. rotundus tubers. The decrease in light intensity associated with the use of halosulfuron methyl represents a promising practice for the control of C. rotundus.

The role of silicon in the mitigation of water stress in Eugenia myrcianthes Nied. seedlings / O papel do silício na mitigação do estresse hídrico em mudas de Eugenia myrcianthes Nied

Silicon (Si) is a beneficial element that can mitigate effects of water stress on photosynthetic metabolism and plant growth. Thus, the aimed was to evaluate the effect of Si in mitigating the stressful effect of water deficit and flooding in Eugenia myrcianthes Nied. seedlings. The seedlings received three silicon doses (0, 2, and 4 mmol) and were subjected to two water regimes (I - continuous irrigation and S - water fluctuation, characterized as water stress obtained by two cycles of water regimes: irrigation suspension and flooding). Each cycle was ended when the seedlings had a photosynthetic rate close to zero (P0) when the stressful irrigation condition was normalized until the photosynthetic rate reached the values of the control seedlings (REC). The evaluations were carried out in five periods: T0 - initial seedling condition; 1st and 2nd P0; and 1st and 2nd REC. The E. myrcianthes seedlings reached P0 at 22 and 50 days under water deficit and flooding, respectively. Water stress caused damage to photochemical activities in photosystem II. E. myrcianthes is a species sensitive to water stress, but capable of adjusting to water fluctuation, and the application of 2 mmol Si contributed to the regulation of gas exchange, photochemical yields, and growth of this species at the deficit and flooding phases. We emphasize that E. myrcianthes seedlings have potential for resilience due to physiological plasticity, regardless of the silicon application.

O silício (Si) é um elemento benéfico que pode mitigar os efeitos do estresse hídrico sobre o metabolismo fotossintético e crescimento das plantas. Assim, objetivou-se avaliar o potencial do Si na mitigação do efeito estressante do déficit hídrico e alagamento em mudas de Eugenia myrcianthes Nied. As mudas receberam aplicação de três doses de silício: 0, 2 e 4 mmol e foram submetidas a dois regimes hídricos: (I) - irrigação contínua e (E) flutuação hídrica, caracterizada como estresse hídrico obtido por dois ciclos de regimes hídricos: suspensão da irrigação e alagamento. Cada ciclo foi encerrado quando as mudas apresentaram taxa fotossintética próxima de zero (F0), momento que a condição de irrigação estressante foi normalizada até que a taxa fotossintética alcançasse os valores das mudas controle (REC). As avaliações foram realizadas em cinco períodos: T0 - condição inicial das mudas; 1ª e 2ª F0; 1ª e 2ª REC. As mudas de E. myrcianthes atingiram F0 aos 22 e 50 dias sob déficit hídrico e alagamento, respectivamente. O estresse hídrico promoveu danos nas atividades fotoquímicas no fotossistema II. E. myrcianthes é uma espécie sensível ao estresse hídrico, mas capaz de se ajustar à flutuação hídrica e a aplicação de 2 mmol de Si contribuiu na regulação das trocas gasosas, rendimentos fotoquímicos e crescimento dessa espécie na fase de déficit e alagamento. Ressaltamos que mudas de E. myrcianthes apresentam potencial de resiliência por plasticidade fisiológica independente da aplicação de silício.

Identification of Sorghum (Sorghum bicolor (L.) Moench) Genotypes with Potential for Hydric and Heat Stress Tolerance in Northeastern Mexico.

Sorghum (Sorghum bicolor (L.) Moench) is cultivated in regions with frequent drought periods and high temperatures, conditions that have intensified in the last decades. One of the most important photosynthetic components, sensible to hydric stress, is maximum quantum yield for photosystem II (PSII, or Fv/Fm). The objective of the present study was to identify sorghum genotypes with tolerance to hydric and heat stress. The treatments were hydric status (hydric stress or non-hydric stress (irrigation)), the plant's developmental stages (pre or post-anthesis), and six genotypes. The response variables were Fv/Fm; photosynthetic rate (PN); stomatal conductance (gs); transpiration rate (E); relative water content (RWC); damage to cell membrane (DCM) at temperatures of 40 and 45 °C; and agronomic variables. The experiment was conducted in pots in open sky in Marín, N.L., in the dry and hot northeast Mexico. The treatment design was a split-split plot design, with three factors. Hydric stress diminished the functioning of the photosynthetic apparatus by 63%, due to damage caused to PSII. Pre-anthesis was the most vulnerable stage to hydric stress as it decreased the weight of grains per panicle (85%), number of grains per panicle (69%), and weight of 100 grains (46%). Genotypes LER 1 and LER 2 were identified as tolerant to hydric stress, as they had lower damage to PSII; LER 1 and LEB 2 for their superior RWC; and LER 1 as a thermo tolerant genotype, due to its lower DCM at 45 °C. It was concluded that LER 1 could have the potential for both hydric and heat stress tolerance in the arid northeast Mexico.

Evaluation of Chalcone Derivatives as Photosynthesis and Plant Growth Inhibitors.

We report the evaluation of chalcone derivatives as photosystem II (PSII) and plant growth inhibitors. Chalcone derivatives were evaluated as PSII inhibitors through Chl a fluorescence measurement. (E)-Chalcone (6a) and (E)-3-(4-bromophenyl)-1-(4-fluorophenyl)prop-2-en-1-one (6j) showed the best results, reducing the performance index on absorption basis parameter (PIabs ) by 70 %. Additionally, the decrease of TR0 /RC and ET0 /RC parameters indicates that the chalcone derivatives limited the number of active PSII reaction centers and the amount of trapped energy within them. Compounds 6a and 6j both act as post-emergent herbicides at 50 µM, reducing the root biomass of the Ipomoea grandifolia weed by 72 % and 83 %, respectively, corroborating the fluorescence results. The selectivity against weeds as compared to valuable crops by compounds 6a and 6j were evaluated employing Zea mays and Phaseolus vulgaris plants. In these, our newly synthesized compounds showed no effects on biomass accumulation of roots and aerial parts when compared to the control, providing valuable evidence for the role of these compounds as selective inhibitors of the growth of undesired weeds.

Weed control and soybean agronomic performance in response to application of sulfentrazone + diuron in pre-emergence / Controle de plantas daninhas e desempenho agronômico de soja em resposta à aplicação de sulfentrazone + diuron em pré-emergência

The use of pre-emergent herbicides is an important tool in weedmanagement. Sulfentrazone + diuron mixture was recently launched ontothe market. The objectiveof this work was to evaluate the weed control and the agronomic performance of soybean in response to application of sulfentrazone + diurondoses in pre-emergence. The experiment was conducted in Londrina PR, in an oxisol. The treatments were doses ofsulfentrazone + diuron (62 + 123, 123 + 245, 184 + 368, 245 + 490, 306 + 613 e 368 + 735 g a.i.ha-1). In addition to these treatments, isolated applications of sulfentrazone (245 g a.i.ha-1) and diuron (490 g a.i.ha-1) were evaluated, as well as a weedyand aweed-freecontrol. For the weed control, the wild radish(Raphanus raphanistrum)and itchgrass (Rottboellia cochinchinensis) emergencewere evaluated. In soybean, photosystem II (PSII)activity, stand, plant height, number of podsper plant, height of insertion of the first pod, number of nodes per plant, mass of a thousand grains and grain yield were evaluated. Results show that the mixture of sulfentrazone + diuron resulted in less than 50% wild radish control, regardless of the dose evaluated. However, for itchgrass, the control was greater than 90% in doses from 123 g sulfentrazone + 245g diurona.i.ha-1. Regarding thesoybeancrop, in doses from 245 g sulfentrazone + 490 g diuron a.i. ha-1 there was a greater number of pods per plant and higher grain yield, of about3,000 kg ha-1. The application of herbicides led to a transient inhibition of PSIIactivity, which did not result in a reduction in crop grainyield, indicating plant recovery. Therefore, the mixture of sulfentrazone + diuron is a good alternative for the weed management in pre-emergence of soybean, and should be positioned according to the history of fieldinfestation.

A utilização de herbicidas pré-emergentes é uma ferramenta importante no manejo de plantas daninhas. Recentemente foi lançada no mercado a mistura de sulfentrazone + diuron. O objetivo deste trabalho foi avaliar o controle de plantas daninhas e o desempenho agronômico da soja em resposta à aplicação de doses de sulfentrazone + diuron em pré-emergência. O experimento foi conduzido em Londrina PR, em latossolo. Os tratamentos avaliados foram doses de sulfentrazone + diuron (62 + 123, 123 + 245, 184 + 368, 245 + 490, 306 + 613 e 368 + 735 g i.a.ha-1).Além desses tratamentos, foram avaliadas as aplicações isoladas de sulfentrazone (245 g i.a.ha-1) e de diuron (490 g i.a.ha-1), além de uma testemunha infestada e outra capinada. Foram avaliados os controles de nabiça (Raphanus raphanistrum) e de capim-camalote(Rottboellia cochinchinensis). Na soja, foram avaliados a atividade do fotossistema II (FSII), a emergência, estatura de plantas, número de legumes por planta, altura de inserção do primeiro legume, número de nós por planta, massa de mil grãos e produtividade de grãos. A mistura desulfentrazone + diuron apresentoucontrole de nabiçainferior a 50%, independentemente da dose avaliada. No entanto, para o capim-camalote, o controle foi satisfatório, sendo superior a 90% em doses a partir de 123g sulfentrazone+ 245 g diuroni.a.ha-1. Em relação àsoja, em doses a partir de 245g sulfentrazone+ 490 gdiuroni.a.ha-1houve maior número de legumes por planta e maior produtividade de grãos, de aproximadamente 3.000 kg ha-1. A aplicação dos herbicidas levou a uma inibição transitória da atividade doFSII, a qual não resultou em redução da produtividade da cultura, indicando a recuperação das plantas. Portanto, a mistura de sulfentrazone + diuron é uma boa alternativa para o manejo de plantas daninhas em pré-emergência da cultura da soja, devendo ser posicionadade acordo com o histórico de infestação da lavoura.

Weed control and soybean agronomic performance in response to application of sulfentrazone + diuron in pre-emergence / Controle de plantas daninhas e desempenho agronômico de soja em resposta à aplicação de sulfentrazone + diuron em pré-emergência

The use of pre-emergent herbicides is an important tool in weedmanagement. Sulfentrazone + diuron mixture was recently launched ontothe market. The objectiveof this work was to evaluate the weed control and the agronomic performance of soybean in response to application of sulfentrazone + diurondoses in pre-emergence. The experiment was conducted in Londrina PR, in an oxisol. The treatments were doses ofsulfentrazone + diuron (62 + 123, 123 + 245, 184 + 368, 245 + 490, 306 + 613 e 368 + 735 g a.i.ha-1). In addition to these treatments, isolated applications of sulfentrazone (245 g a.i.ha-1) and diuron (490 g a.i.ha-1) were evaluated, as well as a weedyand aweed-freecontrol. For the weed control, the wild radish(Raphanus raphanistrum)and itchgrass (Rottboellia cochinchinensis) emergencewere evaluated. In soybean, photosystem II (PSII)activity, stand, plant height, number of podsper plant, height of insertion of the first pod, number of nodes per plant, mass of a thousand grains and grain yield were evaluated. Results show that the mixture of sulfentrazone + diuron resulted in less than 50% wild radish control, regardless of the dose evaluated. However, for itchgrass, the control was greater than 90% in doses from 123 g sulfentrazone + 245g diurona.i.ha-1. Regarding thesoybeancrop, in doses from 245 g sulfentrazone + 490 g diuron a.i. ha-1 there was a greater number of pods per plant and higher grain yield, of about3,000 kg ha-1. The application of herbicides led to a transient inhibition of PSIIactivity, which did not result in a reduction in crop grainyield, indicating plant recovery. Therefore, the mixture of sulfentrazone + diuron is a good alternative for the weed management in pre-emergence of soybean, and should be positioned according to the history of fieldinfestation.(AU)

A utilização de herbicidas pré-emergentes é uma ferramenta importante no manejo de plantas daninhas. Recentemente foi lançada no mercado a mistura de sulfentrazone + diuron. O objetivo deste trabalho foi avaliar o controle de plantas daninhas e o desempenho agronômico da soja em resposta à aplicação de doses de sulfentrazone + diuron em pré-emergência. O experimento foi conduzido em Londrina PR, em latossolo. Os tratamentos avaliados foram doses de sulfentrazone + diuron (62 + 123, 123 + 245, 184 + 368, 245 + 490, 306 + 613 e 368 + 735 g i.a.ha-1).Além desses tratamentos, foram avaliadas as aplicações isoladas de sulfentrazone (245 g i.a.ha-1) e de diuron (490 g i.a.ha-1), além de uma testemunha infestada e outra capinada. Foram avaliados os controles de nabiça (Raphanus raphanistrum) e de capim-camalote(Rottboellia cochinchinensis). Na soja, foram avaliados a atividade do fotossistema II (FSII), a emergência, estatura de plantas, número de legumes por planta, altura de inserção do primeiro legume, número de nós por planta, massa de mil grãos e produtividade de grãos. A mistura desulfentrazone + diuron apresentoucontrole de nabiçainferior a 50%, independentemente da dose avaliada. No entanto, para o capim-camalote, o controle foi satisfatório, sendo superior a 90% em doses a partir de 123g sulfentrazone+ 245 g diuroni.a.ha-1. Em relação àsoja, em doses a partir de 245g sulfentrazone+ 490 gdiuroni.a.ha-1houve maior número de legumes por planta e maior produtividade de grãos, de aproximadamente 3.000 kg ha-1. A aplicação dos herbicidas levou a uma inibição transitória da atividade doFSII, a qual não resultou em redução da produtividade da cultura, indicando a recuperação das plantas. Portanto, a mistura de sulfentrazone + diuron é uma boa alternativa para o manejo de plantas daninhas em pré-emergência da cultura da soja, devendo ser posicionadade acordo com o histórico de infestação da lavoura.(AU)

Effects of Acetogenins from Annona coriacea on the in Vitro Reactions of Photosynthesis.

Our search for candidates for photosynthesis inhibitors is allowing us to report the effect of two acetogenins identified in Annona coriacea Mart. leaves, ACG-A and ACG-B, a non-adjacent bis-THF and a mono-THF types, respectively. This is an important class of natural products which presents biological properties such as anticancer, neurotoxic, larvicidal and insecticidal. However, this is only the second report associated to its herbicidal activity. Their mechanisms of action on the light reactions of the photosynthesis were elucidated by polarographic techniques. Compounds inhibited the noncyclic electron transport on basal, phosphorylating, and uncoupled conditions from H2 O to methyl viologen (MV); therefore, they act as Hill reaction inhibitors. Studies on fluorescence of chlorophyll a (ChL a) indicated that they inhibited the acceptor side of PSII between P680 and PQ-pool, exactly as the commercial herbicide DCMU does.

Chlorophyll a fluorescence and leaf temperature are early indicators of oil palm diseases

Bud rot (BR) caused by Phytophthora palmivora and lethal wilt (LW) whose causal agent is unknown, are two diseases currently posing a threat to the oil palm ( Elaeis guineensis . Jacq) industry. BR, first reported in 1964, has destroyed more than 85,000 ha. LW, first reported in 1994 in the Llanos Orientales in Colombia, has destroyed more than 5,000 ha. Chlorophyll a fluorescence is useful as a provider of information about the efficiency of the photosynthetic process when plants are subjected to biotic or abiotic stresses. Oil palms affected by BR and LW showed anomalies in the photosynthetic system, manifested by reductions in Fv / F M and PSII. Changes in PSII, variable fluorescence yield ( Fv ) and maximum fluorescence in light-adapted leaves ( F M ) were observed from the start of BR infection. The most sensitive and early indicators of LW disease were leaf temperature and basal fluorescence ( F 0 ). Fv/F 0 significantly changed in diseased palms, indicating problems with movement of electrons through the electron transport chain. Leaf temperature changed in response to both diseases, but variation was greater in LW. We concluded that damage to the photochemical system caused by the diseases affected the processes by which the plant captures and transports energy, causing a physiological imbalance in the plant reflected in the observed variations in chlorophyll a fluorescence and leaf temperature. The two parameters began to change early in the onset of BR and before visual symptoms appeared in LW, which is very important to the management of both diseases, the foundation of which is early detection.(AU)

Chlorophyll a fluorescence and leaf temperature are early indicators of oil palm diseases

Bud rot (BR) caused by Phytophthora palmivora and lethal wilt (LW) whose causal agent is unknown, are two diseases currently posing a threat to the oil palm ( Elaeis guineensis . Jacq) industry. BR, first reported in 1964, has destroyed more than 85,000 ha. LW, first reported in 1994 in the Llanos Orientales in Colombia, has destroyed more than 5,000 ha. Chlorophyll a fluorescence is useful as a provider of information about the efficiency of the photosynthetic process when plants are subjected to biotic or abiotic stresses. Oil palms affected by BR and LW showed anomalies in the photosynthetic system, manifested by reductions in Fv / F M and PSII. Changes in PSII, variable fluorescence yield ( Fv ) and maximum fluorescence in light-adapted leaves ( F M ) were observed from the start of BR infection. The most sensitive and early indicators of LW disease were leaf temperature and basal fluorescence ( F 0 ). Fv/F 0 significantly changed in diseased palms, indicating problems with movement of electrons through the electron transport chain. Leaf temperature changed in response to both diseases, but variation was greater in LW. We concluded that damage to the photochemical system caused by the diseases affected the processes by which the plant captures and transports energy, causing a physiological imbalance in the plant reflected in the observed variations in chlorophyll a fluorescence and leaf temperature. The two parameters began to change early in the onset of BR and before visual symptoms appeared in LW, which is very important to the management of both diseases, the foundation of which is early detection.

Effect of cadmium on young plants of Virola surinamensis.

The steady increase in cadmium (Cd) levels in the environment from anthropogenic actions has contributed to environmental degradation. Virola surinamensis is a forest species that has desirable characteristics such as deep and dense roots, relatively rapid growth and high biomass production to remedy contaminated environments by Cd. The aim of this study was to assess the physiological responses and the phytoextraction and tolerance capacity of young plants of V. surinamensis submitted to Cd concentrations. The experimental design was a completely randomized design with five Cd concentrations (0, 15, 30, 45 and 60 mg L-1) for 60 days. Leaf water potential (Ψpd), stomatal conductance (gs) and transpiration (E) reduced in plants exposed to Cd. Lower values of maximum photochemical efficiency of photosystem II (Fv/Fm), electron transport rate (ETR) and photochemical quenching coefficient (qP) were accompanied by reduction of photosynthesis (A) with increasing concentrations of Cd, although the non-photochemical quenching coefficient (NPQ), and intercellular CO2 concentration (Ci) showed increase. Instantaneous water-use efficiency (A/E), net photosynthesis to intercellular CO2 concentration ratio (A/Ci) and total chlorophyll (Chl) reduced with increasing levels of Cd. Cadmium concentrations increased in different plant tissues (root > stem > leaf). The tolerance index (TI) indicated that V. surinamensis presented medium and high tolerance to Cd. The results of bioconcentration factor (BCF) and translocation factor (TF) showed low plant efficacy in Cd phytoextraction and suggest that V. surinamensis may be promising for phytostabilization of Cd.