Comportamento estomático e componentes do sistema antioxidante em cafeeiros sob estresse hídrico

Para o cafeeiro (Coffea arabica) existe uma comprovada relação positiva entre fechamento estomático e formação e acúmulo de H2O2. Entretanto, tal relação para a cultura sob restrição hídrica ainda não foi estudada. Avaliou-se o movimento estomático e a capacidade antioxidante em mudas de cafeeiro sob diferentes regimes hídricos. Mudas de cafeeiro cv. Catuaí IAC 99, com oito meses de idade, foram submetidas à capacidade de campo, suspensão gradativa e suspensão total da irrigação por um período de 21 dias. Foram realizadas avaliações do potencial hídrico (Ψw) foliar na antemanhã e resistência estomática, taxa transpiratória e déficit de pressão de vapor foram avaliados as 10h00 e 17h00. As determinações bioquímicas e enzimáticas foram realizadas em folhas coletadas às 17h00. Todas as avaliações e coletas foram realizadas em intervalos de três dias. Nas plantas em capacidade de campo não houve variação no Ψw durante o período de avaliação. Para a suspensão gradativa da irrigação, houve queda expressiva a partir dos 12 dias, chegando próximo a -2,5 Mpa, ao final do experimento. Já nas plantas em suspensão total da irrigação observou-se queda no Ψw a partir do sexto dia, chegando a -2,5 MPa aos 15 dias. A queda no Ψw para as plantas em suspensão gradual e total da irrigação refletiu em aumentos na resistência estomática e diminuição da taxa transpiratória, ocasionando aumento na formação de peróxido de hidrogênio e nos períodos finais, aumentos na peroxidação de lipídios. Em conseqüência obervaram-se aumentos na atividade das enzimas antioxidantes, bem como nos teores de ascorbato e dehidroascorbato, atuando na detoxificação dos radicais livres formados em função do estresse.Coffee (Coffea arabica) plants show a positive relationship between stomatal closure and formation and accumulation of H2O2. However, for coffee plants under water restriction such relationship has never been studied. The objective of the present study was evaluate the stomatal movement and the antioxidant capacity of coffee seedlings under different water regimes. Eight months old coffee seedlings of cv. Catuaí IAC 99 were submitted to field capacity, gradual and total suspension of irrigation during a period of 21 days. Evaluations of leaf water potential (Ψw) were performed in the beginning of the morning, and stomatal resistance, transpiration rate and vapor pressure deficit were determined at 10 am and 5 pm. All biochemical and enzymatic determinations were performed in leaves collected at 5 pm. Evaluations and samplings were performed at three days intervals. There was no variation in Ψw during the evaluated period for plants in field capacity. However, an expressive decrease of Ψw following day 12, reaching values near -2.5 MPa at the end of the experiment was observed for plants submitted to gradual suspension of irrigation. For plants submitted to total suspension of irrigation, Ψw decreases after the sixth day, reaching -2.5 MPa at day 15. The decay of Ψw in plants submitted to gradual and total suspension of irrigation reflected in increased stomatal resistance and in a decreased transpiration rate leading to an increase in hydrogen peroxide formation and, on final stages, increase in lipid peroxidation. As a conclusion, an increase in the activity of antioxidant enzymes as well as in the levels of ascorbate and dehydroascorbate was observed, which act in the detoxification of free radicals formed as result of the water stress

Flexibility of C 4 decarboxylation and photosynthetic plasticity in sugarcane plants under shading

The flexibility between C4 photosynthetic sub-types NADP-malic enzyme (NADP-ME) and phosphoenolpyruvate carboxykinase (PEPCK), recently identified in some C4 species, confers high photosynthetic efficiency under varying light conditions. Theoretically, PEPCK decarboxylation uses less quanta per CO2 fixed than NADP-ME, suggesting an increase in PEPCK activity could be advantageous under shading, as CO2 leakiness increases under low light. Thus, we hypothesize that sugarcane plants have flexibility among the decarboxylation pathways, i.e., more than one decarboxylation route occurs independent of the environmental condition; furthermore, low light availability induces biochemical and anatomical adjustments resulting in increased PEPCK activity, which could contribute to maintaining or even increasing quantum efficiency of CO2 assimilation under limiting light. Two sugarcane varieties were evaluated and both presented activities of the three decarboxylases, either under full sunlight or shading. In vitro PEPCK activity increased in plants grown under low light, suggesting an upregulation of this decarboxylation pathway. Accordingly, changes in chloroplast arrangement of bundle sheath cells from centrifugal to evenly distributed were found. Our data suggest that such biochemical and anatomical adjustments found in sugarcane grown under shading were important to maintain the maximum quantum efficiency of CO2 assimilation. Finally, we propose a model highlighting the integration between the decarboxylation pathways under shading, considering carboxylation and decarboxylation pathways in sugarcane plants

Rescuing the Brazilian Agave breeding program: morphophysiological and molecular characterization of a new germplasm

Agaves have been a valuable resource in dryland areas for centuries, providing fibers (sisal), food, and beverages. However, the advent of synthetic fibers has led to a decrease in research on Agave, resulting in the cessation of breeding programs in Brazil. With the rise of climate change, there is renewed interest in Agave for its potential as a biofuel feedstock in semiarid regions. Since 2016, we have been collecting Agave accessions throughout the country and retrieving what is left of Brazil’s original breeding program to establish a new germplasm bank. Here, we evaluated 21 of those accessions growing in the field. We used molecular markers and morphophysiological traits to characterize the plants. Based on the Mayahuelin molecular marker, we were able to reconstruct a phylogeny for the Brazilian accessions. The morphophysiological traits explained 34.6% of the phenotypic variation in the dataset, with physiological traits such as leaf water content, effective quantum efficiency of photosystem II (ΦPSII), and specific leaf mass (SLM) as the most significant traits. Specifically, we evaluated nine Agave species and found that the physiological traits, rather than the morphological ones, were the most significant. Leaf water content was negatively correlated with specific leaf mass, which could be used as a marker for selecting cultivars with higher biomass accumulation. Interestingly, ΦPSII and chlorophyll content were negatively correlated, suggesting photochemical adaptations throughout the rosette. Molecular and phenotypic data suggest that A. amaniensis, which is frequently considered a synonym of A. sisalana, is effectively another species. Overall, this study provides valuable information on the physiological traits of Brazilian Agave accessions and is a starting point for selecting more productive and climate-resilient cultivars for biorenewables production

Toxicity of arsenic and nitric oxide in the mediation of cellular responses in lettuce (Lactuca sativa L.)

Plantas de alface ((Lactuca sativa L. cv Hanson) Asteraceae) foram submetidas a níveis tóxicos de arsênio (As) com o objetivo de induzir o estresse oxidativo e avaliar o papel do óxido nítrico (NO), fornecido via SNP, como agente atenuante desse estresse. As plantas foram tratadas com 50 μM de As, com ou sem SNP, na concentração de 100 μM, adicionados à solução nutritiva durante o período de 4, 12 e 24 horas. A concentração de H2O2, O2 .- e MDA foram determinadas, além da atividade das enzimas catalase (CAT), dismutase do superóxido (SOD), peroxidase (POX), peroxidase do ascorbato (APX), redutase da glutationa (GR) e peroxidase da glutationa (GPX), a concentração de As e detecção de NO através da microscopia confocal. Plantas de alface expostas ao As apresentaram elevada concentração desse elemento nas folhas, em média 6,3 μg g-1 de MS, durante o período de 24 horas, mostrando rápida absorção e translocação para a parte aérea. Elevadas concentrações de As nas folhas foram acompanhadas de significativo incremento nas concentrações de H2O2 e MDA. A presença de SNP, no entanto, atuando como doador de NO, promoveu redução na concentração do H2O2. As atividades das enzimas nas plantas expostas ao As aumentou significativamente, indicativo da participação na redução do estresse induzido pelo metaloide. Nas plantas expostas ao As e SNP, as atividades enzimáticas foram reduzidas, possivelmente pela ação direta do NO sobre os metabólitos tóxicos produzidos durante o estresse. Nas plantas submetidas ao estresse por As, observou-se maior produção de NO, resultado comprovado pelo aumento na fluorescência. Quando fornecido na forma exógena, o NO também agiu diretamente na remoção de metabólitos tóxicos gerados em resposta ao As. Assim, verificou-se que o NO, fornecido pelo SNP, ameniza a toxicidade do As sobre folhas de alface.Lettuce plants ((Lactuca sativa L. cv Hanson) Asteraceae) were exposed to different arsenic (As) toxic levels aiming to induce the oxidative stress and evaluate the role of nitric oxide (NO), given as SNP, as an attenuating agent of this kind of stress. Plants were treated with 50 μM As, with or without SNP at the concentration of 100 μM, added to the nutrient solution in 4, 12 and 24 hours. The concentration of H2O2, O2 - and MDA, the enzymatic activities pf catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione peroxidase (GPX) and the As and NO concentration were measured. Lettuce plants exposed to As showed elevated As concentration in leaves, in average 6,3 μg g-1 DW, in the short period of 24 hours with fast uptake and translocation to the leaves. The high As concentration detected in leaves were followed by a significant increase in H2O2 and MDA concentrations. SNP presence, however, acting as NO donator promoted reduction in the concentration of these oxidative agents. The enzymatic activities in the plants exposed to As were increased which indicates an active participation of these enzymes as part of the strategy to reduce the oxidative stress induced by the metalloid. In the plants exposed to As and SNP, theses activities were reduced, possibly related to the NO direct action in the scavenging of the generated toxic metabolites. In the plants exposed to As, there was higher production of NO observed through the high fluorescence intensity. When given as an exogenous form, No acted directly in the scavenging of the toxic metabolites generated in response to As exposure. Therefore, it was observed that NO, given as SNP, attenuate As-induced toxicity in lettuce leaves.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Phytotoxic effects of plastic pollution in crops : what is the size of the problem?

Plastic pollution is one of the most impactful human interferences in our planet. Fragmentation of plastic leads to nano- and microplastics (NP/MP) formation, which accumulate in agricultural lands, representing an increasing risk for crop production and food safety. It has been shown that MP promote damage in plant tissues by several direct and indirect ways, and that NP can enter the tissues/cells and accumulate in edible organs. Investigation of the phytotoxic effects of NP/MP in plants started only in 2016, with most of the studies performed with crops. Since contradictory results are often observed, it is important to review the literature in order to identify robust effects and their possible mechanisms. In this review, we discuss the potential of NP/MP in damaging crop species, with focus on the physiological changes described in the literature. We also performed scientometrics analyses on research papers in this field during 2016–2021, to reveal the research situation of phytotoxic effects of plastic pollution in crops. Our review is as a starting point to help identify gaps and future directions in this important, emerging field

Technology seed Sebastiania membranifolia Mull Arg (Euphorbiaceae)

Sebastiania membranifolia, popularly known as sarandi, is a tree species native to Brazil, usually found in land of alluvial floodplains and river banks, suitable for restoration of degraded areas. Despite the commercial importance of this species, little is known about its mechanisms of propagation. This research evaluated the germinating seeds under different conditions of temperature, substrate and light, and determined methods of scarification in order to establish a suitable protocol for sexual propagation. The study was conducted in chambers with BOD and thermal control photoperiod, testing the following treatments: temperatures of 25, 30 and alternating 20/30º C; substrates (sand-EA, on paper-SP and from paper -EP), four solutions gibberellin (50, 100, 200, 400 mgL-1); potassium nitrate (0.1, 0.2, 0.3 and 0.4%) in the presence (12 h photoperiod) and absence of light. The experimental design was completely randomized with four replications of 50 seeds each. We found that the average degree of seed moisture was 10.4% and the weight of a thousand seeds (PMS) of 3.16 g. The highest percentage of germination was obtained with photoperiod at 25 º C, on paper (SP) and between role (EP). The concentrations of 100 mg L-1 gibberellin and 0.1% potassium nitrate showed higher germination and vigor. Seed treatment with a gibberellin solution of 100 mgL-1 favored the growth of seedlings, unlike potassium nitrate that inhibit the growth even at low concentration

GROWTH AND CARBOHYDRATE PARTITION OF Sebastiania membranifolia PLANS SUBMITTED TO FLOODING

The aim of this study was to evaluate the growth and carbohydrate\ud partitioning in seedlings of Sebastiania membranifolia in response to flooding. Seeds\ud were germinated in BOD type chamber at 25 ºC, on moistened germitest paper. The\ud seedlings were acclimatized for 20 days in a growth chamber and then transplanted into\ud polypropylene bags containing substrate consisting of sand , manure and soil (1:1:1), and\ud transferred to a greenhouse protected with 50% shading for 40 days. At the end of this\ud period three treatments were established: control (well watered), root flooded and\ud completely flooded. The flooding was accomplished by placing the bags containing the\ud plants individually in buckets with greater capacity. The evaluations were conducted at\ud intervals of 12 days for a total period of 36 days, with four replicates for each treatment\ud and evaluation period. The number of leaves, branches, stem height and dry weight of\ud these parts, increased linearly in control plants over the period analyzed. For the flooded\ud roots treatment, these parameters increased only until the 24th day, and in completely\ud flooded plants, in general, this stress did not allow the growth of plants. The content of\ud total soluble sugars, reducing sugars and starch were significantly lower in completely\ud flooded plants, both in the leaves and in the roots. Root flooded plants had significant starch\ud reduction in the roots, with values of the last measurement equal to those observed in\ud completely flooded plants. These results suggest that S. membranifolia may be a promising\ud species for revegetation of depleted areas subject to intermittent flooding

Photosynthesis and biomass accumulation in young sugarcane plants grown under increasing ammonium supply in nutrient solution

The aim of this study was to evaluate the sugarcane responses to varying ammonium:nitrate (NH4+:NO3-) ratio and to reveal how much NH4+ plants can tolerate before showing impairment of photosynthesis and growth. Sugarcane plants were grown in nutrient solution with the following NH4+:NO3- ratios (%): 20:80; 30:70; 40:60; 60:40; 70:30; and 80:20. The lowest photosynthetic rates, stomatal conductance, instantaneous carboxylation efficiency and leaf chlorophyll a content were found in plants supplied with higher than 60% NH4+. The leaf content of chlorophyll b proved to be more sensitive than chlorophyll a and decreases were found from 40% NH4+. We did not observe significant differences in leaf NO3- concentration under varying NH4+:NO3- ratio. However, plants that received 80% NH4+ showed the highest leaf NH4+ concentration and lowest leaf [NO3-]:[NH4+] ratio. The estimated leaf nitrogen content was higher in plants supplied with 20% and 30% NH4+. Taken together, our data revealed that sugarcane plants are sensitive to NH4+, with photosynthesis and plant growth being impaired when NH4+ supply was higher than 30% in nutrient solution. Root biomass was significantly reduced under high NH4+ supply, which explains decreases in stomatal conductance. Besides stomatal limitation, photosynthesis was also limited by low carboxylation efficiency under high NH4+ supply. Apparently, leaf NH4+ concentrations higher than 1.0 mu mol g(-1) were enough to impair photosynthesis. The balance between [NO3-] and [NH4+] in leaves was more correlated to photosynthesis than either [NO3-] or [NH4+] alone313401411CAPES - Coordenação de Aperfeiçoamento de Pessoal e Nível SuperiorCNPQ - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPESP – Fundação de Amparo à Pesquisa Do Estado De São Paulonão temnão tem2017/11279-7MDP acknowledges the scholarship provided by the São Paulo Research Foundation (FAPESP, Brazil; Grant No. 2017/11279-7). NMS acknowledges the fellowship granted by the National Program of Post-Doctorate (PNPD), Coordination for the Improvement of Higher Education Personnel (Capes, Brazil). ECM, LS and RVR acknowledge the fellowships granted by the National Council for Scientific and Technological Development (CNPq, Brazil