Danos causados por estresse salino sobre a fotossíntese de plantas jovens de pinhão-manso

Salinity is a major limiting factor to crop productivity in the world especially in semiarid regions. The aim of this study was to evaluate the photosynthetic resistance of Jatropha curcas (L.) young plants subjected to salt stress. The experiment was carried out in a completely randomized design with treatments in a 2 x 3 factorial: two NaCl levels (0 and 100 mmol L-1) and three harvest times: 7 and 14 days of salt exposure and three days of recovery. Leaf Na+ and Cl-concentrations and the K+/Na+ ratios, after seven days of salt exposure, did not reach ionic toxic levels, suggesting that the NaCl-induced osmotic effects prevailed over the ionic ones. Under this condition, the salt stress caused reduction in leaf gas exchange parameters, such as CO2 fixation, stomatal conductance and transpiration. In contrast, salt stress did not change the photochemical efficiency of photossystem II. Conversely, after 14 days of treatment, Na+ and Clions reached very high concentrations, up to toxic levels in leaves. Under such conditions, both leaf gas exchange and photochemistry suffered strong impairment probably caused by ionic toxicity. The recovery treatment for 3d did not significantly decrease the leaf salt concentrations and no improvement was observed in the photosynthetic performance. Physic nut young plants are sensitive to high NaCl-salinity conditions, with high leaf Na+ and Cl- concentrations, low K+/Na+ ratio and great photosynthetic damages due to stomatal and biochemical limitations.A salinidade é um dos principais fatores que limitam a produtividade das culturas no mundo principalmente em regiões semiáridas. Avaliou-se a resistência da fotossíntese de plantas jovens de pinhãomanso (Jatropha curcas L.) submetidas ao estresse salino. O experimento foi realizado em delineamento inteiramente casualizado com tratamentos em fatorial 2 x 3: duas concentrações de NaCl (0 e 100 mmol L-1) e três tempos de avaliação (7 e 14 dias de exposição e três dias de recuperação). As concentrações de Na+ e Cl- e a relação K+/Na+ nas folhas, após sete dias de exposição ao sal, não indicaram níveis tóxicos, sugerindo os efeitos osmóticos induzidos pelo NaCl prevaleceram sobre as causas iônicas. Sob essas condições, o estresse salino causou redução nos parâmetros de trocas gasosas, como fixação de CO2, condutância estomática e transpiração, mas ao contrário, não alterou a eficiência fotoquímica do fotossistema II. Após 14 dias de tratamento, os íons salinos atingiram concentrações muito elevadas nas folhas, provavelmente atingindo níveis tóxicos. Em tais condições, as trocas gasosas e a atividade fotoquímica sofreram forte redução causada pelo estresse iônico. O tratamento de recuperação não induziu queda intensa nas concentrações dos íons salinos nas folhas e nenhuma melhoria foi observada no desempenho fotossintético. Plantas jovens de pinhão manso são sensíveis a condições de salinidade elevada por NaCl, mostrando altas concentrações de Na+ e Cl-, baixa razão K+/Na+ e danos fotossintéticos intensos causados tanto por limitações estomáticas como por limitações bioquímicas

Contribuição de solutos orgânicos e inorgânicos no ajustamento osmótico de pinhão-manso submetido à salinidade

The objectives of this work were to evaluate the organic and inorganic solutes accumulation and measure their contribution to the osmotic adjustment of physic nut (Jatropha curcas L.) leaves under salinity. The experiment was carried out using a completely randomized design with five treatments (0, 25, 50, 75, and 100 mmol L-1 of NaCl) and four replications. Plants were hydroponically grown under greenhouse controlled conditions of photoperiod (12 hours), temperature (average of 28ºC), relative humidity (average of 65%), and with maximum photosynthetically active radiation average of 700 µmol m-1 s-1. The leaf osmotic potential decreased progressively, changing from -0.84 to -2.05 MPa, while the relative water content increased in the 75 and 100 mmol L-1 treatments. The relative contribution of Na+ and Cl- ions were the most important quantitatively for the leaf osmotic adjustment of salt-treated plants, 52 and 20%, respectively. The relative contribution of K+ decreased significantly with added salt, changing from 17 to 5% as the NaCl level increased from 25 to 100 mmol L-1. The average contribution of sugars, amino acids, glycinebetaine, and proline was approximately 5.5, 6, 4, and 0.03%, respectively. The physic nut leaves exhibited an effective osmotic adjustment under salinity, maintaining their hydration status, mainly via Na+ and Cl- accumulation. Glycinebetaine was more important to osmotic adjustment than proline in both salt-treated and untreated plants.O objetivo deste trabalho foi avaliar a acumulação de solutos orgânicos e inorgânicos e suas contribuições para o ajustamento osmótico de folhas de pinhão-manso (Jatropha curcas L.) submetido à salinidade. O experimento foi conduzido em delineamento experimental inteiramente casualizado, com cinco tratamentos (0, 25, 50, 75 e 100 mmol L-1 de NaCl) e quatro repetições. As plantas foram cultivadas hidroponicamente em casa de vegetação, em condições controladas de fotoperíodo (12 horas), temperatura (média de 28ºC) e umidade relativa do ar (média de 65%), com radiação fotossinteticamente ativa máxima média de 700 µmol m-1 s-1. O potencial osmótico das folhas decresceu progressivamente e variou de -0,84 a -2,05 MPa, enquanto o conteúdo relativo de água aumentou nos tratamentos com 75 e 100 mmol L-1. Os íons Na+ e Cl- foram os mais importantes, em termos quantitativos, e contribuíram com cerca de 52 e 20%, respectivamente, para o ajustamento osmótico das folhas de plantas tratadas com NaCl. A contribuição do K+ decresceu de modo acentuado e foi de 17 e 5% nos tratamentos com 25 e 100 mmol L-1 de NaCl. A contribuição média dos solutos orgânicos, açúcares, aminoácidos, glicina betaína e prolina, foi de 5,5, 6, 4 e 0,03%, respectivamente. As folhas de pinhão-manso ajustam-se osmoticamente em presença de salinidade, e mantêm bom nível de hidratação, principalmente por meio da acumulação de Na+ e Cl-. A glicina betaína tem papel quantitativo mais importante do que a prolina no ajustamento osmótico, tanto em presença quanto em ausência de salinidade

Gas exchange and contents of carbohydrates and nitrogen compounds in physic nut irrigated with saline water and wastewater

O objetivo deste trabalho foi avaliar alterações nas trocas gasosas e nos conteúdos de carboidratos e compostos nitrogenados, em pinhão‑manso (Jatropha curcas) irrigado com águas residuária e salina. Empregou‑se o delineamento em blocos ao acaso, com quatro tratamentos e quatro repetições: irrigação plena com água de abastecimento a 0,6 dS m-1 (controle); irrigação plena com água salinizada a 2,4 dS m-1 (SAL); e irrigação com água residuária de esgoto, plena (R100) e a 50% da capacidade de campo (R50). O tratamento R50 reduziu fortemente as trocas gasosas e a área foliar, comparado ao controle, seguido pelos tratamentos SAL e R100. A redução na fotossíntese diminuiu o nível de sacarose nas folhas, nos quatro tratamentos. Os teores de açúcares solúveis aumentaram nos tratamentos R50, SAL e R100, enquanto o conteúdo de amido permaneceu praticamente inalterado. Os conteúdos de prolina e glicina betaína aumentaram nos três tratamentos, mas a última foi mais importante, em termos quantitativos, como protetor celular e osmótico. A irrigação plena com água residuária induz efeitos similares aos causados pela irrigação com água salina. A irrigação limitada com água residuária causa estresse agudo às plantas, provavelmente pela combinação de deficiência hídrica e acúmulo de solutos no solo.The objective of this work was to evaluate the changes in gas exchange and in the contents of carbohydrates and nitrogen compounds in physic nut (Jatropha curcas) irrigated with wastewater and saline water. The experiment was carried out in a randomized block design, with four treatments and four replicates: irrigation with tap water at 0.6 dS m-1 (control); full irrigation with saline tap water at 2.4 dS m-1 (Salt); and irrigation with wastewater at full (W100) or at 50% field capacity (W50). The W50 treatment remarkably reduced gas exchange and leaf area in comparison to the control, followed by Salt and W100 treatments. Reduction in photosynthesis lowered leaf‑sucrose content in the four treatments. Total soluble sugar contents increased in W50, Salt, and W100 treatments, while starch content remained almost unaltered. Proline and glycine betaine contents increased in these treatments, but the latter was quantitatively more important as osmotic and cellular protector. Full irrigation with wastewater induces similar effects to the ones caused by irrigation with saline water. Irrigation with limited amounts of wastewater caused an acute stress to plants, probably due to a combination of water deficit and solute accumulation in the soil

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

Dissipation of excess photosynthetic energy contributes to salinity tolerance: A comparative study of salt-tolerant Ricinus communis and salt-sensitive Jatropha curcas

The relationships between salt tolerance and photosynthetic mechanisms of excess energy dissipation were assessed using two species that exhibit contrasting responses to salinity, Ricinus communis (tolerant) and Jatropha curcas (sensitive). The salt tolerance of R. communis was indicated by unchanged electrolyte leakage (cellular integrity) and dry weight in leaves, whereas these parameters were greatly affected in J. curcas. The leaf Na+ content was similar in both species. Photosynthesis was intensely decreased in both species, but the reduction was more pronounced in J. curcas. In this species biochemical limitations in photosynthesis were more prominent, as indicated by increased Ci values and decreased Rubisco activity. Salinity decreased both the Vcmax (in vivo Rubisco activity) and Jmax (maximum electron transport rate) more significantly in J. curcas. The higher tolerance in R. communis was positively associated with higher photorespiratory activity, nitrate assimilation and higher cyclic electron flow. The high activity of these alternative electron sinks in R. communis was closely associated with a more efficient photoprotection mechanism. In conclusion, salt tolerance in R. communis, compared with J. curcas, is related to higher electron partitioning from the photosynthetic electron transport chain to alternative sinks

Salt stress induced damages on the photosynthesis of physic nut young plants

Salinity is a major limiting factor to crop productivity in the world especially in semiarid regions. The aim of this study was to evaluate the photosynthetic resistance of Jatropha curcas (L.) young plants subjected to salt stress. The experiment was carried out in a completely randomized design with treatments in a 2 x 3 factorial: two NaCl levels (0 and 100 mmol L-1) and three harvest times: 7 and 14 days of salt exposure and three days of recovery. Leaf Na+ and Cl-concentrations and the K+/Na+ ratios, after seven days of salt exposure, did not reach ionic toxic levels, suggesting that the NaCl-induced osmotic effects prevailed over the ionic ones. Under this condition, the salt stress caused reduction in leaf gas exchange parameters, such as CO2 fixation, stomatal conductance and transpiration. In contrast, salt stress did not change the photochemical efficiency of photossystem II. Conversely, after 14 days of treatment, Na+ and Clions reached very high concentrations, up to toxic levels in leaves. Under such conditions, both leaf gas exchange and photochemistry suffered strong impairment probably caused by ionic toxicity. The recovery treatment for 3d did not significantly decrease the leaf salt concentrations and no improvement was observed in the photosynthetic performance. Physic nut young plants are sensitive to high NaCl-salinity conditions, with high leaf Na+ and Cl- concentrations, low K+/Na+ ratio and great photosynthetic damages due to stomatal and biochemical limitations

Mitochondrial glutathione peroxidase (OsGPX3) has a crucial role in rice protection against salt stress

Rice is one of the world's most important crops and an excellent model system for understanding the interaction between genes and environmental changes. However, its productivity is often challenged by abiotic stresses, which results in the accumulation of reactive oxygen species. Glutathione peroxidases are part of the mechanism by which plants face oxidative stress. These enzymes can control redox homeostasis and also play a role in redox signaling. Here, we investigate the role of rice GPX3 in plant responses to salt stress using OsGPX3-RNAi silenced rice plants (GPX3s). Our results indicate that GPX3s plants are more sensitive to salinity showing decreased biomass, CO 2 assimilation rate, stomatal conductance, and intercellular CO 2 partial pressure. Moreover, these plants present significant damage to photosystem II activity and decline in chlorophyll content. Salt stress induced ROS accumulation in both non-transformed (NT) and GPX3s plants, indicating that GPX3s sensibility to salt stress was not due to the significant impairment in redox equilibrium. Together, these results show GPX3 importance in rice to achieve salt stress tolerance via an independent ROS-scavenger mechanism. Moreover, it also provides new light into the cross-talk between chloroplasts and mitochondria, suggesting a novel role to this enzyme beyond its role as ROS-scavenger

Trocas gasosas e conteúdo de carboidratos e compostos nitrogenados em pinhão-manso irrigado com águas residuária e salina

O objetivo deste trabalho foi avaliar alterações nas trocas gasosas e nos conteúdos de carboidratos e compostos nitrogenados, em pinhão-manso (Jatropha curcas) irrigado com águas residuária e salina. Empregou-se o delineamento em blocos ao acaso, com quatro tratamentos e quatro repetições: irrigação plena com água de abastecimento a 0,6 dS m-1 (controle); irrigação plena com água salinizada a 2,4 dS m-1 (SAL); e irrigação com água residuária de esgoto, plena (R100) e a 50% da capacidade de campo (R50). O tratamento R50 reduziu fortemente as trocas gasosas e a área foliar, comparado ao controle, seguido pelos tratamentos SAL e R100. A redução na fotossíntese diminuiu o nível de sacarose nas folhas, nos quatro tratamentos. Os teores de açúcares solúveis aumentaram nos tratamentos R50, SAL e R100, enquanto o conteúdo de amido permaneceu praticamente inalterado. Os conteúdos de prolina e glicina betaína aumentaram nos três tratamentos, mas a última foi mais importante, em termos quantitativos, como protetor celular e osmótico. A irrigação plena com água residuária induz efeitos similares aos causados pela irrigação com água salina. A irrigação limitada com água residuária causa estresse agudo às plantas, provavelmente pela combinação de deficiência hídrica e acúmulo de solutos no solo

Exogenous Sucrose Supply Changes Sugar Metabolism And Reduces Photosynthesis Of Sugarcane Through The Down-regulation Of Rubisco Abundance And Activity.

Photosynthetic modulation by sugars has been known for many years, but the biochemical and molecular comprehension of this process is lacking. We studied how the exogenous sucrose supplied to leaves could affect sugar metabolism in leaf, sheath and stalk and inhibit photosynthesis in four-month old sugarcane plants. Exogenous sucrose 50mM sprayed on attached leaves strongly impaired the net CO2 assimilation (PN) and decreased the instantaneous carboxylation efficiency (PN/Ci), suggesting that the impairment in photosynthesis was caused by biochemical restrictions. The photosystem II activity was also affected by excess sucrose as indicated by the reduction in the apparent electron transport rate, effective quantum yield and increase in non-photochemical quenching. In leaf segments, sucrose accumulation was related to increases in the activities of soluble acid and neutral invertases, sucrose synthase and sucrose phosphate synthase, whereas the contents of fructose increased and glucose slightly decreased. Changes in the activities of sucrose hydrolyzing and synthesizing enzymes in leaf, sheath and stalk and sugar profile in intact plants were not enough to identify which sugar(s) or enzyme(s) were directly involved in photosynthesis modulation. However, exogenous sucrose was able to trigger down-regulation in the Rubisco abundance, activation state and enzymatic activity. Despite the fact that PN/Ci had been notably decreased by sucrose, in vitro activity and abundance of PEPCase did not change, suggesting an in vivo modulation of this enzyme. The data reveal that sucrose and/or other derivative sugars in leaves inhibited sugarcane photosynthesis by down-regulation of Rubisco synthesis and activity. Our data also suggest that sugar modulation was not exerted by a feedback mechanism induced by the accumulation of sugars in immature sugarcane stalk.179113-12