Flavonols protect Arabidopsis plants against UV-B deleterious effects

Flavonols are synthesized by flavonol synthase (FLS) enzymes (Martens et al., 2010). These compounds absorb UV-B light in the 280?320 nm region, and their concentration increases in plants exposed to environmental abiotic and biotic stresses, including UV-B; consequently, flavonols are thought to act as UV-B filters (Agati et al., 2011). It has been also suggested that these metabolites function as reactive oxygen species (ROS) scavengers, as they contain an OH- group in the 3-position of the flavonoid skeleton, which allows them to chelate metals, inhibiting the formation of free radicals and ROS accumulation, once formed (Agati et al., 2009). For these reasons, it has been suggested that flavonols play uncharacterized roles in UV responses (Verdan et al., 2011). Nevertheless, despite the fact that the role of flavonols in UV-B protection has been inferred; the protection conferred by flavonols on the target sites of UV-B-damage has not been directly proven in planta. Recently, we demonstrated that maize FLS1 (ZmFLS1) complements the flavonol deficiency of the Arabidopsis fls1 mutant and decreases its high level of anthocyanins, characteristic of this mutant plant (Falcone Ferreyra et al., 2010). In order to demonstrate that flavonols protect plants against UV-B damage, we generated Arabidopsis transgenic plants overexpressing the maize FLS1 cDNA (35S:ZmFLS1), and evaluated different responses of these transgenic plants against UV-B damage.Fil: Emiliani, Julia.Fil: Grotewold, Erich.Fil: Falcone Ferreyra, María Lorena.Fil: Casati, Paula

Evaluation of cadmium bioaccumulation-related physiological effects in salvinia biloba:An insight towards its use as pollutant bioindicator in water reservoirs

Free-living macrophytes play an important role in the health of aquatic ecosystems. Therefore, the use of aquatic plants as metal biomonitors may be a suitable tool for the management of freshwater reservoirs. Hence, in this study, we assessed the effects of cadmium (Cd) in Salvinia biloba specimens collected from the Middle Paraná River during a 10-day experiment employing artificially contaminated water (100 μM Cd). S. biloba demonstrated a great ability for Cd bioaccumulation in both the root-like modified fronds (named “roots”) and the aerial leaf-like fronds (named “leaves”) of the plants. Additionally, Cd toxicity was determined by the quantification of photosynthetic pigments (chlorophylls a and b, and carotenoids), flavonoids, and soluble carbohydrate contents in S. biloba over time (1, 3, 5, 7, and 10 days). In general, deterioration was more pronounced in leaves than in roots, suggesting a greater implication of the former in long-term Cd sequestration in S. biloba. Deleterious effects in the appraised parameters were well correlated with the total amount of Cd accumulated in the leaves, and with the qualitative changes observed in the plants’ phenotype during the 10-day metal exposure assay. The flavonoids and carotenoids in leaves were highly affected by low Cd levels followed by root carbohydrates. In contrast, chlorophylls and root flavonoids were the least impacted physiological parameters. Therefore, our results demonstrate that S. biloba displays dissimilar organ-linked physiological responses to counteract Cd phytotoxicity and that these responses are also time-dependent. Though further research is needed, our work suggests that easy-handled physiological data obtained from autochthonous free-floating S. biloba specimens may be used as a valuable tool for metal-polluted water biomonitoring

Effect of daily exposure to Pb-contaminated water on Salvinia biloba physiology and phytoremediation performance

Lead (Pb) removal from water column was evaluated in batch experiments using naturally occurring Salvinia biloba Raddi (S. biloba) specimens collected from Middle Parana River and exposed every 24 h to a fresh discharge of water contaminated with 2.65 ± 0.07, 12.62 ± 0.02 or 30.57 ± 0.01 mg L−1 Pb, during 10 consecutive days. S. biloba demonstrated a great ability for metal concentration-dependent Pb removal under these stressful conditions. Additionally, Pb toxicity in plants was assessed by the quantification of physiological parameters in root-like modified fronds (named “roots”), and its aerial leaf-like fronds (named “leaves”) of submerged S. biloba. Photosynthetic (carotenoids, chlorophyll a, b, and total) and antioxidant pigments (anthocyanins and flavonoids), soluble carbohydrate content, and membrane stability index of both roots and leaves were affected as the metal concentration increased. In general, root deterioration was more pronounced than that in leaves, suggesting a greater implication of the former organs in Pb removal by S. biloba. All of these deleterious effects were well correlated with qualitative changes observed at plant phenotype during the assay. In conclusion, S. biloba may be considered as a water fern useful in phytoremediation strategies towards management of residual water bodies contaminated with Pb. In addition, these macrophytes could also be valuable for water biomonitoring contributing to improve risk assessments related to metal presence in wastewaters.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

A role for β,β-xanthophylls in Arabidopsis UV-B photoprotection

Plastidial isoprenoids, such as carotenoids and tocopherols, are important anti-oxidant metabolites synthesized in plastids from precursors generated by the methylerythritol 4-phosphate (MEP) pathway. In this study, we found that irradiation of Arabidopsis thaliana plants with UV-B caused a strong increase in the accumulation of the photoprotective xanthophyll zeaxanthin but also resulted in slightly higher levels of γ-tocopherol. Plants deficient in the MEP enzymes 1-deoxy-D-xylulose 5-phosphate synthase and 1-hydroxy-2-methyl-2-butenyl 4-diphosphate synthase showed a general reduction in both carotenoids and tocopherols and this was associated with increased DNA damage and decreased photosynthesis after exposure to UV-B. Genetic blockage of tocopherol biosynthesis did not affect DNA damage accumulation. In contrast, lut2 mutants that accumulate β,β-xanthophylls showed decreased DNA damage when irradiated with UV-B. Analysis of aba2 mutants showed that UV-B protection was not mediated by ABA (a hormone derived from β,β-xanthophylls). Plants accumulating β,β-xanthophylls also showed decreased oxidative damage and increased expression of DNA-repair enzymes, suggesting that this may be a mechanism for these plants to decrease DNA damage. In addition, in vitro experiments also provided evidence that β,β-xanthophylls can directly protect against DNA damage by absorbing radiation. Together, our results suggest that xanthophyll-cycle carotenoids that protect against excess illumination may also contribute to protection against UV-B

Estudio del rol de distintas enzimas que participan en la vía de síntesis de flavonoides en la respuesta a la radiación UV-B en plantas

Los flavonoides son metabolitos secundarios con diversas funciones biológicas, distribuidos de forma ubicua en el reino vegetal. Formas primitivas de estos compuestos posiblemente acompañaron la adaptación de las plantas a la superficie de la Tierra. En particular, un subgrupo de estos metabolitos, los flavonoles, participan en la regulación del transporte de auxinas y son esenciales para la macho esterilidad en algunas especies vegetales. En este trabajo de Tesis, la utilización de plantas transgénicas de Arabidopsis thaliana con mayores niveles de flavonoles, permitió demostrar mediante experimentos de acumulación de daño en el ADN, actividad fotosintética, daño a las membranas e inhibición de la elongación de la raíz primaria luego de un tratamiento con UV-B, que estos metabolitos cumplen roles protectores en las plantas frente a un tipo de estrés abiótico como la radiación UV-B; ejercido como efectivos filtros UV-B y/o debido a sus propiedades antioxidantes. Otro subgrupo de flavonoides se encuentra constituido por las flavonas producidas a partir de las flavanonas. En este trabajo de Tesis, mediante la expresión recombinante en sistemas heterólogos y análisis de LCMS, se logró caracterizar por primera vez en maíz, dos enzimas con capacidad de sintetizar flavonas; una de ellas caracterizada como una flavanona 2-hidroxilasa (ZmF2H1) y la otra, como una enzima flavona sintasa I (ZmFNSI-1). Además, fue posible también demostrar que una especie Brasicácea como Arabidopsis contiene en su genoma un gen codificante a una enzima FNSI (AtFNSI-1) con capacidad de producir flavonas con un rol no identificado hasta el momento frente al ataque del patógeno oomicete Hyaloperonospora parasítica, un hecho nunca antes visto en esta especie vegetal.Fil: Emiliani, Julia. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI-CONICET); Argentina

Evaluation of Cadmium Bioaccumulation-Related Physiological Effects in Salvinia biloba: An Insight towards Its Use as Pollutant Bioindicator in Water Reservoirs

Free-living macrophytes play an important role in the health of aquatic ecosystems. Therefore, the use of aquatic plants as metal biomonitors may be a suitable tool for the management of freshwater reservoirs. Hence, in this study, we assessed the effects of cadmium (Cd) in Salvinia biloba specimens collected from the Middle Paraná River during a 10-day experiment employing artificially contaminated water (100 μM Cd). S. biloba demonstrated a great ability for Cd bioaccumulation in both the root-like modified fronds (named “roots”) and the aerial leaf-like fronds (named “leaves”) of the plants. Additionally, Cd toxicity was determined by the quantification of photosynthetic pigments (chlorophylls a and b, and carotenoids), flavonoids, and soluble carbohydrate contents in S. biloba over time (1, 3, 5, 7, and 10 days). In general, deterioration was more pronounced in leaves than in roots, suggesting a greater implication of the former in long-term Cd sequestration in S. biloba. Deleterious effects in the appraised parameters were well correlated with the total amount of Cd accumulated in the leaves, and with the qualitative changes observed in the plants’ phenotype during the 10-day metal exposure assay. The flavonoids and carotenoids in leaves were highly affected by low Cd levels followed by root carbohydrates. In contrast, chlorophylls and root flavonoids were the least impacted physiological parameters. Therefore, our results demonstrate that S. biloba displays dissimilar organ-linked physiological responses to counteract Cd phytotoxicity and that these responses are also time-dependent. Though further research is needed, our work suggests that easy-handled physiological data obtained from autochthonous free-floating S. biloba specimens may be used as a valuable tool for metal-polluted water biomonitoring

P1 epigenetic regulation in leaves of high altitude maize landraces: effect of UV-B radiation

P1 is a R2R3-MYB transcription factor that regulates the accumulation of a specific group of flavonoids in maize floral tissues, such as flavones and phlobaphenes. P1 is also highly expressed in leaves of maize landraces adapted to high altitudes and higher levels of UV-B radiation. In this work, we analyzed the epigenetic regulation of the P1 gene by UV-B in leaves of different maize landraces. Our results demonstrate that DNA methylation in the P1 proximal promoter, intron1 and intron2 is decreased by UV-B in all lines analyzed; however, the basal DNA methylation levels are lower in the landraces than in B73, a low altitude inbred line. DNA demethylation by UV-B is accompanied by a decrease in H3 methylation at Lys 9 and 27, and by an increase in H3 acetylation. smRNAs complementary to specific regions of the proximal promoter and of intron 2 3 ′ end are also decreased by UV-B; interestingly, P1 smRNA levels are lower in the landraces than in B73 both under control conditions and after UV-B exposure, suggesting that smRNAs regulate P1 expression by UV-B in maize leaves. Finally, we investigated if different P1 targets in flower tissues are also regulated by this transcription factor in response to UV-B. Some targets analyzed show an induction in maize landraces in response to UV-B, with higher basal expression levels in the landraces than in B73; however, not all the transcripts analyzed were found to be regulated by UV-B in leaves.Para citar este articulo: Rius SP, Emiliani J and Casati P (2016) P1 Epigenetic Regulation in Leaves of High Altitude Maize Landraces: Effect of UV-B Radiation. Front. Plant Sci. 7:523. doi: 10.3389/fpls.2016.00523Fil: Rius, Sebastián P. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI -CONICET); Argentina.Fil: Emiliani, Julia. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI -CONICET); Argentina.Fil: Casati, Paula. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI -CONICET); Argentina