Bioaccumulation and physiological traits qualify Pistia stratiotes as a suitable species for phytoremediation and bioindication of iron-contaminated water.

Serious concerns have recently been raised regarding the association of Fe excess with neurodegenerative diseases in mammals and nutritional and oxidative disorders in plants. Therefore, the current study aimed to understand the physiological changes induced by Fe excess in Pistia stratiotes, a species often employed in phytoremediation studies. P. stratiotes were subjected to five concentrations of Fe: 0.038 (control), 1.0, 3.0, 5.0 and 7.0 mM. Visual symptoms of Fe-toxicity such as bronzing of leaf edges in 5.0 and 7.0 mM-grown plants were observed after 5 days. Nevertheless, no major changes were observed in photosynthesis-related parameters at this time-point. In contrast, plants growing for 10 days in high Fe concentrations showed decreased chlorophyll concentrations and lower net CO2 assimilation rate. Notwithstanding, P. stratiotes accumulated high amounts of Fe, especially in roots (maximum of 10,000 µg g-1 DW) and displayed a robust induction of the enzymatic antioxidant system. In conclusion, we demonstrated that P. stratiotes can be applied to clean up Fe-contaminated water, as the species displays high Fe bioaccumulation, mostly in root apoplasts, and can maintain physiological processes under Fe excess. Our results further revealed that by monitoring visual symptoms, P. stratiotes could be applied for bioindication purposes.

Mitochondrial and peroxisomal NAD+ uptake are important for improved photosynthesis and seed yield under elevated CO2 concentrations.

As sessile organisms, plants must adapt their physiology and developmental processes to cope with challenging environmental circumstances, such as the ongoing elevation in atmospheric carbon dioxide (CO2 ) levels. Nicotinamide adenine dinucleotide (NAD+ ) is a cornerstone of plant metabolism and plays an essential role in redox homeostasis. Given that plants impaired in NAD metabolism and transport often display growth defects, low seed production and disturbed stomatal development/movement, we hypothesized that subcellular NAD distribution could be a candidate for plants to exploit the effects of CO2 fertilization. We report that an efficient subcellular NAD+ distribution is required for the fecundity-promoting effects of elevated CO2 levels. Plants with reduced expression of either mitochondrial (NDT1 or NDT2) or peroxisomal (PXN) NAD+ transporter genes grown under elevated CO2 exhibited reduced total leaf area compared with the wild-type while PXN mutants also displayed reduced leaf number. NDT2 and PXN lines grown under elevated CO2 conditions displayed reduced rosette dry weight and lower photosynthetic rates coupled with reduced stomatal conductance. Interestingly, high CO2 doubled seed production and seed weight in the wild-type, whereas the mutants were less responsive to increases in CO2 levels during reproduction, producing far fewer seeds than the wild-type under both CO2 conditions. These data highlight the importance of mitochondrial and peroxisomal NAD+ uptake mediated by distinct NAD transporter proteins to modulate photosynthesis and seed production under high CO2 levels.

New insights into molecular targets of salt tolerance in sorghum leaves elicited by ammonium nutrition.

This study investigated the proteome modulation and physiological responses of Sorghum bicolor plants grown in nutrient solutions containing nitrate (NO3-) or ammonium (NH4+) at 5.0 mM, and subjected to salinity with 75 mM NaCl for ten days. Salinity promoted significant reductions in leaf area, root and shoot dry mass of sorghum plants, regardless of nitrogen source; however, higher growth was observed in ammonium-grown plants. The better performance of ammonium-fed stressed plants was associated with low hydrogen peroxide accumulation, and improved CO2 assimilation and K+/Na+ homeostasis under salinity. Proteomic study revealed a nitrogen source-induced differential modulation in proteins related to photosynthesis/carbon metabolism, energy metabolism, response to stress and other cellular processes. Nitrate-fed plants induced thylakoidal electron transport chain proteins and structural and carbon assimilation enzymes, but these mechanisms seemed to be insufficient to mitigate salt damage in photosynthetic performance. In contrast, the greater tolerance to salinity of ammonium-grown plants may have arisen from: i.) de novo synthesis or upregulation of enzymes from photosynthetic/carbon metabolism, which resulted in better CO2 assimilation rates under NaCl-stress; ii.) activation of proteins involved in energy metabolism which made available energy for salt responses, most likely by proton pumps and Na+/H+ antiporters; and iii.) reprogramming of proteins involved in response to stress and other metabolic processes, constituting intricate pathways of salt responses. Overall, our findings not only provide new insights of molecular basis of salt tolerance in sorghum plants induced by ammonium nutrition, but also give new perspectives to develop biotechnological strategies to generate more salt-tolerant crops.

Evaluation of Metals in Soil and Tissues of Economic-Interest Plants Grown in Sites Affected by the Fundão Dam Failure in Mariana, Brazil.

The objective of this study was to evaluate the concentration of potentially toxic elements in Brachiaria decumbens, Stylosanthes guianensis, and Saccharum officinarum plants and soil samples in affected and unaffected areas by rupture of the Fundão dam, Brazil. Samples were collected in areas affected by residues from the Fundão dam (RAA1, RAA2, RAA3) and in an unaffected area (control). The material was analyzed for the composition of micronutrients and trace elements in soil and plants, as well as contamination factor (CF), accumulation factor, and translocation factor (TF). Overall, the results showed that soil and plant tissues had increased Fe, Mn, Cu, and Cr content and decreased Zn content in the affected areas, compared to the control. Leaves and roots of B. decumbens showed an increase in Fe content in affected areas, compared to the control, reaching a mean maximum value of 42 958 µg/g of roots of RAA2-collected plants. As a result, CF for Fe of B. decumbens was classified as very high and they presented low TF values. Furthermore, B. decumbens collected in affected areas showed an increase of Fe, Mn, Cu, and Cr in leaves, stems, and roots, whereas in Stylosanthes guianensis, there was an increase of Fe concentration in all tissues and Cr in leaves. Also, Saccharum officinarum showed the accumulation of Mn in the stem and Cu in leaves and stem. On the other hand, there was no contamination of plants by hazardous elements such as Pb, Cd, and As in the samples analyzed. In conclusion, increases in the content of Fe, Mn, Cu, and Cr were found in soil and several plant tissues of residue-affected areas, which could compromise plant growth and represent potential hazards arising from the biomagnification process in the food chain. Integr Environ Assess Manag 2020;16:596-607. © 2020 SETAC.

O objetivo deste estudo foi avaliar a concentração de elementos potencialmente tóxicos em plantas de Brachiaria decumbens, Stylosanthes guianensis e Saccharum officinarum e amostras de solos em áreas afetadas e não afetadas pelo rompimento da barragem de Fundão. As amostras foram coletadas em áreas afetadas por resíduos da barragem de Fundão (RAA1, RAA2, RAA3) e em uma área não afetada (controle). O material foi analisado quanto à composição de micronutrientes e elementos-traço no solo e plantas, além de fatores de contaminação (CF), bioacumulação e translocação (TF). No geral, os resultados mostraram que o solo e as plantas apresentaram maiores teores de Fe, Mn, Cu e Cr e menores teores de Zn nas áreas afetadas em comparação ao controle. Folhas e raízes de B. decumbens apresentaram aumento no teor de Fe nas áreas afetadas em relação ao controle, atingindo o valor máximo médio de 42.958 µg/g nas raízes de plantas coletadas em RAA2. Como resultado, CF para Fe de B. decumbens foi classificado como muito alto, mas com baixos valores de TF. Além disso, B. decumbens coletadas nas áreas afetadas apresentaram aumento de Fe, Mn, Cu e Cr nas folhas, caules e raízes, enquanto que em Stylosanthes guianensis houve aumento da concentração de Fe em todos as partes das plantas e Cr nas folhas. Saccharum officinarum também apresentou acúmulo de Mn no caule e Cu nas folhas e caule. Por outro lado, não há contaminação das plantas por elementos perigosos como Pb, Cd e As nas amostras analisadas. Concluindo, foram encontrados aumentos nos teores de Fe, Mn, Cu e Cr no solo e em vários tecidos vegetais, o que pode comprometer o crescimento das plantas e representar riscos potenciais decorrentes do processo de biomagnificação na cadeia alimentar. Integr Environ Assess Manag 2020;16:596-607.

Is arsenite more toxic than arsenate in plants?

In order to evaluate the differential absorption and toxicity of arsenate (AsV) and arsenite (AsIII), Lemna valdiviana plants were grown in a nutrient solution and subjected to 0.0 (control); 0.5; 1.0; 1.5; 2.0; 3.0; 4.0; 5.0 and 7.5 mg L-1 of AsIII or AsV for three days. Exposure to both chemical forms resulted in As bioaccumulation, although AsIII-grown plants showed higher As content in tissues. In AsV-grown plants, the relative growth rate (RGR) decreased to 50%, at a concentration of 4.0 mg L-1, while for treatments with AsIII, the same decrease was observed at 1.0 mg L-1. The tolerance index decreased with increasing concentrations, with lower values for AsIII. Plants treated with AsIII showed increased superoxide anion levels, whilst higher levels of hydrogen peroxide were present in AsV-treated plants. Moreover, malondialdehyde (MDA) levels were higher for plants subjected to AsIII when compared to AsV at lower concentrations. Concentrations of 1 mg L-1 of AsIII and 4 mg L-1 of AsV showed equivalent MDA levels. Superoxide dismutase and catalase activities were increased at low concentrations and were inhibited at higher concentrations of AsIII and AsV, whereas peroxidase activity was positively modulated by increased AsIII or AsV concentrations. In conclusion, L. valdiviana plants took up and accumulated arsenic as AsIII or AsV, demonstrating the potential for phytoremediation of this metalloid. Furthermore, AsIII-exposed plants showed enhanced toxicity when compared to AsV, at the same applied concentration, although toxicity was more related to internal As concentrations, regardless of the chemical form applied.

Association of preharvest management with oxidative protection and enzymatic browning in minimally processed cassava.

The aim of this study was to examine oxidative protection and enzymatic browning in the storage of minimally processed cassava and their relationship with population density and harvest age. Population densities were 1.0, 1.25, 1.5, and 1.75 plants m-2 . After being harvested at 300, 360, or 420 days after planting, cassava were minimally processed and stored at 5 ± 2°C. It was observed that superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) play key roles in the tolerance of young roots to browning. Planting density, however, does not appear to be a key factor modulating the activity of the enzymes studied. PRACTICAL APPLICATIONS: Younger harvested cassava roots, harvested at 300 days, are more tolerant to enzymatic browning. This appears to be in part due to enzymatic activity modulation of the SOD, CAT, and POD enzymes. In addition, it has been demonstrated that agronomic techniques aimed at increasing productivity, such as increasing the planting density of cassava, do not alter the biomarkers of postharvest quality. In summary, evidence that field management may be an efficient approach to improving the conservation of minimally processed cassava is provided. We believe that the findings of this paper will be of great interest regarding the influence of field management on the postharvest quality of freshly cut cassava and will also provide applicable results relating to its production chain.

Salt acclimation in sorghum plants by exogenous proline: physiological and biochemical changes and regulation of proline metabolism.

KEY MESSAGE: Mitigation of deleterious effects of salinity promoted by exogenous proline can be partially explained by changes in proline enzymatic metabolism and expression of specific proline-related genes. Proline accumulation is a usual response to salinity. We studied the ability of exogenous proline to mitigate the salt harmful effects in sorghum (Sorghum bicolor) leaves. Ten-day-old plants were cultivated in Hoagland's nutrient solution in either the absence or presence of salinity (NaCl at 75 mM) and sprayed with distilled water or 30 mM proline solution. Salinity deleterious effects were alleviated by exogenous proline 14 days after treatment, with a return in growth and recovery of leaf area and photosynthetic parameters. Part of the salinity response reflected an improvement in ionic homeostasis, provided by reduction in Na+ and Cl- ions and increases in K+ and Ca2+ ions as well as increases of compatible solutes. In addition, the application of proline decreased membrane damage and did not increase relative water content. Proline-treated salt-stressed plants displayed increase in proline content, a response counterbalanced by punctual modulation in proline synthesis (down-regulation of Δ1-pyrroline-5-carboxylate synthetase activity) and degradation (up-regulation of proline dehydrogenase activity) enzymes. These responses were correlated with expression of specific proline-related genes (p5cs1 and prodh). Our findings clearly show that proline treatment results in favorable changes, reducing salt-induced damage and improving salt acclimation in sorghum plants.