Publications

Abstract Marine Coelenterazine is one of the most well-known chemi-/bioluminescent systems, and in which reaction the chemi-/bioluminophore (Coelenteramide) is generated and chemiexcited to singlet excited states (leading to light emission). Recent studies have shown that the bromination of compounds associated with the marine Coelenterazine system can provide them with new properties, such as anticancer activity and enhanced emission. Given this, our objective is to characterize the photophysical properties of a previously reported brominated Coelenteramide analog, by employing a combined experimental and theoretical approach. To better analyze the potential halogen effect, we have also synthesized and characterized, for the first time, two new fluorinated and chlorinated Coelenteramide analogs. These compounds show similar emission spectra in aqueous solution, but with different fluorescence quantum yields, in a trend that can be correlated with the heavy-atom effect (F > Cl > Br). A blue shift in emission in other solvents is also verified with the F-Cl-Br trend. More relevantly, the fluorescence quantum yield of the brominated analog is particularly sensitive to changes in solvent, which indicates that this compound has potential use as a microenvironment fluorescence probe. Theoretical calculations indicate that the observed excited state transitions result from local excitations involving the pyrazine ring. The obtained information should be useful for the further exploration of halogenated Coelenteramides and their luminescent properties.

Abstract Currently, salinity and heat are two critical threats to crop production and food security which are being aggravated by the global climatic instability. In this scenario, it is imperative to understand plant responses to simultaneous exposure to different stressors and the cross-talk between underlying functional mechanisms. Thus, in this study, the physiological and biochemical responses of tomato plants (Solanum lycopersicum L.) to the combination of salinity (100 mM NaCl) and heat (42 degrees C; 4 h/day) stress were evaluated. After 21 days of co-exposure, the accumulation of Na+ in plant tissues was superior when salt-treated plants were also exposed to high temperatures compared to the individual saline treatment, leading to the depletion of other nutrients and a harsher negative effect on plant growth. Despite that, neither oxidative damage nor a major accumulation of reactive oxygen species took place under stress conditions, mostly due to the accumulation of antioxidant (AOX) metabolites alongside the activation of several AOX enzymes. Nonetheless, the plausible allocation of resources towards the defense pathways related to oxidative and osmotic stress, along with severe Na toxicity, heavily compromised the ability of plants to grow properly when the combination of salinity and heat was imposed.

Abstract Aluminum (Al) toxicity limits crops growth and production in acidic soils. Compared to roots, less is known about the toxic effects of Al in leaves. Al subcellular compartmentalization is also largely unknown. Using rye (Secale cereale L.) Beira (more tolerant) and RioDeva (more sensitive to Al) genotypes, we evaluated the patterns of Al accumulation in leaf cell organelles and the photosynthetic and metabolic changes to cope with Al toxicity. The tolerant genotype accumulated less Al in all organelles, except the vacuoles. This suggests that Al compartmentalization plays a role in Al tolerance of Beira genotype. PSII efficiency, stomatal conductance, pigment biosynthesis, and photosynthesis metabolism were less affected in the tolerant genotype. In the Calvin cycle, carboxylation was compromised by Al exposure in the tolerant genotype. Other Calvin cycle-related enzymes, phoshoglycerate kinase (PGK), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), triose-phosphate isomerase (TPI), and fructose 1,6-bisphosphatase (FBPase) activities decreased in the sensitive line after 48 h of Al exposure. Consequentially, carbohydrate and organic acid metabolism were affected in a genotype-specific manner, where sugar levels increased only in the tolerant genotype. In conclusion, Al transport to the leaf and compartmentalization in the vacuoles tolerant genotype's leaf cells provide complementary mechanisms of Al tolerance, protecting the photosynthetic apparatus and thereby sustaining growth.

Abstract Purpose Soil is a complex open system covering various physical and chemical attributes. In soil testing, multivariate analysis (MVA) has an important application because it allows the interpretation of a large amount of data for the design of relevant environmental scenarios. The purpose of this research is to summarize recent applications of MVA for identifying soil types or characteristics and for predicting soil attributes with a critical evaluation. Methods Based on a comprehensive search of the available database, in this review, we have provided updated information on the most representative classification and regression MVA applied in the past decade in soil surveys. Regression MVA were compared in terms of applicability, efficiency, and predictive power of different soil attributes. Results Principal component analysis (PCA) allows the grouping of soils into independent clusters according to their differences in texture or physicochemical composition, which may mirror local or regional environmental signatures. PCA is also used to reduce the dimensionality of spectral data before their application in regression MVA. Partial least square regression (PLSR) is the most commonly applied regression MVA for predicting soil attributes after the correlation of spectra (e.g., Vis-NIR) vs. conventional analysis results. The resulting PLSR models, evaluated by correlation coefficient (R-2) and root mean squared error (RMSE), can be valid for the estimation of several soil attributes (e.g., organic carbon, clay). Conclusions Application of regression MVA may have limitations in predicting some soil attributes. Objective interpretation of the dynamic nature of soils requires the selection of representative samples as well as appropriate MVA, which can have significant potential in an effective soil survey.

Abstract Since metal contamination compromises crop growth and food safety, eco-friendly responses to prevent this are needed. This study provided an integrative evaluation of the potential of wrack (macroalgae debris) to increase the tolerance of Hordeum vulgare L. (barley plant) to copper (Cu).Plants were grown in a soil mixed with 219 mg Cu kg(-1) with/without 2% (m/m) wrack for 14 days. Copper impaired all growth-related parameters. Wrack application counteracted most of these negative impacts and lowered metal accumulation in roots. Metal exposure increased reactive oxygen species content [superoxide anion (O-2(center dot-)) and hydrogen peroxide [H2O2]) and lipid peroxidation degree, which was evaluated through the quantification of malondialdehyde, while co-treatment with wrack partially reverted some of these effects. The non-enzymatic antioxidant (AOX) system was mainly activated by Cu, with accumulated glutathione (GSH), ascorbate (AsA) and phenols, mostly in roots, while proline content was reduced. Wrack protective action was through a modulation of GSH and AsA redox state and enhanced ascorbate peroxidase. The results suggest wrack's potential to alleviate Cu-induced phytotoxicity, which probably relies on the reduction of Cu-induced oxidative stress through a more efficient activity of AOX metabolites and by limiting Cu absorption and bioaccumulation, especially in roots of barley plants.

Abstract Plant biostimulants such as seaweed extracts, present a sustainable alternative to agrochemicals. Moreover, the accumulation of beach-cast seaweed (wrack), due to climate change and anthropic pressures, is expected to increase in the coming decades. Thus, from a perspective of circular economy, based on the valorisation of an organic residue, this study aimed at achieving an elemental and biochemical characterisation of beach wrack and understanding the effects of an aqueous extract prepared from this residue on the mitigation of metal-induced stress, using barley (Hordeum vulgare L.) as a model. The quantification of wrack's macro- and micronutrients showed that K, Ca and Na were the most abundant elements, being this composition similar to that of other organic fertilisers. Furthermore, despite the studied wrack having lower values of photosynthetic pigments, amino acids and sugars, higher amounts of phenols and flavonoids (8.35 +/- 0.24 and 3.95 +/- 1.22 mg g(-1) dry matter respectively) were detected when compared to freshly collected seaweeds. This work highlighted that wrack showed potential as a fertiliser-through increasing root biomass (63%) and leaf biometry (up to 45%) in plants treated with 5.0 and 7.5 g L-1 wrack extract alone-also being a possible cost-effective, eco-friendly and sustainable biostimulant to mitigate the phytotoxic effects of Cu, since plants treated with 7.5 g wrack L-1 showed an increase of 34% in leaf length, when compared to seedlings exposed only to Cu.