Water contamination with atrazine: is nitric oxide able to improve Pistia stratiotes phytoremediation capacity?

Atrazine is an herbicide commonly used in several countries. Due to its long half-life, associated with its use in large scales, atrazine residues remain as environmental pollutants in water bodies. Phytoremediation is often pointed out as an interesting approach to remove atrazine from the aquatic environment, but its practical application is limited by the high toxicity of this herbicide. Here, we characterize the damages triggered by atrazine in Pistia stratiotes, evaluating the role of nitric oxide (NO), a cell-signaling molecule, in increasing the tolerance to the pollutant and the phytoremediation potential of this species. Pistia stratiotes plants were exposed to four treatments: Control; Sodium nitroprusside (SNP) (0.05 mg L-1); Atrazine (ATZ) (150 µg L-1) and ATZ + SNP. The plants remained under those conditions for 24 h for biochemical and physiological analysis and 3 days for the evaluation of relative growth rate. The presence of atrazine in plant cells triggered a series of biochemical and physiological damages, such as the increase in the generation of reactive oxygen species, damages to cell membranes, photosynthesis impairment, and negative carbon balance. Despite this, the plants maintained greater growth rates than other aquatic macrophytes exposed to atrazine and showed high bioconcentration and translocation factors. The addition of SNP, a NO donor, decreased the herbicide toxicity, with an increase of over 60% in the IC50 value (Inhibitor Concentration). Indeed, the NO signaling action was able to increase the tolerance of plants to atrazine, which resulted in increments in pollutant uptake and translocation, with the maintenance of overall cell (e.g. membranes) and organs (root system) structure, and the functioning of central physiological processes (e.g. photosynthesis). These factors allowed for more quickly and efficient removal of the pollutant from the environment, reducing costs, and increasing the viability of the phytoremediation process.

Evidence of drought memory in Dipteryx alata indicates differential acclimation of plants to savanna conditions.

The remarkable phytogeographic characteristics of the Brazilian savanna (Cerrado) resulted in a vegetation domain composed of plants with high structural and functional diversity to tolerate climate extremes. Here we used a key Cerrado species (Dipteryx alata) to evaluate if species of this domain present a mechanism of stress memory, responding more quickly and efficiently when exposed to recurrent drought episodes. The exposure of D. alata seedlings to drought resulted in several changes, mainly in physiological and biochemical traits, and these changes differed substantially when the water deficit was imposed as an isolated event or when the plants were subjected to drought cycles, suggesting the existence of a drought memory mechanism. Plants submitted to recurrent drought events were able to maintain essential processes for plant survival when compared to those submitted to drought for the first time. This differential acclimation to drought was the result of orchestrated changes in several metabolic pathways, involving differential carbon allocation for defense responses and the reprogramming and coordination of primary, secondary and antioxidant metabolism. The stress memory in D. alata is probably linked the evolutionary history of the species and reflects the environment in which it evolved.