The crucial role of sulfur in a phytoremediation process : Lessons from the Poaceae species as phytoremediants : a review

Among living organisms plants are the most tolerant to pollution. This fact, emphasizes their utility for phytoremediation, a promising technology for environmental cleanup. Many botanical families include multiple species which exhibit a notable phytoremediation potential. Each of these species enjoys certain advantages, but at the same encounters some limitations with respect to its application as phytoremediants. Careful selection of the appropriate family and genotype to match the particular pollutant and environment is crucial for successful phytoremediation; the Poaceae family seems to be one of the most important for this technology. Phytoremediation of inorganic and organic pollutants largely depends on sulfur (S) metabolism. Therefore, S sufficient conditions and efficient S metabolism constitute the prerequisites for the effectiveness of the process. In the modern societies, heavy-metal pollution of soils is causing ever greater problems, exacerbated by the fact that most heavy metals accumulated in plants may, either directly or indirectly, find their way into animals and human beings. Wheat, rice and maize are among the world\u2019s most prominent crops, whilst cadmium (Cd) and nickel (Ni) are among the most toxic metals. Therefore, the physiological adaptations induced in cereals, by Cd for example, are alarming and subsequently, the responsiveness of these species has been studied extensively as model plants. Studies with Arundo donax as phytoremediant have proven that this species is tolerant to increased concentrations of Cd and Ni in its rhizosphere, and as a consequence, it can be cultivated in contaminated areas for phytoremediation and energy production purposes. S-deficiency of crops is frequently reported, especially during the past two decades, worldwide. The main reasons for this deficiency are: the reduction of sulfur dioxide emission from power plants and various industrial sources, the ever increasing use of high-analysis low-S-containing fertilizers and the decreasing use of S-containing fertilizers, S-containing fungicides, pesticides and high-yielding varieties. A sufficient S supply of cereal crops is required in early growth stages, which cannot be fully compensated by S fertilization during later growth. Elemental S proved to contribute continuously to the crop\u2019s S nutrition due to its constant release after oxidation. Therefore, the early diagnosis of S deficiency, the profiling of S forms in the soil of the phytoremediation site and the prediction of S-fertilizer requirements are of key importance for achieving a successful process

Activity of cell wall-associated enzymes in ripening olive fruit

Enzymatically active cell wall isolaled from olive (Olea europaea) fruit was employed Hi investigate some hydrolytic enzymes bound to the cell wall and the changes in these during ripening. Seven glycosidases. β-glucosidase (EC 3.2.1.21) α-galactosidase (EC 3.2.1.22). β-galactosidase (EC 3.2.1.23). α-arabinosidase (EC 3.2.1.55), α-mannosidase (EC 3.2.1,24). β-xylosidase (EC 3.2.1.37) and β-N-acetylglucosamidase (EC 3.2.1.30). as well as Cx-cellulase (EC 3.2.1.4) and endo-polygalacturonase (EC 3.2.1.15). were identified in the cell wall preparation, at four stages of ripeness (mature green. changing colour, black and black-ripe). Activities of all these cell wall-associated enzymes fionicallv and covalently linked) were determined either by cell wall incubation with artificial substrate or after extraction from the cell wall with buffers of high salt concentration (Cx-cellulase). and were compared to those of forms solubilized from acetone powders with 500 nM citrate buffer (cytoplasmic and/or apoplastic plus ionically hound to cell wall) In general, the activities of low ionic strength buffer-soluble enzymes were found to be much higher than those of the bound enzymes. The bound enzymes are present in the fruit at the green colour stage, whereas the activities of the soluble enzymes only increased from the changing colour stage onwards. The tenacity of binding of enzymes to the wall was investigated by treating the walls with high salt and measuring residual activity. The nature of the ionic and covalent binding and the changes during ripening were also established for wall-hound glycosidase During ripening there was a marked change in the percentages of covalently- and tonically linked activities of β-glucosidase and β-galaclosidase: al the changing colour stages about 75–80% of the bound active in was present in high ionic strength buffer while al the black-ripe stage it was only 15–20. A possible role for these cell wall degradative enzymes in olive softening is discussed.Peer reviewe

Atividade do sistema antioxidante e desenvolvimento de aerênquima em raízes de milho 'Saracura' Antioxidant system activity and aerenchyma formation in 'Saracura' maize roots

Este trabalho teve como objetivo avaliar a influência de sucessivos ciclos de seleção do milho 'Saracura' na atividade das enzimas do sistema antioxidante, e a relação dessas enzimas com a capacidade dessa variedade em desenvolver aerênquima. Sementes de 18 ciclos de seleção intercalados do milho 'Saracura' e da cultivar BR 107, sensível à hipoxia, foram semeadas em vasos e em casa de vegetação. As plantas foram submetidas ao alagamento intermitente de dois em dois dias. As amostras de raízes foram coletadas após 60 dias e analisaram-se as atividades das enzimas peroxidase do guaiacol, peroxidase do ascorbato e catalase, além da capacidade das plantas de cada ciclo desenvolverem aerênquima. Ao longo dos ciclos, as plantas apresentaram modificações na atividade das enzimas, com aumento na de peroxidase do ascorbato e diminuição na de catalase e de peroxidase do guaiacol. Observou-se, ainda, maior capacidade de desenvolver aerênquima nos últimos ciclos de seleção. A redução na atividade das enzimas do sistema antioxidante parece estar relacionada a um desbalanço na decomposição de H2O2.<br>This work aimed to assess the influence of successive selection cycles in 'Saracura' maize on the enzyme activity of the antioxidant system and the relationship of these enzymes with the aerenchyma development capacity of this variety. Seeds of 18 intercalated selection cycles of the 'Saracura' maize and of the cultivar BR 107, sensitive to hipoxia, were sown in pots in the greenhouse. Plants were submitted to intermittent soil flooding each two days. After 60 days, the roots were sampled and analysis were done for the guaiacol peroxidase, ascorbate peroxidase, and catalase activities and for the capacity of the plants of each cycle to develop aerenchyma. The plants showed modifications in enzyme activity along the cycles, increasing the ascorbate peroxidase activity and decreasing the catalase and guaiacol peroxidase ones. A greater capacity to develop aerenchyma was also observed in the last selection cycles. Reductions in the enzyme activity of the antioxidant system seem to be related to a disorder in the H2O2 decomposition capacity