Hayet Houmani

Alleviation of Cr(VI)-induced oxidative stress in maize (Zea mays L.) seedlings by NO and H2S donors through differential organ-dependent regulation of ROS and NADPH-recycling metabolisms

Chromium (Cr) contamination in soil is a growing concern in relation to sustainable agricultural production and food safety. Nitric oxide (NO) and, more recently, hydrogen sulfide (H2S) are considered to be new signalling molecules with biotechnological applications in the agronomical sector. Using 9-day-old maize (Zea mays) seedlings exposed to 200μM Cr(VI), the potential mitigating effects of exogenous NO and H2S on chromium-induced stress in maize seedlings were investigated in roots, cotyledons and coleoptiles. Analysis of Cr content, lipid peroxidation, antioxidant enzymes (catalase and superoxide dismutase isozymes), peroxisomal H2O2-producing glycolate oxidase and the main NADPH-regenerating system revealed that chromium causes oxidative stress, leading to a general increase in these activities in coleptiles and roots, with the latter organ being the most affected. However, cotyledons behaved in an opposite manner. Moreover, exogenous applications of NO and H2S to Cr-stressed maize seedlings triggered a significant response, involving the virtual restoration of the values for all these activities to those observed in unstressed seedlings, although their specific impact on ROS and NADPH-recycling metabolisms depends on the seedling organ involved. Taken together, the data indicate that gas transmitters, NO and H2S, which act as a defence against the negative effects of hexavalent chromium contamination, are alternative compounds with potential biotechnological applications.

Glyphosate-induced oxidative stress in Arabidopsis thaliana affecting peroxisomal metabolism and triggers activity in the oxidative phase of the pentose phosphate pathway (OxPPP) involved in NADPH generation

Glyphosate is a broad-spectrum systemic herbicide used worldwide. In susceptible plants, glyphosate affects the shikimate pathway and reduces aromatic amino acid synthesis. Using Arabidopsis seedlings grown in the presence of 20μM glyphosate, we analyzed H2O2, ascorbate, glutathione (GSH) and protein oxidation content as well as antioxidant catalase, superoxide dismutase (SOD) and ascorbate-glutathione cycle enzyme activity. We also examined the principal NADPH-generating system components, including glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), NADP-malic enzyme (NADP-ME) and NADP-isocitrate dehydrogenase (NADP-ICDH). Glyphosate caused a drastic reduction in growth parameters and an increase in protein oxidation. The herbicide also resulted in an overall increase in GSH content, antioxidant enzyme activity (catalase and all enzymatic components of the ascorbate-glutathione cycle) in addition to the two oxidative phase enzymes, G6PDH and 6PGDH, in the pentose phosphate pathway involved in NADPH generation. In this study, we provide new evidence on the participation of G6PDH and 6PGDH in the response to oxidative stress induced by glyphosate in Arabidopsis, in which peroxisomal enzymes, such as catalase and glycolate oxidase, are positively affected. We suggest that the NADPH provided by the oxidative phase of the pentose phosphate pathway (OxPPP) should serve to maintain glutathione reductase (GR) activity, thus preserving and regenerating the intracellular GSH pool under glyphosate-induced stress. It is particularly remarkable that the 6PGDH activity was unaffected by pro-oxidant and nitrating molecules such as H202, nitric oxide or peroxynitrite.

Physiological Responses of Wild and Cultivated Barley to the Interactive Effect of Salinity and Iron Deficiency

Literature on the separate effects of salinity and inadequate Fe supply on plant growth and nutrient uptake, concentration, and distribution is abundant but little is known about the interactive effects of these two abiotic constraints. Here, we investigated the interactive effect of iron availability and salinity on physiological responses of cultivated and wild barley (Hordeum vulgare and H. maritimum resp.). Seedlings of both species were grown for 9 days, under complete nutrient solution with or without iron supply. Then, NaCl treatment was applied at different concentrations (0, 100, 200, and 300 mM) for 60 hours. After salt exposure, shoot water content of H. vulgare was significantly reduced as compared to H. maritimum. Furthermore, Na

Implication of Rhizosphere Acidification in Nutrient Uptake by Plants: Cases of Potassium (K), Phosphorus (P), and Iron (Fe)

The rhizosphere represents the interface between soil and roots. In this zone, many interactions between plant roots and the soil solution occur and result in important modifications of the physicochemical properties in this area. Plants require large amounts of nutrients to assure maximum growth and development. The absorption of excess nutrients by roots leads to many changes in the rhizosphere such as the acidification phenomenon which is known to be a continuous process in many soils through the world. It is due to the extrusion of protons at the root plasma membrane in favor of cation influx, a principal way used by plants to remove nutrients from the soil solution. Rhizosphere acidification plays a crucial role in nutrient acquisition by plants and is attributed to the activity of H+ATPase pumps located at the plasmalemma. The implication of proton release in nutrient acquisition by plants was proved under low nutrient availability. Thus, an increase of the H+ATPase activity was noted under a deficiency in many essential nutrients. Due to new advances in molecular biology, the role of H+ATPases in nutrient uptake by plants is more elucidated and many genes encoding these pumps are identified. In the present chapter, we summarize information gained on the role of rhizosphere acidification in the uptake of two essential macronutrients and a key micronutrient, respectively, potassium (K), phosphorus (P), and iron (Fe), especially under deficiency conditions and we describe the recent findings related to H+ATPases that drive the acidification process.