Impact of exogenous alpha tocopherol on peanut seedlings (Arachis hypogaea L.) treated by norflurazon

Norflurazon 100 µM alone or in combination with α-tocopherol (0.25 mM) was applied in pre-emergence of peanut seedlings (Arachis hypogaea L.). Norflurazon treatment allowed to partially or totally photobleach plants which were noticeably smaller than the control. Norflurazon impaired the photosynthetic activity by decreasing photosynthetic pigments (carotenoids and chlorophylls) and by reducing quantities of soluble sugar. The determination of malondialdehyde (MDA) showed that its content was higher in treated plants in relation with enhancement of reactive oxygen species by the herbicide and decreased the endogenous α-tocopherol. The addition of exogenous α-tocopherol reduced the damage done by the herbicide at the membrane level because of the MDA content was less important than in norflurazon treated seedlings. Furthermore, the norflurazon decreased the glutathione S-transferase (GST) activity in the leaves and the roots of peanut seedlings, while it increased the level of reduced glutathione. This activity decreased even more with the application of exogenous α-tocopherol in combination with the herbicide. The herbicide alone or in association with the antioxidant α-tocopherol increased ascorbic acid content. The supplementation of α-tocopherol did not decrease the phytotoxicity of norflurazon although we observed a decrease in MDA content

Dégradation du Xyloglucane par les souches de Paenibacillus polymyxa isolées de la rhizosphère du blé dur sur des sols Algériens

Les espèces du genre Paenibacillus secrètent une variété d’enzymes extracellulaires parmi lesquelles figurent plusieurs types de β glucanases. Nous avons réalisé un test de dégradation du xyloglucane sur 29 souches isolées par immunopiégeage et identifiées à P. polymyxa par le système API50CHB. Ces souches ont été groupées en séries qui correspondent aux échantillons de sols à partir desquels elles avaient été isolées. Des souches de références et des souches type E. coli ont été intégrées lors de cette étude pour comparer leur activité à celles des souches isolées des sols d’Algérie. Les résultats de cette recherche montrent que toutes les souches de P. polymyxa sont capables de dégrader le xyloglucane, alors que les souches des espèces testées n’ont pas cette activité. Ces résultats semblent suggérer que cette propriété est partagée par tous les P. polymyxa et qu’elle n’est pas liée au sol d’origine de nos souches ni à l’ancienneté de culture du blé de ces sols. Nous avons également montré que la xyloglucanase fait partie du pool d’enzymes inductibles qui ne sont normalement présentes qu’à l’état de traces dans les bactéries, et dont la synthèse est amplifiée considérablement en présence de leur substrat

Assessment of SUNY Version 3 Global Horizontal and Direct Normal Solar Irradiance in Canada

AbstractIn this paper, hourly, daily and annual solar resource data derived form the latest SUNY solar model (version 3) using visible and infrared satellite data is analysed and compared with ground measured solar data from eighteen northern- latitude locations distributed all across Canada. The statistics of spatial and temporal differences between the two datasets obtained from the two versions of SUNY model, i.e., V1 and V3, are analysed for both global horizontal irradiance (GHI) and direct normal irradiance (DNI). SUNY V3 GHI and DNI data set is also compared to a dataset produced by the MAC3 cloud layer model for ten northern-latitude locations across Canada. The MAC3 model, using ground-based data, is the basis of the weather design input data files referred to in the current Canadian Model National Energy Code. It is also the model used for generating the CWEEDS (Canadian Weather Energy and Engineering Data Sets) long term hourly dataset, which is in turn used to derive the CWEC files (Canadian Weather year for Energy Calculations) also called typical meteorological years. CWEC files are used for design and analysis in various applications, including buildings heating and cooling as well as solar systems. Overall, results show that SUNY V3 has improved slightly compared to SUNY V1 in terms of estimating global and beam irradiance. Comparison of the SUNY V3 beta model with the MAC3 model seems to indicate that SUNY V3 model is resulting in better DNI estimates than those derived by the MAC3 model. Both SUNY V3 and MAC 3 models give similar estimates for GHI

Biochar and compost effects on the remediative capacities of Oxalis pes-caprae L. growing on mining technosol polluted by Pb and As

International audienceSelection of plant species with a great remediating capacity and a high biomass production is an important step for depolluting soils especially mine soils. Hyperaccumulators are used in phytoextraction for extracting metals from soil to roots and to translocate them to aerial parts. While in phytostabilization that usually requires amendment, metals are accumulated in the plant roots. The purpose of this study is to investigate Oxalis pes-caprae L. tolerance to Pb and As from Pontgibaud mine soil in France amended with compost and/or biochar. Oxalis bulbils were harvested in three sites located around Algiers: (1) an agricultural land in Reghaia, (2) an area planted with Pines at the USTHB university campus, and (3) the polluted bank of the El Harrach river. The small and medium bulbil sizes were selected from each locality. Concerning the experimental soil, five mixtures of Pontgibaud technosol (P) with amendments compost (C) and biochar (Bc) were prepared: PC, PBc5, PBc10, PBc5 C, PBcC (w/w). The results indicate that amendments alter the soil physico-chemical characteristics and the mobility of metal(loid)s. They also reveal that As and Pb are differently distributed in plant organs. Medium bulbils especially from El Harrach river and the university campus have shown a better growth. Seedlings growth rate has been the highest in Pontgibaud amended with PC and the lowest in PBc10

Variation in relative water content, proline accumulation and stress gene expression in two cowpea landraces under drought

International audienceMany landraces of cowpea [Vigna unguiculata (L.) Walp.] are adapted to particular geographical and climatic conditions. Here we describe two landraces grown respectively in arid and temperate areas of Algeria and assess their physiological and molecular responses to drought stress. As expected, when deprived of water cowpea plants lose water over time with a gradual reduction in transpiration rate. The landraces differed in their relative water content (RWC) and whole plant transpiration rate. The landrace from Menia, an arid area, retained more water in adult leaves. Both landraces responded to drought stress at the molecular level by increasing expression of stress-related genes in aerial parts, including proline metabolism genes. Expression of gene(s) encoding proline synthesis enzyme P5CS was up regulated and gene expression of ProDH, a proline catabolism enzyme, was down regulated. Relatively low amounts of proline accumulated in adult leaves with slight differences between the two landraces. During drought stress the most apical part of plants stayed relatively turgid with a high RWC compared to distal parts that wilted. Expression of key stress genes was higher and more proline accumulated at the apex than in distal leaves indicating that cowpea has a non-uniform stress response at the whole plant level. Our study reveals a developmental control of water stress through preferential proline accumulation in the upper tier of the cowpea plant. We also conclude that cowpea landraces display physiological adaptations to water stress suited to the arid and temperate climates in which they are cultivated

Interactions between photosynthesis and respiration during elicitor-induced cell death in tobacco

International audienceLight and oxygen are considered to be important in the execution of programmed cell death (PCD) in plants, principally because they are involved in the generation of reactive oxygen species (ROS). We compared the hypersensitive response (HR)-like PCD process in N. sylvestris leaves that is elicited by harpin Nea,, under light/dark and atmospheric/very low oxygen (VL ox: < 0,1%). PCD was induced under all conditions, but it was delayed in the dark and accelerated under VL ox. Rapid inhibition of photosynthesis and an acceleration of respiration are characteristic of light–elicited leaves. The harpin-induced collapse of CO2 assimilation and photosystem II activity was delayed under VL. Moreover, the burst of CO2 release caused by enhanced mitochondrial respiration in dark-elicited leaves was inhibited under VL ox. Superoxide and hydrogen peroxide accumulation inside the chloroplasts was observed in both the light and the dark, but not under VL ox. The accumulation of transcripts encoding cytosolic antioxidant genes was also greatly affected by oxygen deprivation. These results indicate that extra-mitochondrial ROS are not key signals to harpin-induced cell death. Rather, the acceleration of the HR-like process under VL ox is associated with the perturbation of respiratory pathways and possibly enhanced mitochondrial ROS production

Light and oxygen are not required for harpin-induced cell death

Nicotiana sylvestris leaves challenged by the bacterial elicitor harpin NEa were used as a model system in which to determine the respective roles of light, oxygen, photosynthesis, and respiration in the programmed cell death response in plants. The appearance of cell death markers, such as membrane damage, nuclear fragmentation, and induction of the stress-responsive element Tnt1, was observed in all conditions. However, the cell death process was delayed in the dark compared with the light, despite a similar accumulation of superoxide and hydrogen peroxide in the chloroplasts. In contrast, harpin-induced cell death was accelerated under very low oxygen (<0.1% O2) compared with air. Oxygen deprivation impaired accumulation of chloroplastic reactive oxygen species (ROS) and the induction of cytosolic antioxidant genes in both the light and the dark. It also attenuates the collapse of photosynthetic capacity and the respiratory burst driven by mitochondrial alternative oxidase activity observed in air. Since alternative oxidase is known to limit overreduction of the respiratory chain, these results strongly suggest that mitochondrial ROS accumulate in leaves elicited under low oxygen. We conclude that the harpin-induced cell death does not require ROS accumulation in the apoplast or in the chloroplasts but that mitochondrial ROS could be important in the orchestration of the cell suicide program