One must also consider the potential for the formation of metabolites and the consequences of exposure to all non-target organisms in order to better understand the fate and risks of CECs in terrestrial environments. The results have potential implications for policy makers and other stakeholders attempting to assess the risks for the land application of treated wastewater and bio solids.The results presented in this dissertation suggest the highly chemical-, species-, and research technique- specific nature of the environmental fate of CECs. For example, cell cultures often form amino acid conjugates while whole plants form sugar conjugates during xenobiotic metabolism. The differences in CEC metabolism imposed by treatments or species warrant further investigation. Additionally, more toxicological data are needed on the effects of these and other compounds in terrestrial invertebrates, especially for those of agricultural importance. From the research conducted in this dissertation, future research should focus on the impacts of exposure and the potential for transformation of CECs under different conditions and in multiple species. Future studies should place emphasis on experimentation using bio solids and TWW with inherent compounds and field conditions to improve environmental relevance.
Future risk assessments should be conducted by taking into account the formation of biologically active and conjugated metabolites,arandano azul cultivo and with regard to the potential toxicity of CECs in non-target terrestrial organisms. Excessive soil salinity is an important constraint limiting the distribution of plants in natural habitats, and is an increasingly severe agricultural problem in arid and semi-arid regions . In Tunisia, the arid Mediterraneanan bio-climatic regions are frequently irrigated with water leached in salt. Consequently, about 10% of the whole territory area and 20% of the cultivated lands are salinized . Enhancing salt tolerance in plants has major implications in agriculture. Salicylic acid is now considered as a hormone-like endogenous regulator, and its role in the defence mechanisms against biotic and abiotic stressors has been well documented . SA has been suggested to be physiologically important in stress tolerance since exogenous SA brought about plants tolerance to various abiotic stress including drought and salt . The ameliorative effects of SA has been well documented in inducing salt tolerance when applied as a soil drench in bean and tomato, addition to hydroponic culture in tomato, and seed treatment in tomato and barley . The aim of this work was to study the responses of growth and mineral nutrition in tomato plants, cv Marmande to the interactive effects of salicylic acid 0.01 mM and NaCl treatment 100 mM. But this reduction was suppressed when adding SA 0.01mM to the culture medium.
Salicylic acid-treated tomato plants exhibited an increase in tolerance to salt treatment. In fact, exogenous applied SA increased dry weight of the 3 organs significantly both in saline and non-saline conditions. In saline conditions, with the applicatoin of SA , dry yield increased almost up to the yield obtained from the non-saline control treatment. We observed stimulation of about 38% compared to the control medium. The improvement of the tolerance to salt by SA can be related to two factors: the stimulation of the activity of growth of the roots and the attenuation of the depressive effect of NaCl on the shoots. Salinity decreased leaf area of tomato plants significantly . The reduction was about 80% at the 5 stage and 40% at the 3 stage. Exogenous applied SA increased leaf area significantly both in saline and non-saline conditions. At the 5 stage, we noted stimulation about 63% in the leaf area compared to the control medium. Salinity treatment significantly affected total chlorophyll contents . Whereas, the addition of SA in the culture medium induced a significant increase in this parameter . The stimulation was about 50% compared to the plants treated only by NaCl 100 mM. Tomato , one of the important and widespread crops in the world, is sensitive to moderate levels of salt in the soil. So many authors have reported large variation among tomato genotypes in their response to salinity. The salt concentrations we have used are within the range found in water used for irrigation purposes in regions with a Mediterranean climate . This salt concentration caused significant reductions in all growth parameters , so Marmande was considered as a sensitive variety to salt.
This reduction of growth does not relate to the roots, but is explained by the strong sensitivity to salt of the aerial parts. Similar results were found in the tomato varieties Marmande and Rio Grande . Salinity stress results in a clear stunting of plant growth, which results in a considerable decrease in the dry weights of leaves, stems and roots . The immediate response of salt stress is reduction in the rate of leaf surface expansion leading to cessation of expansion as salt concentrations increases . Our results showed a significant decrease in leaf area of tomato plants. The reduction was about 80% at the 5 stage and 40% at the 3 stage . Salinity stress also induced a reduction in total chlorophyll contents . The decreased in chlorophyll content under salinity stress is a commonly reported phenomenon in various studies, because of its adverse effects on membrane stability . The chlorophyll contents of leaves of different tomato cultivars decreased by NaCl stress . Under salinity stress, leaf pigments, studied in nine genotypes of rice, reduced in general . The development of methods and strategies to ameliorate deleterious effects of salt stress on plants has received considerable attention. Salicylic acid has been shown as an important signal molecule for modulating plant responses to environmental stress . Exogenous application of SA may influence a range of diverse processes in plants, including seed germination , ion uptake and transport , membrane permeability , and photosynthetic and growth rate . In addition to facilitating the growth of plant, SA has been shown to play a role in mitigating the deleterious effects of some environmental stresses including low temperature, salinity, and cadmium stress . Our results showed that exogenous application of SA through the rooting medium had an ameliorative as well as growth promoting effect under both non-saline and saline conditions . It was shown in a previous work that 0.5 mM of SA added in the hydroponics solution of maize increased its tolerance to salt stress . Dhaliwal et al. attributed this amelioration in growth production to an increase in photosynthesizing tissue of leaves. This was in agreement with our results. In fact, application of 0.01 mM SA through the rooting medium increased pigments chlorophyll in salt stressed plants . This effect of SA application on photosynthetic pigments was expected in many studies that showed increased or decreased photosynthetic pigments following SA application, depending on type of species . Greenway and Munns suggested that the susceptibility of many glycophytes to salt is due to an insufficient ion supply. Indeed, in tomato, salt reduces K+ supply and induces Ca2+ and Mg2+ deficiency . Salt has a depressive effect on the whole plant growth of Marmande. Tomato plants grown in the presence of NaCl accumulated large amounts of both Na+ and Cl- ions . In the other case, the presence of salt in root medium causes disturbances in the essential mineral nutrition of the plant. NaCl severely reduces K + , Ca2+, and Mg2+ uptake and translocation from roots to shoots . Consequently,macetas 25 litros selectivity in favour to potassium decrease with salinity . Whereas SA addition ameliorates this parameter. In fact, at salinity level 100 mM NaCl, the K/ ratio in leaves was equal to 0.38. Applied SA in the culture medium significantly decreased the Na+ and Cl- concentrations in saline conditions. Whereas K+ , Ca2+, and Mg2+ uptake increased with the addition of SA in saline medium.
Thus K/ ratio was enhanced when adding SA 0.01mM to the saline medium . Thus SA ameliorate the aptitude of whole plant to ensure a sufficient supply K + by maintaining a high selectivity for this essential nutriment, in spite of excess of Na+ in the medium. This result is in agreement with those of Gunes, et al. , who demonstrated that salicylic acid strongly inhibited Na and Cl accumulation, but stimulated N, Mg, Fe, Mn, and Cu concentration of stressed maize plants. According to these authors, the increase in dry matter content might be attributed to the increased mineral uptake by stressed plant with SA. Furthermore, it has been reported that SA applications increase carbon dioxide assimilation and photosynthetic rate, thus increasing dry matter . This improvement in growth yield might also be related to the effect of SA on membrane permeability. The cellular membrane dysfunction due to stress is well expressed in its increased permeability for ions and electrolytes which can be readily measured by the efflux of electrolytes . NaCl treatment induced significant increases in electrolyte leakage in tomato plants compared with the control . Similar results were obtained by Lutts et al. who reported that salinity increased the membrane permeability of sensitive rice varieties. Addition of salicylic acid in the culture medium decreases permeability of membrane in salt treated plants . This agrees with the findings of Stevens and Senaratna who demonstrated that SA application reduced electrolyte leakage by 44 and 32% in tomato plant growing respectively under 150 and 200 mM NaCl, compared to untreated plants. One important strategy of several species to tolerate salinity was to use NaCl as an osmoticum and to compartmentalize the Na+ and Cl- ions primarily in the leaf vacuoles. The appreciation of the capacity of plant to compartmentalize the Na+ in the leaf vacuoles was possible by correlating the water contents of the leaves with the Na+ contents of these organs . The data in Figure 5, correlating leaves water content with its Na+ content, showed that the presence of salt in the medium induce a sodium accumulation in the photosynthetic organs of tomato.As an essential macro-nutrient for plant growth and development, potassium nutrient status in soils has direct consequences on crop yield and quality . Since soluble K+ in most arable fields is low, crop production relies on extensive use of K+ fertilizers . However, heavy use of fertilizers is not sustainable because fertilizers are costly and cause environmental pollution . To support sustainable agriculture, a key strategy is to breed crops with improved K+ use efficiency so that they can produce more with less input of fertilizers, which requires a thorough understanding of molecular mechanisms that allow plants to respond and adapt to limited K+ availability in the soil. While cellular K+ concentration in plants is maintained at approximately 100 mM, the typical K+ concentration in natural soils fluctuates between 0.1 and 1 mM. After the uptake of K+ from the soil into the root symplast and subsequent release into the xylem apoplast, K+ is translocated from root to shoot and distributed throughout the plant. Once arrived in sink cells, K+ is utilized for cellular metabolism and osmoregulation with excess K+ sequestered into the vacuole. K+ efflux from plant cells is also involved in the adjustment of intracellular K+ homeostasis in response to altered environment conditions. To deal with K deficiency, plants have evolved two major mechanisms to maintain K+ homeostasis in plant cells, one is K+ acquisition from the soil and another is K+ remobilization from vacuolar stores. In Arabidopsis roots, the high-affinity K+ transporter HAK5 and the inward-rectifier K+ channel AKT1 are two major contributors to K+ uptake under K-limiting conditions in the natural soil. The vacuolar K+ -pool is stocked up in times of sufficiency, but under K+ limited environments, several tonoplast K+ -permeable channels, including two-pore K+ channels, facilitate K+ remobilization from the vacuole to support a stable concentration in the cytoplasm. An interesting question arises: how does a plant cell balance the demand and supply of K+ by connecting K+ status with the activity of channels and transporters ? This question has been addressed by studies on a calcium-dependent signaling mechanism consisting of calcineurin B-like calcium sensors and CBL-interacting kinases . A typical CBL-CIPK signaling module is activated by elevation in free cytosolic Ca2+ that binds to CBLs through their EF hand motifs and trigger conformational changes. Activated CBLs interact with CIPKs that transphosphorylate and modulate the activity of downstream targets such as ion transporters. In the case of low-K+ response, K+ deficiency has been shown to triggers distinct Ca2+ changes in Arabidopsis roots, which may activate CBL-CIPK signaling pathways that in turn promote K+ -uptake and/or vacuolar remobilization.