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Abstract It has long been known that certain ionic substances can be extremely detrimental to the basal metabolism of plant species, when they reach a high enough concentration. This phenomenon has severe consequences in areas of the third world, with vast tracts of land unsuitable for crop growth due to salinization from poor farming practice and drought. However, this detrimental effect varies greatly between ionic substance and plant species and the differential toxicity of the ions was not
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  Abstract It has long been known that certain ionic substances can be extremely detrimental to the basal metabolism of plant species, when they reach a high enough concentration. This phenomenon has severe consequences in areas of the third world, with vast tracts of land unsuitable for crop growth due to salinization from poor farming practice and drought. However, this detrimental effect varies greatly between ionic substance and plant species and the differential toxicity of the ions was not known. With this in mind, solutions containing different ions were made up and added to 5 samples of the species  Arabidopsis thaliana , and 5 samples of species Thellungiella halophila , and the effect was observed in terms of reduction of leaf matter mass over a period of time, then the difference in effect of each salt on each species was compared. Introduction Of all abiotic stress factors, soil salinity is one of the most detrimental to plant growth. It severely affects crop production in arid lands and is quickly becoming a great threat to sustainable agriculture. One main source of soil salinity arises from the practice of irrigation without first having proper drainage facilities. This leads to water evaporating off the surface of the soil and depositing salt  behind which then accumulates and results in the loss of valuable agricultural areas. The effect salinity has upon the growth of a plant varies depending on the type of ions, the concentrations and the species of plant involved. Salinity Stress in Plants Sodium chloride (NaCl), the most abundant salt found naturally and the most studied, causes damage to plants in two different ways, by osmotic stress and by ion toxicity. Osmotic stress is the disruption of the ordinary difference in osmotic pressure between the plant and its environment. Maintaining an osmotic pressure that is higher relative to the soil solution is crucial for plants in order to take up water and minerals through their roots. A high NaCl concentration in the soil increases the osmotic  pressure of the soil solution therefore hindering and sometimes even blocking the uptake of essential molecules like water or potassium ions. Ion toxicity arises when high levels of sodium and chlorine ions directly enter the plant, where they disrupt cell membranes and metabolic activity. Some enzymes are critically affected by the presence of high sodium ion concentrations and high Na ⁺ /K  ⁺  ratios in the cytosol. Sequential secondary damage then occurs in the plants as a consequence of these impacts. This is characterised by the immediate production of abscisic acid due to osmotic stress leading to closure of stomata which results in the abating of photosynthesis. Prolonged exposure to salt causes growth inhibition, accelerated development, senescence and then eventually cell death. Interestingly, research shows some of the stress can be lessened by the addition of calcium ions. Calcium works by conserving the transport of potassium and increases the effectiveness of ion pumps, allowing cells to better maintain low cytosolic Na ⁺  concentrations and low Na ⁺ /K  ⁺  ratios .  Arabidopsis and Thellungiella Arabidopsis, like most plants, is a glycophyte. This means it does not tolerate salt well and can only withstand NaCl concentrations of between 100-200 mM. However Thellungiella, a halophytic relative of Arabidopsis, is able to grow in salt concentrations of up to 500 mM. Halophytes have gained tolerance through a number of specific adaptations which allow them to cope with high salt environments. In halophytes, salt stress is accompanied by a large increase in cytosolic    , activating sodium pumps and increasing discrimination between potassium and sodium. Na ⁺  that accumulates in the cell is actively pumped into and stored in the vacuole to protect cytosolic enzymes from damage. Lastly, large amounts of benign compatible osmolytes are synthesised and allowed to  build-up in the cytosol to offset the increased osmotic pressure caused by extracellular and vacuolar ions. These are but a few examples of the methods plants use to deal with sodium chloride stress. Little is known about the relative toxicity of other salts on top of sodium chloride. In this report we will examine the effects of References http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2881266/ http://www.faculty.ucr.edu/~jkzhu/articles/2007/ELS%20Zhu.pdf  http://thellungiella.org/ http://tjeas.com/wp-content/uploads/2012/09/7-10ok.pdf  http://www.plantphysiol.org/content/147/3/1168.full  Methodology 25 Arabidopsis thaliana plants and 25 Thellungiella halophila plants were grown to maturity, and then starved of water for a week. The plants were split into 5 experiment groups containing 5 individuals of each species. 5 measurements of 5.84g of NaCl were dissolved in 5 separate flasks containing 500ml of distilled water, creating a 200mM solution of NaCl. 3.68g of CaCl2, 1.86g of KCl, 5.08g of MgCl2 and 3.56g of Na2SO4 were each dissolved in 50ml of distilled water then each solution was added to a different flask of 200mM NaCl. Each of the resulting solutions was then added to a different batch of the 2 plant species. EXPERIMENT NO. SALT SOLUTION ADDED 1 (control) 200mM NaCl in 500ml distilled H2O 2 200mM NaCl+ 50mM CaCl in 500ml distilled H2O 3 200mM NaCl+ 50mM KCl in 500ml distilled H2O 4 200mM NaCl+ 50mM MgCl2 in 500ml distilled H2O 5 200mM NaCl+ 50mM Na2SO4 in 500ml distilled H2O The experiment groups were then safely stored in a growth room for 1 week and starved of water once again. After this the experiments were taken out of the growth room, photographed to observe the morphological differences, then the ‘fresh weight’ of each plant was measured. In order to do this a weighing boat was place on a balance and the weight was set to ‘0’ by pressing ‘tare’. The entire plant was excised from the soil using a volunteer’s hands, and the root matter was clipped off using scissors, leaving only the leaf matter. The leaf matter of each was individually placed in the weighing boat; the weight was measured and noted. The leaf matter was then placed on aluminium foil, and the weighing boat was placed back on the scales and set to ‘0’. This process was repeated for each specimen, with each sample (group of five plants) placed in the same tin foil wrap which was carefully folded. Each wrap was the weighed on the weighing boat and the combined weight of the foil and plants was noted down. The ten samples were then labelled with the group and sample name, then placed in an oven to dry for one week. Figure 1- The 10 sample groups, shortly after removal from the growth room  After the samples had been in the oven for one week, they were taken out and the dry weight was measured. This was again done using a weighing boat and set of scales. The weighing boat was placed on the scales, set to ‘0’and then each sample was measured a nd the weight noted. The dry weight of each sample was then measured. The standard deviation and standard error were then calculated, and then noted down for each sample. The average water content of each individual was then calculated by subtracting the dry weight of each sample from the wet weight. The percentage of water content of the average individual was then calculated using the following formula:          After this, the results were collated, and placed in tables and graphs in order to be analysed more efficiently.
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