HERBICIDES

Paraquat, also called methyl viologen, is widely used by farmers as an herbicide (). Herbicides are known to control weeds by altering how they grow, by modifying the plants ability to make essential carbohydrates, lipids, and ultamatly preventing germination (if applyed before it turns into a seedling) (http://paraquat.com/knowledge-bank/crop-production-and-protection/mode-of-action-how-herbicides-work). Paraquat is used in a large variety of crops as it shows highly toxic effects to unwanted vegetation like weeds, grasses, and broad leaf plants (http://onlinelibrary.wiley.com/doi/10.1111/j.1399-3054.1982.tb04545.x/full). The purpose of this lab is to look at different effects of paraquat toxicity which causes changes in the lipid membrane bilayer of chlorosplasts (makes it leaky) and the formation of malondialdhyde in the bean Phaseolus vulgaris, by isolating the choloroplast, determining the chlorophyll concentration, determinating the protein amount by making a standard curve, and to exam the X-Ray diffraction. In addition, the purpose of this lab was also to gain experience in the lab by perfroming different techniques.
In plants, the paraquat acts in the presence of light (). This is because as the engergy of light is absrobed by chlorophyll (which is in the chloroplast) it is then moved via a flow of electrons through photosystem I (produces free electrons to drive photosynthesis) (). Paraquat is known to divert this flow, putting a halt to photosynthesis, as the paraquat ion reacts with the free electrons from photosynthsis I, to create the paraquat which is now in an oxidized form (paraquat radical formed) ().The paraquat cation radicle (a free radicle) then reacts with oxygen and creates a superoxide radical (O2-) (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC425696/). The superoxide radicle produced is highly reactive and as it attacks unsatturated membrane fatty acids, which quickly open up and disintergrate the cell membranes and tissues ().