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THE EFFECTS OF RHIZOBIUM ON SOYBEAN GROWTH IN POOR AND RICH NITROGEN SOIL INTRODUCTION The meaning of this experiment was to test the three hypotheses when planted in a nitrogen poor soil soybeans will grow larger if their roots are infected with the nitrogen fixing bacteria Rhizobium Also if planted in a nitrogen rich soil soybeans will resist becoming infected by Rhizobium Lastly if planted in a nitrogen rich soil than soybeans that do become infected by Rhizobium will grow less than those that are not infected The most widespread of symbiotic relationships are those between the plant family Fabaceae and the bacterial genus Rhizobium Rhizobium bacteria enter roots through the root hairs The first nodules are formed on the primary root The invading bacterium induces the formation known as an infection thread The infection thread grows through the root hair cell and into the cells root cortex When the thread grows through the root cortex bacteria are released the bacteria are then enclosed by a portion of the plasma membrane surrounding the thread The root nodules then begin to form Root nodules are necessary for nitrogen fixation without them nitrogen fixation cannot occur During nodule development Rhizobium bacteria undergo morphological and physiological changes They change from their typical rod shape found in free living bacteria to twisted and branch shaped forms The bacteria in nodules are so unlike their free living relatives that they are termed Bacteroids The reduction of N2 to ammonium is catalyzed by the enzyme nitrogenase Nitrogenase requires anaerobic conditions to function properly This is accomplished by the protein leghemoglobin which has a high affinity for oxygen This allows the anaerobic conditions to be maintained while the roots can still receive a supply of oxygen The enzyme nitrogenase requires large amounts of energy to break the nitrogen bond This
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