Rhizobium – legume relationship
Nitrogen forms eighty percent of the air in the atmosphere, which is necessary because all existing plants use nitrogen to survive. However, in some plants, conversion of nitrogen to a form that the plant can consume takes place. The conversion happens with the help of a unique species of bacteria in nature that have the enzyme nitrogenase. This enzyme is specialized in transforming atmospheric nitrogen into a form usable by plants (Suzaki et al., 124). These bacteria are known as nitrogen-fixing bacteria. The nitrogen-fixing bacteria are either free-living or live in a symbiotic relationship with certain plants. One community of nitrogen fixing bacteria, rhizobia, has evolved to establish symbiotic relationships with many plants of the legume family (Oldroyd & Giles 251). This paper is a discussion of the symbiotic relationship that exists between legumes and plants. The relationship is mutual in that the legume gets support from the plant due to the weak stem. On the other hand, the plant draws nitrogen from the legume plant.
The objective of this paper is to establish the relationship between the rhizobium and legumes. Secondly, the research work will bring out the benefits derived from the symbiotic relationship. Thirdly, the paper will bring out the unique nature of rhizobia and investigate the variety of rhizobia that exist. Rhizobia are very diverse in nature in that different legumes in varying locations on Earth contain their particular species of Rhizobia bacteria (Oldroyd and Giles, 253). However, the general mechanism by which each species processes nitrogen gas is similar.
Research shows that rhizobia are tolerant to soil stress effects brought about by alkalinity, acidity, and salt stress. This natural soil component is more efficient than merely adding nitrogen fertilizers to the soil. Previous research has been carried out to understand the morphology of nodules and their structure (Ardley et al., 12-15). Other studies focus on the rhizobium-legume interaction and seek to bring out the benefits and even the disadvantages of the relationship (Sachs et al., 1-2). The relationship between the bacteria and a given plant is highly specific. This is due to the secretion of flavonoid compounds by the legume that initiates the relationship. The secretions are attached to the bacterial gene known as nodD. The gene in the bacteria in turn activates plant nodD genes that are responsible for nodule formation (Liao et al., 3226). These nodules are factories for atmospheric nitrogen fixation. In the current experiment, the relationship between Rhizobium and two plants: clover and radish was studied. The growth of both radish and clover in presence and absence of Rhizobium was measured in terms of plant root and shoot length.
Consequently, this paper is a follow up on current and previous research studies that aim at understanding the legume-rhizobium relationship. The study seeks to justify the relationship and picks out some defects this symbiotic relationship causes in the ecology. Ultimately, the benefits are more than the disadvantages. The focus of this paper, however, is on the benefits of the interaction of the two plants. The hypothesis is that leguminous plants are dependent on the rhizobia for healthy growth. Lack of nitrogen in the soil leads to soil alkalinity.
Ardley, Julie K. et al. “Nodule Morphology, Symbiotic Specificity and Association with Unusual Rhizobia Are Distinguishing Features of the Genus Listia within the Southern African Crotalarioid Clade Lotononis S.l.” Annals of Botany 112 (2013): 1–15.
Sachs, Joel L et al. “The Legume- Rhizobium Symbiosis.” (2010): 1–18. Print.
Suzaki, Takuya, Emiko Yoro, and Masayoshi Kawaguchi. “Leguminous Plants: Inventors of the Root Nodules to Accommodate Symbiotic Bacteria.” International Review of Cell and Molecular Biology (2015): 124-234
Oldroyd, Giles ED. “Speak, friend and enter: signalling system that promotes beneficial symbiotic associations in plants.” Nature Reviews Microbiology 11.4 (2013): 242-263.
Liao, Chengsong, Frank Hochholdinger, and Chunjian Li. “Comparative analyses of 3 legume species reveals conserved and unique root extracellular proteins.” Proteomics 12.21 (2012): 3219-3228.