What plants does have root nodule?
they have got a root nodule
The rhizobium and soybean have a symbiotic relationship in which the rhizobium's root nodule is full of bacteria that helps convert the nitrogen from the air into an assimilable nutrient for the soybean, and in turn the rhizobium feeds from the sugar and nutrients that circulate in the soybean's roots. All plants in the legume family such as soybean, pea, alfalfa have such a nitrogen fixation role in crop rotations thanks to the rhizobium.
The root tip is provided with some specialized cells forming the root cap. The root cap protect the tender parts of the root as it makes its way through the soil. The root cap is ,however, absent in aquatic plants. In plants growing on rocks, the root tip secrets some acidic substance to facilitate the passage of the root.