Experiment 15 - Symbiotic Nitrogen-Fixing Bacteria

What do most leguminous plants have on their roots?

Nodules or tumor-like-growths

How do the nodules form?

From a result of an infection of the root hairs

What bacteria causes root infection?

Rhizobium

What do the Rhizobium cells obtain?

• Energy for growth from host

• Grow to large populations within the nodule

What occurs during the growth?

The bacteria fix nitrogen gas (from air) and convert it to a “fixed” form of nitrogen which becomes available to the plant

What kind of relationship do plants and Rhizobium bacteria have?

A symbiotic relationship

What happens t the plant when the Rhizobium infects the root hairs?

The plant forms a membrane which invaginates inward extending into the secondary root

What is the purpose of invaginating inward into the secondary root?

Provides a passage for the bacteria and conducts them to the appropriate site for nodule formation

What is the nodular growth formed of?

Thin-walled parenchyma cells w Rhizobium bacteria

What does a nodule form on the plant?

A large swelling on the root

How do the plants benefit from the nodules?

Use the nitrogenous products synthesized by the bacteria