Question

While Rhizobium bacteria fix nitrogen in root nodules, what part of the plant produces new cells to form the nodules themselves?

Answer 1

The plant's cortical cells and pericycle cells, found in the root's vascular cylinder, divide and produce new cells to form the nodules.

Step-by-step explanation:

Cortical Cells and Pericycle Cells: The correct answer is that the cortical cells and pericycle cells in the plant's root vascular cylinder are responsible for producing new cells that form the nodules. These cells undergo division to initiate the nodule development.

Explanation in Detail:

Cortical Cells and Pericycle Cells: Within the root nodules, where nitrogen fixation occurs, the plant's cortical cells and pericycle cells play a crucial role. The cortical cells are part of the plant's cortex, the outer layer of cells in the root. The pericycle is a tissue layer in the vascular cylinder of the root.

Cell Division: The cortical cells and pericycle cells undergo cell division, leading to the formation of new cells. These newly formed cells contribute to the development of the nodules where Rhizobium bacteria establish a symbiotic relationship with the plant.

Nodule Formation: As these cells multiply, they create a suitable environment for the Rhizobium bacteria to colonize, leading to the formation of nodules. Within these nodules, nitrogen fixation takes place, converting atmospheric nitrogen into a form that the plant can use for its growth.

In summary, the plant's cortical cells and pericycle cells, specifically in the root's vascular cylinder, are responsible for generating new cells and facilitating the formation of nodules where nitrogen-fixing Rhizobium bacteria thrive.

Answer 2

While Rhizobium bacteria fix nitrogen in root nodules, the meristematic tissue in the root cortex produces new cells to form the nodules themselves.

Step-by-step explanation:

The process of symbiotic nitrogen fixation occurs in specialized structures called root nodules. These nodules are formed by a mutualistic relationship between leguminous plants and Rhizobium bacteria.

The Rhizobium bacteria, which are present in the soil, enter the plant's roots through small cracks or wounds. Inside the roots, the bacteria differentiate into bacteroids and fix atmospheric nitrogen into ammonia through an enzyme called nitrogenase. This ammonia is then used by the plant for various metabolic processes.

However, the formation of these nodules is not a passive process. The plant itself plays an active role in the formation of these structures. The initial steps of nodule formation begin with the perception of flavonoids, which are plant-derived compounds, by the Rhizobium bacteria. This perception triggers a cascade of molecular events that lead to the production of lipochitooligosaccharides (LCOs) by the bacteria. These LCOs act as signals for the plant to initiate nodule formation.

The meristematic tissue present in the root cortex is responsible for producing new cells that form these nodules. This tissue is characterized by its ability to divide continuously and produce new cells throughout the life of the plant. In response to LCO signals, this tissue begins to divide rapidly and differentiate into various cell types that form the nodule structure.

The initial cells that differentiate are called infection threads, which provide a pathway for bacterial entry into the plant's cells. As the infection threads grow, they differentiate into bacteroids, which are specialized bacterial cells that fix nitrogen within the nodule.

In summary, while Rhizobium bacteria fix nitrogen in root nodules, it is the meristematic tissue in the root cortex that produces new cells to form these structures themselves.

This process is initiated by molecular signals produced by both the plant and bacteria and involves a complex interplay between these two organisms. Understanding this symbiotic relationship can have important implications for agricultural practices as it provides a sustainable source of fixed nitrogen for leguminous crops without relying on synthetic fertilizers.