Nodule Formation: Root Nodules are structures that are formed by the symbiotic relationship between leguminous plants and nitrogen-fixing bacteria. The root nodule formation is because of the need for obtaining nitrogen for the synthesis of amino acids, energy molecules – the phosphates such as ATP and assimilating in the nucleotides. And since the plants are themselves incapable of utilising atmospheric nitrogen directly they take the help of Rhizobia – general term for nitrogen-fixing bacteria and form the specialised structures known as root nodules.

Root Nodule Formation Steps

What are root nodules and how are they helpful, has been explained above. Let us proceed to understand how root nodule formation takes place. Given below are the root nodule formation steps:

• Root nodules function is to provide plants with an absorbable form of nitrogen. Thus, in absence of sufficient nitrogen, legumes release certain organic compounds called flavonoids which attract the Rhizobia towards the roots. 

• The Rhizobia reach to the tip of the root hairs and start to colonise the surrounding region. The flavonoids along with attracting the bacteria to the roots, also activate nod genes in the bacteria which leads to the release of the nod factors which initiate root nodule formation and the root nodule formation steps follow.

• The nod factors induce root-hair curling around the bacteria. The bacteria invade the root-hair and enter the root hair through a small tube opening known as the infection thread as it continues curling and following the infection thread the Rhizobia travel to the root cortex. 

• The bacterial cells when released from the infection thread into the root cortex, differentiate into rod-shaped specialised nitrogen-fixing cells called Bacteroides and are surrounded by the plant-derived symbiosome membrane. 

• The nodule thus formed, creates a vascular network with host plants for exchange of nutrients.

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By Team Learning Mantras