Nodule formation on the roots of leguminous plants has been well analyzed morphologically. Based on these analyses, root nodule formation has been divided into 3 distinct steps; (i) the pre-infection stage, (ii) infection and nodule formation, and (iii) nodule function and maintenance. During the pre-infection stage (brady)rhizobia interact with growing root hairs and induce root hair curling. During the second stage, the bacteria invade the root hair cell and the root cortex through the infection thread. Meanwhile, but independently from the infection process, cortical cells start dividing at several places and at these sites, the nodule primordia are formed. Infection threads grow towards these primordia and upon contact rhizobia are released from the tips of the infection threads into the cytoplasm of the plant cells. During the third stage, the bacteria differentiate into pleomorphic bacteroids that fix atmosphere nitrogen.
KeywordsRoot Hair Nodule Development Infection Thread Grow Root Hair Indeterminate Nodule
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