A comparative light microscopic study of two types of root nodule bacteria dispersal into the bacteroid zone cells

Abstract

Root nodule bacterial dispersal into the cells and formation of bacteroid zone cells of root nodules have been observed in several species of Leguminosae. Two different types of bacterial dispersal were recognized comparable to those briefly mentioned by a few authors.

Cell division type: From the very beginning of nodule development there exist two different kinds of cell in the meristematic region. In bacteria-containing cells the bacteria are distributed into two new cells with host cell division, the bacteria being located outside the spindle region during mitosis. In those cells not containing bacteria, amyloplasts develop in the cytoplasm. These cells also divide mitotically, increasing the numbers of amyloplast-containing cells. These two different cell populations compose the bacteroid zone. This type was seen inSophora flavescens andCytisus scoparius.

Infection thread type: In the transitional zone from the nodule meristem to the bacteroid zone, some cells are penetrated by infection threads and others are not. Infected cells become bacteroid-filled cells, no mitosis taking place after penetration of the infection thread. Uninfected cells become amyloplast-containing cells, increasing their numbers by mitosis. These two cell populations compose the bacteroid zone. This type was seen inVicia sativa, V. faba, Trifolium repens andAstragalus sinicus.