3-D reconstruction of soybean nodules provides an update on vascular structure

Authors: Livingston, David; Tuong, Tan; NOGUIERA, MARCO - Embrapa; Sinclair, Thomas

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2018
Publication Date: 1/7/2019
Citation: Livingston, D.P., Tuong, T.D., Noguiera, M., Sinclair, T.R. 2019. 3-D reconstruction of soybean nodules provides an update on vascular structure. American Journal of Botany. 106:507-513.

Interpretive Summary: Soybean nodules are located on roots and are the result of a symbiotic relationship between rhizobium bacteria and the plant. The nodules have the ability to fix atmospheric nitrogen into a form the plant can use for growth and thus are a very important aspect of soybean agronomy and crops that are planted after soybean. Much of the understanding of how nodules interact with the plant have been based on a two dimensional microscopic analysis. In this paper we used a three dimensional analysis developed in our laboratory to better understand the anatomy of water and nutrient conducting vessels in the soybean nodule and their connection to the root. Using this new analysis we found that contrary to existing 2-D observations the conducting vessels are organized in a continuous configuration around the nodule and they routinely have a dual connection to the root. These new findings mean that the nodule has a more robust and possibly more complex interaction with the soybean host plant.

Technical Abstract: Two-dimensional anatomical observations of soybean nodules have led to the assumption that the vascular bundles terminate within the cortex of the nodule and that a single vascular bundle connects the nodule to the root. However, when nodules of two soybean genotypes were sectioned and reconstructed in three dimensions it was found that vascular bundles did not always terminate within the cortex. In many cases, vascular bundles were found to have a continuous connection around the nodule. Also, 3-D reconstruction revealed a dual vascular connection between the nodule in 22 of the 24 nodules observed; of the 22 dual connections, 11 maintained two separate vascular bundles into the root with independent connections to the root vasculature. A more robust and possibly complicated pathway for vascular transport between nodules and soybean plants is indicated by these observations.