Скачать или смотреть Medicago and Rhizobium - Root Nodule formation in Barrel Clover

In this series of time-lapse movies we are zooming in on the root nodule formation of Barrel Clover (Medicago truncatula). This type of endosymbioses between the plant and Rhizobia bacteria is typical for legumes and plays a very important role in a healthy soil. Bacteria of the genus Rhizobium are capable of nitrogen fixing. The bacteria fix atmospheric nitrogen into ammonium. In a sense making fertiliser out of thin air.

The plant secretes chemical signals (flavonoids) to attract rhizobia. The bacteria respond by producing a response signal (LCO (lipo-chitooligosaccharide) aka nodulation (Nod) factor). Upon perception of this return signal root nodules are initiated. This only occurs near the tip of the root. Region where root hairs are present. The susceptible zone. These hairs are needed for the infection. Medicago truncatula nodules are so called indeterminant nodules. Which means they keep on growing.

Inside the root nodules the Rhizobia bacteria will perform nitrogenase: Nitrogen fixing. Highly energy demanding, bacteria do this in return for energy from the plant. Bacteria have a protein complex called nitrogenase, responsible to produce ammonium. This complex is unstable and easily damaged by O2. The pink colour you see in the nodules is leghaemoglobin (the plants equivalent of what is in our blood). Leghaemoglobin binds O2 but can release it when needed. This ensures the conditions for nitrogenase and the cell to survive together.

The time-lapese were shot over a period of many months. The speed varies between 24 hours in one second for the roots and 24 hours in 4 seconds for the above ground shots.

Rhizobium bacteria and Medicago plants were provided by Wouter Kohlen (Plant Developmental Biology, Wageningen University)
https://www.wur.nl/en/research-result...

part of the Soil in Action Project in collaboration with Gerlinde De Deyn
https://research.wur.nl/en/persons/ge...

This video is part of the Soil Life in Action project. The movie can be used for education in classrooms and for lectures. For other use please contact: egmond(at)tip.nl

© Wim van Egmond 2023

visit Wim at https://www.wimvanegmond.com/