Chapter 20: MOA Part 5 – Seedling Root Growth Inhibitors

20.3 Herbicides that Interfere with Seedling Root Growth

There is one Herbicide Mode of Action group that hinders a plant’s ability to make spindle fibers:

  • Seedling Root Growth Inhibitors
    • Group 3. Microtubule Assembly Inhibitors (MAI) (HRAC Group K1)
diagram of cellular structures and where herbicide mode of actions impact plant cells
Figure 2. Cellular targets of herbicide action and herbicide classification by mode of action according to the Herbicide Resistance Action Committee (HRAC). Herbicides target only a few proteins or processes among the tremendous range present in plants. From: Deciphering the evolution of herbicide resistance in weeds. Christophe Delye et. al. 2013, Trends in Genetics. http://weedscience.com/summary/SOADescription.aspx

 

 

take action herbicide classification chart portion featuring seedling growth inhibitors
Figure 3 Excerpt from the Take Action Herbicide Classification Chart featuring Seedling Root Growth Inhibitors

Let’s now explore how these Group 3 Seedling Root Growth Inhibitors, ultimately interfere with plant growth.

There is a protein called tubulin that is part of the microtubules and spindle fibers.  It is the tubulin protein that this class of herbicides target.  Without that protein, spindle fibers can’t form.  Click through this animation to see how mitosis works normally and how it is disrupted from these herbicides.

 

cell diagram from animation featuring microtubules
Figure 4. Animation screenshot. Click the image above or the link below to visit the animation. The animation requires Flash player.

Visit the animation here: http://passel.unl.edu/pages/animation.php?a=spindle_fiber_inhibition.swf&b=997739817

The diagram below  also depicts the effects on chromosomes when spindle fibers do not form.  The results are disrupted cell division, cells with too many cells (polyploidy) and cell wall material that forms irregularly.  The effects on the plant seen include malformed roots, which present overall plant symptoms similar to drought and nutrient deficiencies.

group A shows the normal sequence of mitosis in a cell group B shows a shortened sequence of cell division terminating at mitosis
Figure 5 (A) Normal mitotic sequence and (B) effect of dinitroanaline herbicide on mitotic sequence in root cells. (Courtesy of F.D. Hess, Novartis Crop Protection, Inc)

Review and Reflection

Group 3 – Microtubule Inhibitors

Review and Reflection

 

License

Principles of Weed Control Copyright © by Deana Namuth-Covert and Amy Kohmetscher. All Rights Reserved.