What is it about?

Agriculture soils are becoming highly compacted due to shift in tillage practices which employs modern heavy machineries such as tractors and harvesters. Deeper soil profiles are likewise severely compacted therefore, roots find it challenging to penetrate through these hard layers of soils. The consequences of this soil compaction are significant: because it limits root growth while negatively affecting water and nutrient absorption from soils, besides affecting physical, biological, and chemical structure of the living soil. Employing X-ray imaging of plants growing in soil at Nottingham revealed that roots which remained narrow penetrate hard soils more easily. We have identified a stress signal (called ABA) that promoted this root swelling response which, when its levels were reduced, helped roots remain narrow and penetrate hard soil more effectively.

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Why is it important?

Compacted soils cause restricted diffusion of ethylene, thereby inhibiting the root elongation and swelling of root tips.We have discovered that ethylene controls these compaction responses via two distinct plant signals: Auxin and Abscisic Acid (ABA). Auxin is a hormone that inhibits root cell elongation in compacted soil, whereas ABA promotes the swelling of the root tips. Using mutants of rice ABA biosynthetic genes and computed tomography imaging at Nottingham University, we showed that plants lacking ABA had less swelling response in compacted soil, resulting in enhanced root penetration. As a result, we discovered that it was not the hard soil's resistance that limited plant root penetration but rather an increase in auxin and ABA levels caused by ethylene buildup within the root tips. This ethylene accumulation increased the amount of ABA, causing the root tip to swell and reduce its ability to penetrate compacted soil.

Perspectives

Our research overturns decades of scientific thinking, revealing that root swelling does not help penetrate hard soils. These results can potentially safeguard or boost agricultural yields worldwide, particularly considering that climate change can exacerbate the strength of soil by less rainfall. This new understanding of how roots grow in hard soils promises to help develop novel soil-compaction-resistant crops.

Bipin Pandey
University of Nottingham

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This page is a summary of: Ethylene inhibits rice root elongation in compacted soil via ABA- and auxin-mediated mechanisms, Proceedings of the National Academy of Sciences, July 2022, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2201072119.
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