How plants grow under the ground
An intercontinental team of 30 researchers composed of mathematicians, engineers, computer scientists and plant sciences researchers has developed new explanations about how root plants grow and develop. As roots provide the crops we eat with water and nutrients, it is essential to learn how they grow -- laterally. 'Lateral roots, as their name suggests, extend horizontally from the primal root, otherwise referred to as parent root, helping the plant to anchor itself in the soil.' This lateral growth, which improves plant stability from violent winds, is achieved with the help of the plant hormone auxin (from the greek word auxano, to grow). But read more...
You can see above several pictures describing this lateral root plant development. (Credit: Malcolm Bennett and 30 other researchers) Here is the original -- but somewhat difficult to interpret -- caption. "LAX3 expression is induced outside the developing lateral root primordia LAX3pro:GUS expression is illustrated at every stage of lateral root primordia development (denoted by roman numerals)."
This research work involved -- at least -- 31 scientists from various laboratories in Europe, Asia and the U.S. It was led by Malcolm Bennett, Professor of Plant Sciences, and other researchers in his lab and at the Centre for Plant Integrative Biology (CPIB), which is part of the Division of Plant and Crop Sciences at the University of Nottingham, UK. For more information about Bennett's research, take a look at these pages about Root Developmental Biology and Root Systems Biology.
But let's come back to the EUROPA news release to discover the importance of lateral roots. "Lateral roots, as their name suggests, extend horizontally from the primal root, otherwise referred to as parent root, helping the plant to anchor itself in the soil. Their first mission is to pass through several layers of tissue before they can enter the soil. Once they have entered the soil they then branch out sideways looking for nutrients and water to help the plant sustain itself. As they extend through the soil, the roots show a wide variation in the way they grow through the soil to exploit the available resources. Olive trees for example, have been known to extend their roots laterally several meters out from their trunk. Without the roots offering stability and providing nutrients, the plant would die."
So how lateral roots grow? "Lateral root growth is achieved when the plant hormone auxin (from the greek word auxano, to grow) acts as a local inductive signal which re-programmes adjacent cells. Auxin then induces the expression of LAX3, which in turn promotes the induction of cell-wall-remodelling enzymes. This results in increased cell separation, allowing the lateral roots to move out."
Here is one Bennett's comment about this discovery. "In addition to providing new biological insight into lateral root emergence, we have identified a large number of genes that control this process. This is really important because this may enable us to breed crops with improved root architecture in the future."
For additional details, here are some excerpts from a previous Nottingham University news release, "The emerging story of plant roots" (July 15, 2008). "Although less visible than shoots, leaves and flowers, plant roots are critical to our lives. They provide the crops we eat with water, nutrients, a firm anchor and a place to store food. Roots are complex branching organs and show a wide variation in the way they grow through the soil to exploit the available resources. The way that new lateral roots are formed and grow is key to this process. Lateral roots originate deep within the parent root and must emerge through intervening layers of tissues before entering the soil. Despite its importance to the integrity and architecture of the root system, little is known about the regulation of lateral root emergence. This question has fascinated, yet frustrated, scientists since the nineteenth century."
Now, they got some answers, and their research work has been published in Nature Cell Biology under the title "The auxin influx carrier LAX3 promotes lateral root emergence" (Volume 10, Issue 8, Pages 946-954, August 2008). Here is the text of the abstract. "Lateral roots originate deep within the parental root from a small number of founder cells at the periphery of vascular tissues and must emerge through intervening layers of tissues. We describe how the hormone auxin, which originates from the developing lateral root, acts as a local inductive signal which re-programmes adjacent cells. Auxin induces the expression of a previously uncharacterized auxin influx carrier LAX3 in cortical and epidermal cells directly overlaying new primordia. Increased LAX3 activity reinforces the auxin-dependent induction of a selection of cell-wall-remodelling enzymes, which are likely to promote cell separation in advance of developing lateral root primordia."
If you want to learn more about this growth process, here is a link to the full article (PDF format, 9 pages, 2.58 MB). The above illustration has been extracted from some supplementary information to this article (PDF format, 6 pages, 1.60 MB).
Sources: European Research Headlines, August 27, 2008; and various websites
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