What do frog eggs have in common with anti-aging creams? Their success depends on a group of chemical compounds called retinoids, which are capable of generating and re-generating tissues.
A new study in plants shows that retinoids' tissue-generating capacities are also responsible for the appropriate development of roots.
If you've ever planted a radish seed, you know that the first thing it does is develop a long vertical root. Give it a bit more time, and it will get smaller roots that run perpendicular to the plant's stem. Over time, these lateral roots will branch repeatedly and spread out, forming a web that stabilizes and feeds the plant.
These lateral roots don't just spring out randomly. They appear and then branch out at regular intervals along a main axis, following a rhythm. What regulates and determines their development and rhythm was not known, until now.
In a new study, appearing August 26 in the journal Science, a research team led by Alexandra Dickinson, assistant professor at the University of California, San Diego, and Philip Benfey, the Paul Kramer Distinguished Professor of Biology at Duke University, identifies the compound that plays a key role in triggering the development of plants' lateral roots.
The research team had a good suspect: retinal, a type of retinoid, looked like it would fit the bill.
In humans, as well as all vertebrate animals, turning a fertilized egg into an embryo with a little beating heart requires that stem cells differentiate, specialize, and generate specific tissues, such as bones, blood vessels and a nervous system. This process is kickstarted and regulated by retinal. Animals can't produce their own retinal, though, they must ingest it from plants, or from animals that eat plants.
"We know plants have the ability to produce this compound, that it's very important for animal development, and so it was very tempting to check its role in plant development as well," said Dickinson, who led this study as part of her postdoctoral research at Duke.
In order for plants to put retinal to good use, retinal molecules must form a tag-team with a protein inside the plant cell, in a process called protein binding.
To test if retinal was indeed behind lateral root development, Dickinson and her team treated seedlings with a dye that glows when retinal is bound by a protein inside a cell. As the seedling grew, glowing dots appeared near the tip of the main root. Soon after, a lateral root would grow from those glowing spots.
The process repeated at regular intervals as the seedling developed, showing that the growth of a lateral root was preceded by a peak in retinal binding.
To confirm their findings, the team applied retinal directly to the plants' primary root. Seedlings that got a retinal booster developed more lateral roots than normal.
To be extra sure, the team applied a compound that made plants incapable of producing retinal, and saw that these seedlings made very few lateral roots.
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