A better dye job for roots—in plants

In these two images showing different fluorescent markers within the Arabidopsis root tip, the image on the right indicates auxin signaling (green) within the plant’s outer layer (red outlines), which within the image on the left defines the onset of acidification (blue outlines) important for cellular growth/elongation. Credit: Elke Barbez/Gregor Mendel Institute

Once we start coloring our hair, we may be surprised to learn in which we begin to have a problem in common with plant biologists: finding the right dye for our roots. within the case of the biologists, just the right chemical can be needed to measure exactly how plant roots grow. right now, a researcher at the Salk Institute has discovered a fluorescent dye in which, paired with additional imaging techniques, reveals root growth to be influenced by a major plant hormone more than previously thought.


The work, which appears within the Proceedings of the National Academy of Sciences the week of May 29, 2017, could be useful for many types of plant studies, as well as more fully understanding the hormone auxin, which can be instrumental for growth as well as also many additional critical plant processes. Insights into auxin could, for example, inform the production of faster-growing crops or help mitigate such effects of climate change as drought or early flowering.

“Over 130 years ago, Charles Darwin postulated in which there might be a growth-promoting substance in plants,” says Associate Professor Wolfgang Busch, a member of Salk’s Plant Molecular as well as also Cellular Biology Laboratory as well as also senior author of the fresh paper. “Today we know in which This particular substance can be the hormone auxin, as well as also modern scientific tools are finally allowing us to deeply probe its role as a major driver of plant structure as well as also growth.”

One of the longstanding mysteries about plants can be how they grow, because the rigid external cell wall in which gives them structural support also constrains cells by expanding. One working explanation can be called the acid growth hypothesis, which says in which auxin tells plant cells to pump acid into the space between the cells as well as also the surrounding cell wall to trigger cell-wall-loosening enzymes. Just as loosening our belt after a big meal gives our belly room to expand, loosening the cell wall gives plant cells room to grow. The acidification theory has been shown to be fairly accurate for plant shoots, although has been harder to prove for roots. Some studies have found in which auxin actually stimulates alkalinization (the opposite of acidification) in roots. One of the complications of understanding This particular can be in which pH can be very hard to measure in roots.

The Salk-led team, which included researchers by Vienna’s Gregor Mendel Institute of Molecular Plant Biology (where Busch was formerly based), set out to explore the question of how roots grow. They knew they first had to overcome the problem of how to measure pH to determine acidity. So they tested several chemicals they thought might be not bad pH-sensitive dyes as well as also found in which a fluorescent chemical (abbreviated HPTS) fit the bill. The team’s tests confirmed the dye reliably indicated different pH levels in ways in which could be visualized with an instrument called a confocal laser-scanning microscope.

They next set about establishing in which pH can be, in fact, correlated with cell growth. They measured cell length within the roots of the weed Arabidopsis thaliana (a relative of cabbage) before as well as also after immersing plant seedlings in growth medium as well as also checking their pH. Before cells began to grow, pH was alkaline, during growth pH was acidic, as well as also at the end of the growth period pH returned to its pre-growth alkalinity. The team found they were also able to trigger or stop growth by immersing the roots in acidic or alkaline liquids. Together, these experiments confirmed in which acidification promotes the elongation of cells within the root.

“in which’s very fascinating to observe at a cellular level in which a simple chemical characteristic like pH can be such a driving force for root cell elongation,” says Elke Barbez, a postdoctoral fellow at the Gregor Mendel Institute as well as also the paper’s first author.

Next, the team turned to the question of whether the acidification was caused by auxin. To visualize the hormone, they used fluorescent tags in which were attached to a protein in which binds to auxin as well as also then measured cell length, pH as well as also auxin levels in normal seedlings as well as in seedlings in which could not make the hormone or could not correctly respond to in which.

Their results pointed to a more complex role for auxin than previously thought: at low concentrations, auxin did, in fact, trigger acidification as well as also cell-wall loosening, permitting root growth. although at high concentrations, auxin triggered alkalinization, which inhibited growth. The inhibiting effect, however, only lasted For 2 hours. The team’s work offers a clue as to why previous studies have been so confusing or contradictory: at timescales in which are too brief, the dual (“biphasic”) nature of auxin isn’t apparent.

“We are excited by these results not only because they clarify the complex nature of auxin signaling, although also because understanding how This particular major plant hormone works at different timescales could be hugely important to any efforts to enhance crop productivity or enhance root growth as a way to buffer plants by drought,” adds Busch.


Explore further:
Core mechanism for root growth identified

More information:
Elke Barbez el al., “Auxin steers root cell expansion via apoplastic pH regulation in Arabidopsis thaliana,” PNAS (2017). www.pnas.org/cgi/doi/10.1073/pnas.1613499114

Journal reference:
Proceedings of the National Academy of Sciences

Provided by:
Salk Institute

A better dye job for roots—in plants

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