Dry days trigger leaves to send a surprising growth signal telling roots
to keep growing

Date:
June 26, 2023
Source:
University of Cambridge
Summary:
Scientists have discovered a new molecular signalling pathway,
triggered when leaves are exposed to low humidity, that ensures
plant roots keep growing towards water. A new study has found that
when the leaves of a plant are exposed to dry air (low humidity),
they send a shoot-to-root signal, using abscisic acid (ABA),
to tell the roots to keep growing.

This is a surprising finding as ABA is usually thought to be a
growth inhibitor, not a growth promoter.


Facebook Twitter Pinterest LinkedIN Email

==========================================================================
FULL STORY ========================================================================== Scientists at the Sainsbury Laboratory Cambridge University (SLCU) have discovered a new molecular signalling pathway, triggered when leaves
are exposed to low humidity, that ensures plant roots keep growing
towards water.

In dry soil conditions, plants take action to try and conserve water by producing the drought stress hormone abscisic acid (ABA). For decades
plant scientists thought that in response to dry soil, ABA was made
in the roots and then transported to the leaves. In this root-to-shoot signalling pathway, ABA closes microscopic leaf pores, called stomata,
to prevent water loss from leaves. In recent years, scientists have
shown that other root-to-shoot signals also tell leaves to make their
own ABA to conserve water.

A new study has found that when the leaves of a plant are exposed to dry
air (low humidity), they send a signal in the opposite direction to the
plant's roots -- also using ABA -- to tell them to keep growing. This is
a surprising finding as ABA is usually thought to be a growth inhibitor,
not a growth promoter.

This shoot-to-root signalling pathway potentially helps the plant to
search for water deeper down into the soil, giving it a greater chance
of survival.

With the drought response now well documented in roots and not so much
research done in shoot-to-root signalling, Dr Alexander Jones' research
team wanted to find out more about what was happening above-ground in
the leaves under dry air conditions. The low humidity shoot-to-root
signalling they discovered could be acting as an early warning for the
plant to prepare for future water shortages.

The revelations, published in Nature Plants, were made possible through
the Jones team's design and re-engineering of a next-generation biosensor, ABACUS2.

"We've known for several years that, at low humidity, plants prioritise
root growth. In many species when the humidity decreases, even though photosynthesis and shoot growth is reduced, the root growth is maintained
or even increased," said Dr James Rowe, first author of the study.

"The molecular mechanisms behind this phenomenon have been a mystery until ABACUS2 allowed us to measure ABA concentrations at the cellular level in Arabidopsis thaliana seedlings. We saw that when the leaves experience
low humidity stress that ABA accumulates in the root tips. The leaves
are reacting to the dry air and telling the roots to continue growing,
enabling plants to maintain foraging of deeper soil for water." What is perhaps even more surprising is that ABA is historically thought of as a
growth inhibitor. "Even some plant scientists are surprised to discover
that ABA can promote root growth," Rowe said, "but it's actually really important so that plants can keep searching for water under the ground
during water stress." ABA concentration levels are key -- just the right amount of ABA maintains root growth, but too much ABA and the roots will
stop growing.

Dr Alexander Jones says this sensitivity to ABA concentration means the
plant does not overreact: "The root ABA comes from the phloem, which
transports sugars and hormones from the shoot and is unloaded in the
root tip. ABA signalling can fine-tune root growth as humidity varies,"
Jones said. "Low humidity at the leaves regulates ABA accumulation in the roots, and vice-versa, low soil moisture at the roots regulates ABA in
the leaves. This indicates that the root and shoot can each systemically regulate each other's responses to stresses that may only be experienced locally, thus providing a robust system to overcome water stress."
"This is useful fundamental information to help in understanding the physiological changes happening to crops grown under irrigation where the
air may be dry, but the roots are growing in wet soil -- an increasingly prevalent condition with climate change." Rowe hypothesises that there
could possibly be two signals in play and future research will look at identifying what signalling is happening between the leaves and roots
under drought and low humidity stress.

This research was funded by The Gatsby Charitable Foundation and
Biotechnology and Biological Sciences Research Council (BBSRC).

* RELATED_TOPICS
o Plants_&_Animals
# Endangered_Plants # Drought # Soil_Types # Botany #
Organic # Agriculture_and_Food # Nature # Trees
* RELATED_TERMS
o Root_vegetable o Nicotine o Ginger o Hydroponics o Fertilizer
o Herbal_tea o Plant_cell o Purple_loosestrife

========================================================================== Story Source: Materials provided by University_of_Cambridge. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. James Rowe, Mathieu Grange'-Guermente, Marino Exposito-Rodriguez,
Rinukshi Wimalasekera, Martin O. Lenz, Kartika N. Shetty, Sean
R. Cutler, Alexander M. Jones. Next-generation ABACUS biosensors
reveal cellular ABA dynamics driving root growth at low aerial
humidity. Nature Plants, 2023; DOI: 10.1038/s41477-023-01447-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230626163430.htm

--- up 1 year, 17 weeks, 10 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)