Researchers at the RIKEN Center for Sustainable Resource Science (CSRS) in
Japan have discovered a small hormone that helps plants retain water even
when none is available in the soil. The study, published in Nature, shows
how the peptide CLE25 moves from the roots to the leaves when water is
scarce and helps prevent water loss by closing pores in the leaf surface.

The team at RIKEN CSRS wanted to find out if plant hormones respond to
abiotic stress. They looked at CLE peptides that are synthesized in the
roots, and at abscisic acid (ABA), a hormone that accumulates in the leaves
and help close pores in response to drought. Applying many CLE peptides to
plant roots showed that only CLE25 led to increased ABA in the leaves and
pore closure. The team concluded that the link between these two events was
the increase in an enzyme necessary for making ABA. They also observed that
CLE25 levels increased in the roots of plants subjected to dehydration
stress, leading to the same results.

To determine if CLE25 moves through the plant circulatory system, the team
used high sensitive mass spectrometry system, and developed a screening
system that can identify movement of the mobile peptides from root to shoot.
The researchers were able to tag CLE25 molecules and observed their movement
from the roots to the leaves, indicating that it was indeed a mobile hormone
and that it likely interacted with other molecules in leaf to produce ABA.

Before investigating how CLE25 induces ABA synthesis once it arrives at the
leaf, the team created mutant plants that lacked CLE25 or ABA and performed
several control experiments that confirmed their findings. After only three
hours of dehydration, plants without CLE25 already showed 7 times less leaf
ABA and had lost more water than control plants. Finally, the team examined
several mutants and discovered that BAM1/BAM3 receptors in leaf were the
link between CLE25 and ABA production.

[www.riken.jp]