Areal (+)-borneol modulates root morphology, auxin signalling and meristematic activity in Arabidopsis roots

One of the characteristic aspects of odour sensing in humans is the
activation of olfactory receptors in a slightly different manner to
different enantiomers. Here, we focused on whether plants showed
enantiomer-specific responses similar to that in humans. We exposed
Arabidopsis seedlings to methanol (control) and (+)- or (−)-borneol, and
found that only (+)-borneol reduced the root length. Furthermore, the
root-tip width was more increased upon (+)-borneol exposure than upon
(−)-borneol exposure. In addition, root-hair formation was observed near
the root tip in response to (+)-borneol. Auxin signalling was strongly
reduced in the root tip following exposure to (+)-borneol, but was
detected following exposure to (−)-borneol and methanol. Similarly, in the
root tip, the activity of Cyclin B1:1 was detected on exposure to
(−)-borneol and methanol, but not on exposure to (+)-borneol, indicating
that (+)-borneol inhibits the meristematic activity in the root. These
results partially explain (+)-borneol-specific reduction in the root
length of Arabidopsis. Our results indicate the presence of a sensing
system specific for (+)-borneol in Arabidopsis.