Poster: Root Biology

Abs # 519: Volatiles of two monoterpenoids, borneol and bornyl acetate, induce different root growth patterns to Arabidopsis seedlings

Presenter:	Horiuchi, Jun-ichiro , junjun@kais.kyoto-u.ac.jp
Authors	Horiuchi, Jun-ichiro  (A) (C)  Nishioka, Takaaki  (A) (C)  Takabayashi, Junji  (B) (C)
Affiliations:	(A): Graduate School of Agriculture, Kyoto University (B): Center for Ecological Research, Kyoto University; Otsuka 509-3, Hirano, Kamitanakami, Otsu, 520-2113, Japan (C): Crest of JST (Japan Science and Technology Corporation)

Higher plants synthesize a great variety of monoterpenoid natural products, which are thought to be involved in plant-plant interactions, such as toxic effects on seed germination, activation of plant genes and interference of roots plasma membrane potentials. Nonterpenoid plant volatiles, trans-2-hexenal and methyl jasmonate that are also involved in plant-plant interactions, inhibit Arabidopsis root growth. Here we report that Arabidopsis seedlings show different root growth patterns in response to monoterpenoid volatiles of borneol and bornyl acetate. Arabidopsis seedlings were grown on the surface of agar plate in a vertical position, and exposed to aerial borneol. We observed growth patterns of the roots. The roots of seedlings exposed to borneol were larger in the diameter of their tips, short in the length, with many root hairs, and expanded root cells. These features were the same as those observed in the root of cobra mutant. Moreover, the root of seedlings showed different sensitivity to optical isomers of borneol: (+)-isomer was about three times more effective than the (-)-isomer. Seedlings exposed to aerial bornyl acetate, in which the hydroxyl group in borneol is replaced to an acetyloxy group, exhibited wavy growth pattern. The rows of epidermal cells were twisted around the root axis without forming large diameter root tip. These responses were the same typically observed when roots of Arabidopsis seedlings suffer from obstacle-touching stimulus. When seedlings exposed to aerial camphore having an oxy group instead of the hydroxyl group in borneol, their root growth was similar to the control. The above results indicate that Arabidopsis roots respond differently to monoterpenoids with different chemical functional groups.