Poster: Oxidative Stress

Abs # 121: Differential O₃ sensitivity among Arabidopsis accessions and its relevance to ethylene synthesis

Presenter:	Masanori, Tamaoki , mtamaoki@nies.go.jp
Authors	Masanori, Tamaoki  (A)   Takashi, Matsuyama  (A) (B)  Machi, Kanna  (A)   Nobuyoshi, Nakajima  (A)   Akihiro, Kubo  (A)   Mitsuko, Aono  (A)   Hikaru, Saji  (A)
Affiliations:	(A): National Institute for Environmental Studies (B): TOYOTA Central R&D Labs.

We compared the physiological and molecular responses of two Arabidopsis accessions, Col-0 and Ws, to ozone (O₃) exposure. Observation of visible injury as well as ion-leakage analysis demonstrated clear differences between Col (O₃-tolerant) and Ws (O₃-sensitive). RNA-blot analysis showed that O₃-induced increases in mRNA levels of several ethylene- or salicylic acid inducible genes were substantially higher in Ws than in Col. The time course of induction in various mRNA levels shows that the expression of ethylene-inducible genes was rapidly and more strongly induced by O₃ in Ws than in Col, suggesting that Ws exhibits higher ethylene-signaling. Both the level of mRNA for an O₃-inducible ACC synthase and the level of ethylene generation at 3 h of O₃-exposure were higher in Ws than in Col. The O₃-induced leaf damage was attenuated by the pretreatment with ethylene biosynthesis- and signaling-inhibitors, indicating that the ethylene signaling is required for the O₃-induced leaf injury in Ws. On the other hand, the ethylene-overproducing mutant of Col, eto1-1, displayed significantly increased O₃-induced leaf injury compared to wild type plant. These results indicate that the difference in O₃ sensitivity is dependent on the difference in ethylene production rate between these two accessions. We finally investigated the relationship between the degree of leaf damage and the level of ethylene evolution in twenty different Arabidopsis accessions. Based on the result, the accessions were classified into four types. However, most of them showed significant correlation between the ethylene production level and the degree of leaf injury, suggesting that ethylene-signaling is an important factor for the natural variety of O₃ sensitivity among Arabidopsis accessions.