Poster: Oxidative Stress

Abs # 122: Salicylic Acid Synthesis in Ozone-exposed Tobacco Leaves

Presenter:	Ogawa, Daisuke , ogawa.daisuke@nies.go.jp
Authors	Ogawa, Daisuke  (A)   Nobuyoshi, Nakajima  (B)   Masanori, Tamaoki  (B)   Mitsuko, Aono  (B)   Akihiro, Kubo  (B)   Hiroshi, Kamada  (A)   Hikaru, Saji  (B)
Affiliations:	(A): Tsukuba university (B): National Institute for Environmental Studies

Ozone, a major photochemical oxidant, induces salicylic acid (SA) synthesis prior to exhibit leaf damage. It is generally thought that SA promotes the leaf injuries during ozone exposure. Two pathways for SA synthesis, one is via phenylalanine as precursor and another is from isochorismate, have shown to be involved in systemic acquired resistance. However, SA biosynthesis induced by ozone has not well defined. When 4 weeks-old tobacco (Nicotiana tabacum cv. SR-1) plants were exposed to 0.2 ppm of ozone, the level of SA became a peak at 6h. At the time, enzyme activity of phenylalanine ammonia-lyase (PAL), its mRNA, and mRNA for chorismate mutase increased remarkably. But the level of transcript for isochorismate synthase was decreased. These results indicate SA may be synthesized from phenylalanine in ozone-exposed tobacco plants. It is well known that ethylene also promote the leaf damage in ozone-exposed plants. To clarify whether SA synthesis in ozone-exposed tobacco is affected by ethylene, we determined level of SA and activity of PAL in transgenic tobacco that exhibits suppressed ozone-induced ethylene production. Ethylene production from ozone-exposed transgenic tobacco was a half those of wild type. Accumulation of SA, PAL activity and its mRNA was suppressed in ozone-exposed transgenic plants. These results indicate that ethylene signaling may affect ozone induced SA level by participating in the regulation of ozone-induced PAL expression.