Journal Article

Salicylic Acid Accumulation Under O<sub>3</sub> Exposure is Regulated by Ethylene in Tobacco Plants

Daisuke Ogawa, Nobuyoshi Nakajima, Tomoharu Sano, Masanori Tamaoki, Mitsuko Aono, Akihiro Kubo, Machi Kanna, Motohide Ioki, Hiroshi Kamada and Hikaru Saji

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 7, pages 1062-1072
Published in print July 2005 | ISSN: 0032-0781
Published online July 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci118
Salicylic Acid Accumulation Under O3 Exposure is Regulated by Ethylene in Tobacco Plants

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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Ozone (O3), a major photochemical oxidant, induces leaf injury concomitant with salicylic acid (SA) synthesis. In pathogen-infected leaves, SA is synthesized via two pathways, involving phenylalanine or isochorismate. SA biosynthesis under O3 fumigation is not well understood. When we applied 14C-labeled benzoic acid (a precursor of SA in the pathway via phenylalanine) to O3-exposed tobacco leaves, it was effectively metabolized to SA. However, the activity and mRNA level of isochorismate synthase (ICS) were not increased. In contrast, ICS activity was increased in O3-exposed Arabidopsis thaliana L. These results suggest that SA is synthesized via benzoic acid from phenylalanine in O3-exposed tobacco leaves but via isochorismate in Arabidopsis. Ethylene is a plant hormone that promotes leaf damage in O3-exposed plants. During O3 exposure, transgenic plants with a phenotype of reduced O3-induced ethylene production accumulated less SA than did wild-type plants. O3 increased the activity of phenylalanine ammonia-lyase (PAL) and the transcript levels of the chorismate mutase (CM) and PAL genes in wild-type tobacco, but their induction was suppressed in the transgenic plants. These results indicate that ethylene promotes SA accumulation by regulating the expression of the CM and PAL genes in O3-exposed tobacco.

Keywords: Arabidopsis; Benzoic acid; Chorismate mutase (CM); Isochorismate synthase (ICS); Leaf injury; Phenylalanine ammonia-lyase (PAL); ACC, 1-aminocyclopropane-1-carboxylate; ACS, 1-aminocyclopropane-1-carboxylate synthase; AOS, active oxygen species; BA, benzoic acid; BA2H, benzoic acid 2-hydroxylase; CM, chorismate mutase; ICS, isochorismate synthase; PAL, phenylalanine ammonia-lyase; RT–PCR, reverse transcription–polymerase chain reaction; SA, salicylic acid; TMV, tobacco mosaic virus

Journal Article.  6843 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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