1. ¹Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
2. ²Centre for Research in Plant Science, University of the West of England, Bristol, Coldharbour Lane, Bristol BS16 1QY, UK.

Correspondence: Wei Ming CAI, Tel: +86-21-64042090-3303, E-mail: wmcai@iris.sipp.ac.cn

Received 25 June 2003; Revised 14 April 2004; Accepted 16 April 2004.

Abstract

Responses to oligogalacturonic acid (OGA) were determined in transgenic Arabidopsis thaliana seedlings expressing the calcium reporter protein aequorin. OGA stimulated a rapid, substantial and transient increase in the concentration of cytosolic calcium ([Ca²⁺]_cyt) that peaked after ca. 15 s. This increase was dose-dependent, saturating at ca. 50 g Gal equiv/ml of OGA. OGA also stimulated a rapid generation of H₂O₂. A small, rapid increase in H₂O₂ content was followed by a much larger oxidative burst, with H₂O₂ content peaking after ca. 60 min and declining thereafter. Induction of the oxidative burst by OGA was also dose-dependent, with a maximum response again being achieved at ca. 50 g Gal equiv/mL. Inhibitors of calcium fluxes inhibited both increases in [Ca²⁺]_cyt and [H₂O₂], whereas inhibitors of NADPH oxidase blocked only the oxidative burst. OGA increased strongly the expression of the defence-related genes CHS, GST, PAL and PR-1. This induction was suppressed by inhibitors of calcium flux or NADPH oxidase, indicating that increases in both cytosolic calcium and H₂O₂ are required for OGA-induced gene expression.