Defense/stress responses elicited in rice seedlings exposed to the gaseous air pollutant sulfur dioxide

This report examines for the first time, the response of rice (Oryza sativa japonica-type cv. Nipponbare) seedlings exposed to the air pollutant sulfur dioxide (SO2). Distinctive reddish-brown necrotic spots and interveinal browning appeared on the leaf surface after exposure to SO2, over control, partly reminiscent of the hypersensitive reaction lesions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting analysis revealed strong induction of ascorbate peroxidase(s), and changes in cysteine proteinase inhibitors ('phytocystatins')-like proteins. Employing classical two-dimensional electrophoresis (2-DE) followed by amino acid sequencing, we identified several changes in the 2-DE protein profiles Of SO2-fumigated leaves. Most prominent changes in leaves were the induced accumulation of a pathogenesis-related (PR) class 5 (OsPR5) protein, three PR 10 class proteins (OsPR10s), a novel ATP-dependent CLP protease, and an unknown protein. Subsequent Northern analysis showed potent accumulation of OsPR5 and OsPR10 transcripts in leaves. Finally, mass spectrometry analysis revealed a strong production of phytoalexins, sakuranetin and momilactone A in SO2 stressed leaves. Our results not only demonstrate the highly damaging effect Of SO2, but also identify SO2 triggered multiple events linked with defense/stress response in the leaves of rice seedlings. (C) 2002 Elsevier Science B.V. All rights reserved.