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JXB Advance Access published online on October 4, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm174
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Expression of ASCORBATE PEROXIDASE 8 in roots of rice (Oryza sativa L.) seedlings in response to NaCl

Chwan-Yang Hong1, Yi Ting Hsu2, Yu-Chang Tsai2,* and Ching Huei Kao2 {dagger}

1Department of Agricultural Chemistry and Institute of Biotechnology, National Taiwan University, Taipei, Taiwan, Republic of China
2Department of Agronomy, National Taiwan University, Taipei, Taiwan, Republic of China

{dagger} To whom correspondence should be addressed. E-mail: kaoch{at}ntu.edu.tw

Reactive oxygen species are thought to play an important role in NaCl stress. Therefore, the expression patterns of the gene family encoding the H2O2-scavenging enzyme ascorbate peroxidase (APx; EC1.11.1.11) were analysed in roots of etiolated rice (Oryza sativa L.) seedlings in response to NaCl stress. Applying semi-quantitative RT-PCR, the mRNA levels were quantified for two cytosolic (OsAPx1 and OsAPx2), two peroxisomal (OsAPx3 and OsAPx4), and four chloroplastic (OsAPx5, OsAPx6, OsAPx7, and OsAPx8) isoforms identified in the rice genome. NaCl at 150 mM and 200 mM increased the expression of OsAPx8 and the activities of APx, but had no effect on the expression of OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, OsAPx6, and OsAPx7 in rice roots. However, NaCl at 300 mM up-regulated OsAPx8 expression, increased APx activity, and down-regulated OsAPx7 expression, but had no effect on the expression of OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, and OsAPx6. The accumulation of abscisic acid (ABA) in response to NaCl was observed in rice roots. Exogenously applied ABA also specifically enhanced the expression of OsAPx8 in rice roots. The accumulation of ABA in rice roots in response to NaCl was inhibited by fluridone (Flu), an inhibitor of carotenoid biosynthesis. Flu treatment also suppressed NaCl-enhanced OsAPx8 expression and APx activity. The effect of Flu on the expression of OsAPx8 and increase in APx activity was reversed by the application of ABA. It appears that NaCl-enhanced expression of OsAPx8 in rice roots is mediated through an accumulation of ABA. Evidence is provided to show that Na+ but not Cl– is required for enhancing OsAPx8 expression, APx activity, and ABA accumulation in rice roots treated with NaCl. H2O2 treatment resulted in an enhancement of OsAPx8 induction but no accumulation of ABA. Diphenylene iodonium treatment, which is known to inhibit NaCl-induced accumulation of H2O2 in rice roots, did not suppress OsAPx8 induction and ABA accumulation by NaCl. It appears that H2O2 is not involved in the regulation of NaCl-induced OsAPx8 expression in rice roots.

Key words: Abscisic acid, ascorbate peroxidase, hydrogen peroxide, Oryza sativa, salt stress

* Present address: Department of Biochemistry and Cell Biology, Rice University, MS-140, Houston, TX 77005, USA.

Received 28 March 2007; Revised 26 June 2007 Accepted 29 June 2007


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