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Plant and Cell Physiology Advance Access originally published online on February 10, 2009
Plant and Cell Physiology 2009 50(3):644-651; doi:10.1093/pcp/pcp022
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Glucose-Induced Delay of Seed Germination in Rice is Mediated by the Suppression of ABA Catabolism Rather Than an Enhancement of ABA Biosynthesis

Guohui Zhu1, Nenghui Ye2 and Jianhua Zhang2,*

1College of Life Science, South China Agricultural University, Guangdong, PR China
2Department of Biology, Hong Kong Baptist University, Hong Kong, PR China

*Corresponding author: E-mail, jzhang{at}hkbu.edu.hk; Fax, +852-34115995.


  Abstract

Both glucose and ABA play crucial roles in the regulation of seed germination and post-germination development. In Arabidopsis thaliana, up-regulation of ABA biosynthesis is suggested as one of the possible mechanisms mediating the glucose-induced delay in seed germination. Since the endogenous ABA level is controlled by the equilibrium between ABA biosynthesis and catabolism, we investigated how this equilibrium is related to the regulation of seed germination by glucose in rice. When ABA biosynthesis was inhibited by nordihydroguaiaretic acid (NDGA), an inhibitor of the ABA anabolic enzyme 9-cis-epoxycarotenoid dioxygenase (NCED), rice seed germination showed no response. In contrast, inhibition of ABA catabolism by diniconazole significantly arrested seed germination, suggesting that the regulation of ABA catabolism plays a major role. Further experiments indicated that the expression of OsABA8ox3, a key gene in ABA catabolism and encoding ABA 8'-hydroxylase in rice, was significantly increased during the first 6 h of imbibition, which was consistent with the decline of ABA content in the imbibed seeds. Expression of OsABA8ox genes, especially OsABA8ox2 and OsABA8ox3, was sensitively suppressed in the presence of exogenously supplied glucose. In contrast, the expression profiles of OsNCED genes that control the limiting step of ABA biosynthesis showed no significant changes in response to low levels of glucose. Our results demonstrated that the glucose-induced delay of seed germination is a result of the suppression of ABA catabolism rather than any enhancement of ABA biosynthesis during rice seed germination.

Keywords: ABA - ABA biosynthesis - ABA catabolism - Rice (Oryza sativa) - Seed germination - Sugar sensing.

Abbreviations: ABA8ox, ABA 8'-hydroxylase; NCED, 9-cis-epoxycarotenoid dioxygenase; NDGA, nordihydroguaiaretic acid; PA, phaseic acid; qRT-PCR, quantitative real-time PCR.

(Received November 11, 2008; Accepted February 2, 2009)
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