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JXB Advance Access originally published online on April 4, 2006
Journal of Experimental Botany 2006 57(9):1899-1908; doi:10.1093/jxb/erj131
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© The Author [2006]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Oxalate accumulation and regulation is independent of glycolate oxidase in rice leaves

Hua-Wei Xu1 *, Xiu-Mei Ji1,2 *, Zheng-Hui He3, Wei-Ping Shi1, Guo-Hui Zhu1, Jian-Kang Niu1, Bao-Sheng Li1 and Xin-Xiang Peng1,{dagger}

1Laboratory of Molecular Plant Physiology, College of Life Sciences, South China Agricultural University, Guangzhou 510642, PR China
2Department of Biotechnology, Zhengzhou University, Zhengzhou 450052, PR China
3Department of Biology, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132, USA

{dagger}To whom correspondence should be addressed. E-mail: xpeng{at}scau.edu.cn

Cellular oxalate, widely distributed in many plants, is implicated to play important roles in various functions and is also known to affect food qualities adversely in fruits and vegetables. How oxalate is regulated in plants is currently not well understood. Glycolate oxidase (GLO) has long been considered as an important player in oxalate accumulation in plants. To gain further insight into the biochemical and molecular mechanisms, the possible roles of GLO in the process were studied. Drastically different levels of oxalate could be achieved by treating rice with various nitrogen forms (nitrate versus ammonium). While nitrate stimulated oxalate accumulation, ammonium reduced its level. Such treatments resulted in similar pattern changes for some other related organic acids, such as glycolate, oxaloacetate, and malate. By feeding plants with exogenous glycolate it was possible almost completely to restore the ammonium-decreased oxalate level. Under the two treatments few differences were observed for GLO mRNA levels, protein levels, and in vitro activities. Both Km for glycolate/glyoxylate and Ki for oxalate remained almost the same for GLO purified from either nitrate- or ammonium-fed leaves. A further in vivo study, with transgenic plants carrying an estradiol-inducible GLO antisense gene, showed that, while the estradiol-induced antisense expression remarkably reduced both GLO protein levels and activities, oxalate levels were not significantly altered in the estradiol-treated transgenic plants. Taken together, it is suggested that oxalate accumulation and regulation is independent of GLO in rice leaves.

Key words: Glycolate oxidase, oxalate accumulation, rice


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