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JXB Advance Access published online on October 9, 2009
Journal of Experimental Botany, doi:10.1093/jxb/erp294
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© 2009 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/2.5/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

Physiological and molecular changes in Oryza meridionalis Ng., a heat-tolerant species of wild rice

Andrew P. Scafaro1, Paul A. Haynes2 and Brian J. Atwell1,*

1Department of Biological Sciences, Macquarie University, NSW 2109, Australia
2Department of Chemistry and Biomolecular Sciences, Macquarie University, NSW 2109, Australia

* To whom correspondence should be addressed: E-mail: batwell{at}rna.bio.mq.edu.au

Oryza meridionalis Ng. is a wild relative of Oryza sativa L. found throughout northern Australia where temperatures regularly exceed 35 °C in the monsoon growing season. Heat tolerance in O. meridionalis was established by comparing leaf elongation and photosynthetic rates at 45 °C with plants maintained at 27 °C. By comparison with O. sativa ssp. japonica cv. Amaroo, O. meridionalis was heat tolerant. Elongation rates of the third leaf of O. meridionalis declined by 47% over 24 h at 45 °C compared with a 91% decrease for O. sativa. Net photosynthesis was significantly higher in O. sativa at 27 °C whereas the two species had the same assimilation rates at 45 °C. The leaf proteome and expression levels of individual heat-responsive genes provided insight into the heat response of O. meridionalis. After 24 h of heat exposure, many enzymes involved in the Calvin Cycle were more abundant, while mRNA of their genes generally decreased. Ferredoxin-NADP(H) oxidoreductase, a key enzyme in photosynthetic electron transport had both reduced abundance and gene expression, suggesting light reactions were highly susceptible to heat stress. Rubisco activase was strongly up-regulated after 24 h of heat, with the large isoform having the largest relative increase in protein abundance and a significant increase in gene expression. The protective proteins Cpn60, Hsp90, and Hsp70 all increased in both protein abundance and gene expression. A thiamine biosynthesis protein (THI1), previously shown to act protectively against stress, increased in abundance during heat, even as thiamine levels fell in O. meridionalis.

Key words: Calvin Cycle, dark reaction, ferredoxin-NADP(H) oxidoreductase, heat shock protein, heat stress, leaf elongation, O. meridionalis, Rubisco activase, thiamine biosynthesis protein (THI1)

Received 7 May 2009; Revised 10 August 2009 Accepted 8 September 2009


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