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

Department of Biological Sciences, Macquarie University, NSW 2109, Australia.
Journal of Experimental Botany (Impact Factor: 5.53). 10/2009; 61(1):191-202. DOI: 10.1093/jxb/erp294
Source: PubMed


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.

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