Metabolite profiling reveals tissue- and temperature-specific metabolomic responses in thermoregulatory male florets of Dracunculus vulgaris (Araceae)
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The male part of the spadix of Dracunculus vulgaris exhibits a degree of temperature regulation by inversely controlled heat production over a 20–35 °C range of tissue temperature. To clarify the effects of temperature on cellular metabolism, comparative analysis was performed using 51 metabolites from two distinct tissues (florets and pith) of thermogenic male spadices that had been temperature clamped at either 20 (to produce high respiration) or 35 °C (to produce low respiration). Principal component analysis and hierarchical clustering analysis showed that changes in metabolites in the florets, but not in the pith, were associated with temperature change. The energy charge in the florets treated at 20 °C was significantly higher than that of the florets treated at 35 °C. This indicated the presence of an increased energy-producing pathway that ultimately led to an increased level of thermogenesis at 20 °C. Intriguingly, succinate, a direct substrate for complex II in the mitochondrial respiratory chain, was the metabolite most significantly affected in our analysis, with its concentration in the florets 3.5 times higher at 20 than at 35 °C. However, the mitochondria fed with succinate showed that state 2 and 3 respirations and the capacity of the alternative and cytochrome pathways were all significantly higher at 35 than at 20 °C. Taken together, the results show that the male florets are the primary sites for temperature-induced changes in metabolomic pathways, although succinate-stimulated mitochondrial respiration, per sé, is not the control mechanism for thermoregulation in D. vulgaris.
KeywordsDracunculusvulgaris Thermoregulation Temperature Hierarchical clustering analysis Principal component analysis Energy charge
This study was partly supported by the Japan Society for the Promotion of Science (JSPS) (Grant-in-Aid for Scientific Research (B) (#22405001 and #24380182), by the FY 2010 Researcher Exchange Program between JSPS and Australian Academy of Science, and by the Prime Minister’s Education Assistance Program for Japan. Support from the Australian Research Council Discovery Grant (DP0771854) is appreciated. Y.K. is supported by a Research Fellowship of the JSPS for Young Scientists. We also thank for Mick Brew who raised D. vulgaris in his garden.
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