JXB Advance Access originally published online on March 28, 2008
Journal of Experimental Botany 2008 59(6):1353-1362; doi:10.1093/jxb/ern042
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© 2008 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/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Respiration of thermogenic inflorescences of Philodendron melinonii: natural pattern and responses to experimental temperatures
1Ecology and Evolutionary Biology, University of Adelaide, Adelaide, S.A. 5005, Australia
2Laboratoire d'Evolution et Diversité Biologique UMR 5174, Université Paul Sabatier, 31062 Toulouse Cedex 9, France
* To whom correspondence should be addressed. E-mail: roger.seymour{at}adelaide.edu.au
The patterns of temperature and respiratory changes in the protogynous inflorescences of Philodendron melinonii (Araceae) were studied in the field in French Guiana. These are the first respiratory measurements from a member of the large subgenus Philodendron, a group previously thought to lack thermoregulatory inflorescences, in contrast to thermoregulatory Philodendron species of the subgenus Meconostigma. Heating by the male and sterile male florets was strong on the first evening of anthesis when beetles are attracted and the female florets are receptive. Heat production of the inflorescence peaked at 
0.9 W and spadix temperature reached 39.5 °C, a level somewhat independent of ambient temperature. Thermogenesis continued throughout the night and the next day, but at a lower level, and floral temperatures fell. On the second evening, when pollen was shed, there was a small elevation in respiration and spadix temperature. Responses of cut spadix sections to experimental step changes in ambient temperature resulted in a prompt response in floral temperature and respiration rate in the direction of the change and then a much slower regulatory adjustment in the opposite direction. These responses are consistent with an immediate van 't Hoff effect, followed by up- or down-regulation of thermogenesis. However, the responses required several hours. It is concluded that the male floret tissues possess the same thermoregulatory mechanism of more precise thermoregulatory species, but a combination of small spadix size (that favours heat loss), moderate thermogenic capacity (that limits heating rate), and slow reaction time (that causes long lags between temperature change and the regulatory response) result in poor thermoregulatory performance during the second day.
Key words: Arum lily, heat production, inflorescence, Philodendron, protogynous, regulation, respiration, thermogenesis, van 't Hoff effect
Received 29 December 2007; Revised 23 January 2008 Accepted 24 January 2008
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